diff --git a/examples/pdf-bookmarks.cc b/examples/pdf-bookmarks.cc
index 87a3b9d..00558a3 100644
--- a/examples/pdf-bookmarks.cc
+++ b/examples/pdf-bookmarks.cc
@@ -104,7 +104,7 @@ show_bookmark_details(QPDFOutlineObjectHelper outline, std::vector<int> numbers)
         QPDFObjectHandle dest_page = outline.getDestPage();
         if (!dest_page.isNull()) {
             QTC::TC("examples", "pdf-bookmarks dest");
-            if (page_map.count(dest_page)) {
+            if (page_map.contains(dest_page)) {
                 target = std::to_string(page_map[dest_page]);
             }
         }
diff --git a/examples/pdf-custom-filter.cc b/examples/pdf-custom-filter.cc
index 1a8f14e..ac949a1 100644
--- a/examples/pdf-custom-filter.cc
+++ b/examples/pdf-custom-filter.cc
@@ -276,7 +276,7 @@ StreamReplacer::registerStream(
     // We don't need to process a stream more than once. In this example, we are just iterating
     // through objects, but if we were doing something like iterating through images on pages, we
     // might realistically encounter the same stream more than once.
-    if (this->copied_streams.count(og) > 0) {
+    if (this->copied_streams.contains(og)) {
         return;
     }
     // Store something in copied_streams so that we don't double-process even in the negative case.
diff --git a/examples/pdf-invert-images.cc b/examples/pdf-invert-images.cc
index 09e115d..de2da9b 100644
--- a/examples/pdf-invert-images.cc
+++ b/examples/pdf-invert-images.cc
@@ -52,7 +52,7 @@ ImageInverter::registerImage(
     // Store information about the images based on the object and generation number. Recall that a
     // single image object may be used more than once, so no need to update the same stream multiple
     // times.
-    if (this->copied_images.count(og) > 0) {
+    if (copied_images.contains(og)) {
         return;
     }
     this->copied_images[og] = image.copyStream();
diff --git a/include/qpdf/QPDFObjGen.hh b/include/qpdf/QPDFObjGen.hh
index 8bdeea7..f984668 100644
--- a/include/qpdf/QPDFObjGen.hh
+++ b/include/qpdf/QPDFObjGen.hh
@@ -110,7 +110,7 @@ class QPDFObjGen
         add(QPDFObjGen og)
         {
             if (og.isIndirect()) {
-                if (count(og) > 0) {
+                if (count(og)) {
                     return false;
                 }
                 emplace(og);
diff --git a/libqpdf/JSON.cc b/libqpdf/JSON.cc
index aef1bb4..852e53c 100644
--- a/libqpdf/JSON.cc
+++ b/libqpdf/JSON.cc
@@ -516,11 +516,11 @@ JSON::checkSchemaInternal(
                 }
             }
         }
-        for (auto const& [key, val]: this_dict->members) {
-            if (!sch_dict->members.contains(key)) {
+        for (auto const& item: this_dict->members) {
+            if (!sch_dict->members.contains(item.first)) {
                 QTC::TC("libtests", "JSON key extra in object");
                 errors.emplace_back(
-                    err_prefix + ": key \"" + key +
+                    err_prefix + ": key \"" + item.first +
                     "\" is not present in schema but appears in object");
             }
         }
diff --git a/libqpdf/QPDF.cc b/libqpdf/QPDF.cc
index c048f75..a0c2054 100644
--- a/libqpdf/QPDF.cc
+++ b/libqpdf/QPDF.cc
@@ -564,7 +564,7 @@ QPDF::copyForeignObject(QPDFObjectHandle foreign)
     obj_copier.to_copy.clear();
 
     auto og = foreign.getObjGen();
-    if (!obj_copier.object_map.count(og)) {
+    if (!obj_copier.object_map.contains(og)) {
         warn(damagedPDF(
             other.getFilename() + " object " + og.unparse(' '),
             foreign.getParsedOffset(),
@@ -594,7 +594,7 @@ QPDF::reserveObjects(QPDFObjectHandle foreign, ObjCopier& obj_copier, bool top)
             QTC::TC("qpdf", "QPDF loop reserving objects");
             return;
         }
-        if (obj_copier.object_map.count(foreign_og) > 0) {
+        if (obj_copier.object_map.contains(foreign_og)) {
             QTC::TC("qpdf", "QPDF already reserved object");
             if (!(top && foreign.isPageObject() && obj_copier.object_map[foreign_og].isNull())) {
                 obj_copier.visiting.erase(foreign);
diff --git a/libqpdf/QPDFAcroFormDocumentHelper.cc b/libqpdf/QPDFAcroFormDocumentHelper.cc
index 8f47616..46e87c9 100644
--- a/libqpdf/QPDFAcroFormDocumentHelper.cc
+++ b/libqpdf/QPDFAcroFormDocumentHelper.cc
@@ -85,7 +85,7 @@ QPDFAcroFormDocumentHelper::addAndRenameFormFields(std::vector<QPDFObjectHandle>
                 // this field's /T is always at the end of the fully qualified name, appending to /T
                 // has the effect of appending the same thing to the fully qualified name.
                 std::string old_name = QPDFFormFieldObjectHelper(obj).getFullyQualifiedName();
-                if (renames.count(old_name) == 0) {
+                if (!renames.contains(old_name)) {
                     std::string new_name = old_name;
                     int suffix = 0;
                     std::string append;
@@ -145,7 +145,7 @@ QPDFAcroFormDocumentHelper::removeFormFields(std::set<QPDFObjGen> const& to_remo
     int i = 0;
     while (i < fields.getArrayNItems()) {
         auto field = fields.getArrayItem(i);
-        if (to_remove.count(field.getObjGen())) {
+        if (to_remove.contains(field.getObjGen())) {
             fields.eraseItem(i);
         } else {
             ++i;
@@ -191,7 +191,7 @@ QPDFAcroFormDocumentHelper::getAnnotationsForField(QPDFFormFieldObjectHelper h)
     analyze();
     std::vector<QPDFAnnotationObjectHelper> result;
     QPDFObjGen og(h.getObjectHandle().getObjGen());
-    if (m->field_to_annotations.count(og)) {
+    if (m->field_to_annotations.contains(og)) {
         result = m->field_to_annotations[og];
     }
     return result;
@@ -228,7 +228,7 @@ QPDFAcroFormDocumentHelper::getFieldForAnnotation(QPDFAnnotationObjectHelper h)
     }
     analyze();
     QPDFObjGen og(oh.getObjGen());
-    if (m->annotation_to_field.count(og)) {
+    if (m->annotation_to_field.contains(og)) {
         result = m->annotation_to_field[og];
     }
     return result;
@@ -271,7 +271,7 @@ QPDFAcroFormDocumentHelper::analyze()
         for (auto const& iter: getWidgetAnnotationsForPage(ph)) {
             QPDFObjectHandle annot(iter.getObjectHandle());
             QPDFObjGen og(annot.getObjGen());
-            if (m->annotation_to_field.count(og) == 0) {
+            if (!m->annotation_to_field.contains(og)) {
                 QTC::TC("qpdf", "QPDFAcroFormDocumentHelper orphaned widget");
                 // This is not supposed to happen, but it's easy enough for us to handle this case.
                 // Treat the annotation as its own field. This could allow qpdf to sensibly handle a
@@ -542,7 +542,7 @@ ResourceReplacer::handleToken(QPDFTokenizer::Token const& token)
     bool wrote = false;
     if (token.getType() == QPDFTokenizer::tt_name) {
         std::string name = QPDFObjectHandle::newName(token.getValue()).getName();
-        if (to_replace.count(name) && to_replace[name].count(offset)) {
+        if (to_replace.contains(name) && to_replace[name].contains(offset)) {
             QTC::TC("qpdf", "QPDFAcroFormDocumentHelper replaced DA token");
             write(to_replace[name][offset]);
             wrote = true;
@@ -807,7 +807,7 @@ QPDFAcroFormDocumentHelper::transformAnnotations(
     std::map<QPDFObjGen, QPDFObjectHandle> orig_to_copy;
     auto maybe_copy_object = [&](QPDFObjectHandle& to_copy) {
         auto og = to_copy.getObjGen();
-        if (orig_to_copy.count(og)) {
+        if (orig_to_copy.contains(og)) {
             to_copy = orig_to_copy[og];
             return false;
         } else {
@@ -893,7 +893,7 @@ QPDFAcroFormDocumentHelper::transformAnnotations(
                     auto parent = obj.getKey("/Parent");
                     if (parent.isIndirect()) {
                         auto parent_og = parent.getObjGen();
-                        if (orig_to_copy.count(parent_og)) {
+                        if (orig_to_copy.contains(parent_og)) {
                             obj.replaceKey("/Parent", orig_to_copy[parent_og]);
                         } else {
                             parent.warnIfPossible(
diff --git a/libqpdf/QPDFArgParser.cc b/libqpdf/QPDFArgParser.cc
index c16c18b..08e727c 100644
--- a/libqpdf/QPDFArgParser.cc
+++ b/libqpdf/QPDFArgParser.cc
@@ -71,7 +71,7 @@ QPDFArgParser::selectOptionTable(std::string const& name)
 void
 QPDFArgParser::registerOptionTable(std::string const& name, bare_arg_handler_t end_handler)
 {
-    if (0 != m->option_tables.count(name)) {
+    if (m->option_tables.contains(name)) {
         QTC::TC("libtests", "QPDFArgParser register registered table");
         throw std::logic_error(
             "QPDFArgParser: registering already registered option table " + name);
@@ -84,7 +84,7 @@ QPDFArgParser::registerOptionTable(std::string const& name, bare_arg_handler_t e
 QPDFArgParser::OptionEntry&
 QPDFArgParser::registerArg(std::string const& arg)
 {
-    if (0 != m->option_table->count(arg)) {
+    if (m->option_table->contains(arg)) {
         QTC::TC("libtests", "QPDFArgParser duplicate handler");
         throw std::logic_error(
             "QPDFArgParser: adding a duplicate handler for option " + arg + " in " +
@@ -481,7 +481,7 @@ QPDFArgParser::parseArgs()
             }
 
             if ((!m->bash_completion) && (m->argc == 2) && (m->cur_arg == 1) &&
-                m->help_option_table.count(arg_s)) {
+                m->help_option_table.contains(arg_s)) {
                 // Handle help option, which is only valid as the sole option.
                 QTC::TC("libtests", "QPDFArgParser help option");
                 oep = m->help_option_table.find(arg_s);
@@ -508,8 +508,8 @@ QPDFArgParser::parseArgs()
         }
 
         OptionEntry& oe = oep->second;
-        if ((oe.parameter_needed && (!have_parameter)) ||
-            ((!oe.choices.empty() && have_parameter && (0 == oe.choices.count(parameter))))) {
+        if ((oe.parameter_needed && !have_parameter) ||
+            (!oe.choices.empty() && have_parameter && !oe.choices.contains(parameter))) {
             std::string message = "--" + arg_s + " must be given as --" + arg_s + "=";
             if (oe.invalid_choice_handler) {
                 oe.invalid_choice_handler(parameter);
@@ -584,7 +584,7 @@ void
 QPDFArgParser::addChoicesToCompletions(
     option_table_t& option_table, std::string const& option, std::string const& extra_prefix)
 {
-    if (option_table.count(option) != 0) {
+    if (option_table.contains(option)) {
         OptionEntry& oe = option_table[option];
         for (auto const& choice: oe.choices) {
             QTC::TC("libtests", "QPDFArgParser complete choices");
@@ -690,7 +690,7 @@ QPDFArgParser::addHelpTopic(
         QTC::TC("libtests", "QPDFArgParser bad topic for help");
         throw std::logic_error("QPDFArgParser: help topics must not start with -");
     }
-    if (m->help_topics.count(topic)) {
+    if (m->help_topics.contains(topic)) {
         QTC::TC("libtests", "QPDFArgParser add existing topic");
         throw std::logic_error("QPDFArgParser: topic " + topic + " has already been added");
     }
@@ -710,7 +710,7 @@ QPDFArgParser::addOptionHelp(
         QTC::TC("libtests", "QPDFArgParser bad option for help");
         throw std::logic_error("QPDFArgParser: options for help must start with --");
     }
-    if (m->option_help.count(option_name)) {
+    if (m->option_help.contains(option_name)) {
         QTC::TC("libtests", "QPDFArgParser duplicate option help");
         throw std::logic_error("QPDFArgParser: option " + option_name + " already has help");
     }
@@ -782,9 +782,9 @@ QPDFArgParser::getHelp(std::string const& arg)
     } else {
         if (arg == "all") {
             getAllHelp(msg);
-        } else if (m->option_help.count(arg)) {
+        } else if (m->option_help.contains(arg)) {
             getTopicHelp(arg, m->option_help[arg], msg);
-        } else if (m->help_topics.count(arg)) {
+        } else if (m->help_topics.contains(arg)) {
             getTopicHelp(arg, m->help_topics[arg], msg);
         } else {
             // should not be possible
diff --git a/libqpdf/QPDFCryptoProvider.cc b/libqpdf/QPDFCryptoProvider.cc
index 89b5284..df5eff0 100644
--- a/libqpdf/QPDFCryptoProvider.cc
+++ b/libqpdf/QPDFCryptoProvider.cc
@@ -88,7 +88,7 @@ QPDFCryptoProvider::registerImpl_internal(std::string const& name, provider_fn f
 void
 QPDFCryptoProvider::setDefaultProvider_internal(std::string const& name)
 {
-    if (!m->providers.count(name)) {
+    if (!m->providers.contains(name)) {
         throw std::logic_error(
             "QPDFCryptoProvider: request to set default provider to unknown implementation \"" +
             name + "\"");
diff --git a/libqpdf/QPDFJob.cc b/libqpdf/QPDFJob.cc
index 99ccd15..1a74ea4 100644
--- a/libqpdf/QPDFJob.cc
+++ b/libqpdf/QPDFJob.cc
@@ -673,7 +673,7 @@ QPDFJob::checkConfiguration()
             usage("json key \"qpdf\" is only valid for json version > 1");
         }
     } else {
-        if (m->json_keys.contains("objectinfo") || m->json_keys.count("objects")) {
+        if (m->json_keys.contains("objectinfo") || m->json_keys.contains("objects")) {
             usage("json keys \"objects\" and \"objectinfo\" are only valid for json version 1");
         }
     }
@@ -1007,13 +1007,13 @@ QPDFJob::doJSONObjects(Pipeline* p, bool& first, QPDF& pdf)
         for (auto& obj: pdf.getAllObjects()) {
             std::string key = obj.unparse();
 
-            if (all_objects || wanted_og.count(obj.getObjGen())) {
+            if (all_objects || wanted_og.contains(obj.getObjGen())) {
                 JSON::writeDictionaryKey(p, first_object, obj.unparse(), 2);
                 obj.writeJSON(1, p, true, 2);
                 first_object = false;
             }
         }
-        if (all_objects || m->json_objects.count("trailer")) {
+        if (all_objects || m->json_objects.contains("trailer")) {
             JSON::writeDictionaryKey(p, first_object, "trailer", 2);
             pdf.getTrailer().writeJSON(1, p, true, 2);
             first_object = false;
@@ -1021,7 +1021,7 @@ QPDFJob::doJSONObjects(Pipeline* p, bool& first, QPDF& pdf)
         JSON::writeDictionaryClose(p, first_object, 1);
     } else {
         std::set<std::string> json_objects;
-        if (m->json_objects.count("trailer")) {
+        if (m->json_objects.contains("trailer")) {
             json_objects.insert("trailer");
         }
         for (auto og: getWantedJSONObjects()) {
@@ -1048,7 +1048,7 @@ QPDFJob::doJSONObjectinfo(Pipeline* p, bool& first, QPDF& pdf)
     bool all_objects = m->json_objects.empty();
     auto wanted_og = getWantedJSONObjects();
     for (auto& obj: pdf.getAllObjects()) {
-        if (all_objects || wanted_og.count(obj.getObjGen())) {
+        if (all_objects || wanted_og.contains(obj.getObjGen())) {
             auto j_details = JSON::makeDictionary();
             auto j_stream = j_details.addDictionaryMember("stream", JSON::makeDictionary());
             bool is_stream = obj.isStream();
@@ -1170,7 +1170,7 @@ QPDFJob::addOutlinesToJson(
         JSON j_destpage = JSON::makeNull();
         if (page.isIndirect()) {
             QPDFObjGen og = page.getObjGen();
-            if (page_numbers.count(og)) {
+            if (page_numbers.contains(og)) {
                 j_destpage = JSON::makeInt(page_numbers[og]);
             }
         }
@@ -1913,7 +1913,7 @@ get_afdh_for_qpdf(
     std::map<unsigned long long, std::shared_ptr<QPDFAcroFormDocumentHelper>>& afdh_map, QPDF* q)
 {
     auto uid = q->getUniqueId();
-    if (!afdh_map.count(uid)) {
+    if (!afdh_map.contains(uid)) {
         afdh_map[uid] = std::make_shared<QPDFAcroFormDocumentHelper>(*q);
     }
     return afdh_map[uid].get();
@@ -1931,7 +1931,7 @@ QPDFJob::doUnderOverlayForPage(
     QPDFPageObjectHelper& dest_page)
 {
     int pageno = 1 + QIntC::to_int(page_idx);
-    if (!(pagenos.count(pageno) && pagenos[pageno].count(uo_idx))) {
+    if (!(pagenos.contains(pageno) && pagenos[pageno].contains(uo_idx))) {
         return "";
     }
 
@@ -1950,7 +1950,7 @@ QPDFJob::doUnderOverlayForPage(
             v << "    " << uo.filename << " " << uo.which << " " << from_pageno << "\n";
         });
         auto from_page = pages.at(QIntC::to_size(from_pageno - 1));
-        if (fo[from_pageno].count(uo_idx) == 0) {
+        if (!fo[from_pageno].contains(uo_idx)) {
             fo[from_pageno][uo_idx] = pdf.copyForeignObject(from_page.getFormXObjectForPage());
         }
 
@@ -2462,7 +2462,7 @@ QPDFJob::handlePageSpecs(QPDF& pdf, std::vector<std::unique_ptr<QPDF>>& page_hea
     std::vector<QPDFPageData> parsed_specs;
     std::map<unsigned long long, std::set<QPDFObjGen>> copied_pages;
     for (auto& page_spec: m->page_specs) {
-        if (page_spec_qpdfs.count(page_spec.filename) == 0) {
+        if (!page_spec_qpdfs.contains(page_spec.filename)) {
             // Open the PDF file and store the QPDF object. Throw a std::shared_ptr to the qpdf into
             // a heap so that it survives through copying to the output but gets cleaned up
             // automatically at the end. Do not canonicalize the file name. Using two different
@@ -2512,13 +2512,13 @@ QPDFJob::handlePageSpecs(QPDF& pdf, std::vector<std::unique_ptr<QPDF>>& page_hea
         for (auto const& iter: page_spec_qpdfs) {
             std::string const& filename = iter.first;
             ClosedFileInputSource* cis = nullptr;
-            if (page_spec_cfis.count(filename)) {
+            if (page_spec_cfis.contains(filename)) {
                 cis = page_spec_cfis[filename];
                 cis->stayOpen(true);
             }
             QPDF& other(*(iter.second));
             auto other_uuid = other.getUniqueId();
-            if (remove_unreferenced.count(other_uuid) == 0) {
+            if (!remove_unreferenced.contains(other_uuid)) {
                 remove_unreferenced[other_uuid] = shouldRemoveUnreferencedResources(other);
             }
             if (cis) {
@@ -2585,7 +2585,7 @@ QPDFJob::handlePageSpecs(QPDF& pdf, std::vector<std::unique_ptr<QPDF>>& page_hea
     std::set<QPDFObjGen> referenced_fields;
     for (auto& page_data: parsed_specs) {
         ClosedFileInputSource* cis = nullptr;
-        if (page_spec_cfis.count(page_data.filename)) {
+        if (page_spec_cfis.contains(page_data.filename)) {
             cis = page_spec_cfis[page_data.filename];
             cis->stayOpen(true);
         }
@@ -2604,7 +2604,7 @@ QPDFJob::handlePageSpecs(QPDF& pdf, std::vector<std::unique_ptr<QPDF>>& page_hea
             QPDFPageObjectHelper to_copy = page_data.orig_pages.at(QIntC::to_size(pageno));
             QPDFObjGen to_copy_og = to_copy.getObjectHandle().getObjGen();
             unsigned long long from_uuid = page_data.qpdf->getUniqueId();
-            if (copied_pages[from_uuid].count(to_copy_og)) {
+            if (copied_pages[from_uuid].contains(to_copy_og)) {
                 QTC::TC(
                     "qpdf",
                     "QPDFJob copy same page more than once",
@@ -2622,7 +2622,7 @@ QPDFJob::handlePageSpecs(QPDF& pdf, std::vector<std::unique_ptr<QPDF>>& page_hea
             if (this_file) {
                 // This is a page from the original file. Keep track of the fact that we are using
                 // it.
-                first_copy_from_orig = (selected_from_orig.count(pageno) == 0);
+                first_copy_from_orig = (!selected_from_orig.contains(pageno));
                 selected_from_orig.insert(pageno);
             }
             auto new_page = added_page(pdf, to_copy);
@@ -2667,7 +2667,7 @@ QPDFJob::handlePageSpecs(QPDF& pdf, std::vector<std::unique_ptr<QPDF>>& page_hea
     // sure we keep form fields from pages we preserved.
     for (size_t pageno = 0; pageno < orig_pages.size(); ++pageno) {
         auto page = orig_pages.at(pageno);
-        if (selected_from_orig.count(QIntC::to_int(pageno))) {
+        if (selected_from_orig.contains(QIntC::to_int(pageno))) {
             for (auto field: this_afdh->getFormFieldsForPage(page)) {
                 QTC::TC("qpdf", "QPDFJob pages keeping field from original");
                 referenced_fields.insert(field.getObjectHandle().getObjGen());
@@ -2686,7 +2686,7 @@ QPDFJob::handlePageSpecs(QPDF& pdf, std::vector<std::unique_ptr<QPDF>>& page_hea
                 new_fields = pdf.makeIndirectObject(new_fields);
             }
             for (auto const& field: fields.aitems()) {
-                if (referenced_fields.count(field.getObjGen())) {
+                if (referenced_fields.contains(field.getObjGen())) {
                     new_fields.appendItem(field);
                 }
             }
diff --git a/libqpdf/QPDFObjectHandle.cc b/libqpdf/QPDFObjectHandle.cc
index 9ce200e..fba9cbc 100644
--- a/libqpdf/QPDFObjectHandle.cc
+++ b/libqpdf/QPDFObjectHandle.cc
@@ -1184,7 +1184,7 @@ QPDFObjectHandle::mergeResources(
                             initialized_maps = true;
                         }
                         auto rval_og = rval.getObjGen();
-                        if (rval.isIndirect() && og_to_name.count(rval_og)) {
+                        if (rval.isIndirect() && og_to_name.contains(rval_og)) {
                             QTC::TC("qpdf", "QPDFObjectHandle merge reuse");
                             auto new_key = og_to_name[rval_og];
                             if (new_key != key) {
@@ -1208,7 +1208,7 @@ QPDFObjectHandle::mergeResources(
                 }
                 for (auto other_item: other_val.aitems()) {
                     if (other_item.isScalar()) {
-                        if (scalars.count(other_item.unparse()) == 0) {
+                        if (!scalars.contains(other_item.unparse())) {
                             QTC::TC("qpdf", "QPDFObjectHandle merge array");
                             this_val.appendItem(other_item);
                         } else {
@@ -1247,7 +1247,7 @@ QPDFObjectHandle::getUniqueResourceName(
     int max_suffix = min_suffix + QIntC::to_int(names.size());
     while (min_suffix <= max_suffix) {
         std::string candidate = prefix + std::to_string(min_suffix);
-        if (names.count(candidate) == 0) {
+        if (!names.contains(candidate)) {
             return candidate;
         }
         // Increment after return; min_suffix should be the value
diff --git a/libqpdf/QPDFOutlineDocumentHelper.cc b/libqpdf/QPDFOutlineDocumentHelper.cc
index 9028cd3..13107c3 100644
--- a/libqpdf/QPDFOutlineDocumentHelper.cc
+++ b/libqpdf/QPDFOutlineDocumentHelper.cc
@@ -56,7 +56,7 @@ QPDFOutlineDocumentHelper::getOutlinesForPage(QPDFObjGen og)
         initializeByPage();
     }
     std::vector<QPDFOutlineObjectHelper> result;
-    if (m->by_page.count(og)) {
+    if (m->by_page.contains(og)) {
         result = m->by_page[og];
     }
     return result;
diff --git a/libqpdf/QPDFPageObjectHelper.cc b/libqpdf/QPDFPageObjectHelper.cc
index ea866f1..67badaa 100644
--- a/libqpdf/QPDFPageObjectHelper.cc
+++ b/libqpdf/QPDFPageObjectHelper.cc
@@ -593,7 +593,7 @@ QPDFPageObjectHelper::removeUnreferencedResourcesHelper(
     for (auto const& i1: to_filter) {
         for (auto const& n_iter: names_by_rtype[i1]) {
             std::string const& name = n_iter.first;
-            if (!known_names.count(name)) {
+            if (!known_names.contains(name)) {
                 unresolved.insert(name);
                 local_unresolved.insert(name);
             }
@@ -624,10 +624,10 @@ QPDFPageObjectHelper::removeUnreferencedResourcesHelper(
 
     for (auto& dict: rdicts) {
         for (auto const& key: dict.getKeys()) {
-            if (is_page && unresolved.count(key)) {
+            if (is_page && unresolved.contains(key)) {
                 // This name is referenced by some nested form xobject, so don't remove it.
                 QTC::TC("qpdf", "QPDFPageObjectHelper resolving unresolved");
-            } else if (!rf.getNames().count(key)) {
+            } else if (!rf.getNames().contains(key)) {
                 dict.removeKey(key);
             }
         }
diff --git a/libqpdf/QPDFParser.cc b/libqpdf/QPDFParser.cc
index 1690f39..faeba7e 100644
--- a/libqpdf/QPDFParser.cc
+++ b/libqpdf/QPDFParser.cc
@@ -354,9 +354,9 @@ QPDFParser::parseRemainder(bool content_stream)
                     fixMissingKeys();
                 }
 
-                if (!frame->contents_string.empty() && dict.count("/Type") &&
-                    dict["/Type"].isNameAndEquals("/Sig") && dict.count("/ByteRange") &&
-                    dict.count("/Contents") && dict["/Contents"].isString()) {
+                if (!frame->contents_string.empty() && dict.contains("/Type") &&
+                    dict["/Type"].isNameAndEquals("/Sig") && dict.contains("/ByteRange") &&
+                    dict.contains("/Contents") && dict["/Contents"].isString()) {
                     dict["/Contents"] = QPDFObjectHandle::newString(frame->contents_string);
                     dict["/Contents"].setParsedOffset(frame->contents_offset);
                 }
@@ -560,7 +560,7 @@ QPDFParser::fixMissingKeys()
     for (auto const& item: frame->olist) {
         while (true) {
             const std::string key = "/QPDFFake" + std::to_string(next_fake_key++);
-            const bool found_fake = frame->dict.count(key) == 0 && names.count(key) == 0;
+            const bool found_fake = !frame->dict.contains(key) && !names.contains(key);
             QTC::TC("qpdf", "QPDFParser found fake", (found_fake ? 0 : 1));
             if (found_fake) {
                 warn(
diff --git a/libqpdf/QPDFWriter.cc b/libqpdf/QPDFWriter.cc
index d18bb32..de7227d 100644
--- a/libqpdf/QPDFWriter.cc
+++ b/libqpdf/QPDFWriter.cc
@@ -1065,7 +1065,7 @@ void
 QPDFWriter::assignCompressedObjectNumbers(QPDFObjGen og)
 {
     int objid = og.getObj();
-    if ((og.getGen() != 0) || (m->object_stream_to_objects.count(objid) == 0)) {
+    if ((og.getGen() != 0) || (!m->object_stream_to_objects.contains(objid))) {
         // This is not an object stream.
         return;
     }
@@ -1115,7 +1115,7 @@ QPDFWriter::enqueueObject(QPDFObjectHandle object)
                 m->object_queue.push_back(object);
                 obj.renumber = m->next_objid++;
 
-                if ((og.getGen() == 0) && m->object_stream_to_objects.count(og.getObj())) {
+                if ((og.getGen() == 0) && m->object_stream_to_objects.contains(og.getObj())) {
                     // For linearized files, uncompressed objects go at end, and we take care of
                     // assigning numbers to them elsewhere.
                     if (!m->linearized) {
@@ -1285,7 +1285,7 @@ QPDFWriter::willFilterStream(
         filter = true;
         compress_stream = false;
         uncompress = true;
-    } else if (filter_on_write && m->normalize_content && m->normalized_streams.count(old_og)) {
+    } else if (filter_on_write && m->normalize_content && m->normalized_streams.contains(old_og)) {
         normalize = true;
         filter = true;
     } else if (filter_on_write && filter && m->compress_streams) {
@@ -1415,7 +1415,7 @@ QPDFWriter::unparseObject(
 
         if (extensions) {
             std::set<std::string> keys = extensions.getKeys();
-            if (keys.count("/ADBE") > 0) {
+            if (keys.contains("/ADBE")) {
                 have_extensions_adbe = true;
                 keys.erase("/ADBE");
             }
@@ -1807,12 +1807,12 @@ QPDFWriter::writeObject(QPDFObjectHandle object, int object_stream_index)
     indicateProgress(false, false);
     auto new_id = m->obj[old_og].renumber;
     if (m->qdf_mode) {
-        if (m->page_object_to_seq.count(old_og)) {
+        if (m->page_object_to_seq.contains(old_og)) {
             writeString("%% Page ");
             writeString(std::to_string(m->page_object_to_seq[old_og]));
             writeString("\n");
         }
-        if (m->contents_to_page_seq.count(old_og)) {
+        if (m->contents_to_page_seq.contains(old_og)) {
             writeString("%% Contents for page ");
             writeString(std::to_string(m->contents_to_page_seq[old_og]));
             writeString("\n");
diff --git a/libqpdf/QPDF_Dictionary.cc b/libqpdf/QPDF_Dictionary.cc
index e28d30a..d34d309 100644
--- a/libqpdf/QPDF_Dictionary.cc
+++ b/libqpdf/QPDF_Dictionary.cc
@@ -20,7 +20,7 @@ bool
 BaseDictionary::hasKey(std::string const& key) const
 {
     auto d = dict();
-    return d->items.count(key) > 0 && !d->items[key].isNull();
+    return d->items.contains(key) && !d->items[key].null();
 }
 
 QPDFObjectHandle
diff --git a/libqpdf/QPDF_json.cc b/libqpdf/QPDF_json.cc
index 81c5506..14f6693 100644
--- a/libqpdf/QPDF_json.cc
+++ b/libqpdf/QPDF_json.cc
@@ -889,7 +889,7 @@ QPDF::writeJSON(
     for (auto& obj: getAllObjects()) {
         auto const og = obj.getObjGen();
         std::string key = "obj:" + og.unparse(' ') + " R";
-        if (all_objects || wanted_objects.count(key)) {
+        if (all_objects || wanted_objects.contains(key)) {
             if (first) {
                 jw << "\n      \"" << key;
                 first = false;
@@ -911,7 +911,7 @@ QPDF::writeJSON(
             }
         }
     }
-    if (all_objects || wanted_objects.count("trailer")) {
+    if (all_objects || wanted_objects.contains("trailer")) {
         if (!first) {
             jw << "\n      },";
         }
diff --git a/libqpdf/QPDF_linearization.cc b/libqpdf/QPDF_linearization.cc
index 6519f6d..c9f0233 100644
--- a/libqpdf/QPDF_linearization.cc
+++ b/libqpdf/QPDF_linearization.cc
@@ -10,7 +10,7 @@
 #include <qpdf/Pl_Flate.hh>
 #include <qpdf/Pl_String.hh>
 #include <qpdf/QPDFExc.hh>
-#include <qpdf/QPDFLogger.hh>
+#include <qpdf/QPDFObjectHandle_private.hh>
 #include <qpdf/QPDFWriter_private.hh>
 #include <qpdf/QTC.hh>
 #include <qpdf/QUtil.hh>
@@ -502,7 +502,7 @@ QPDF::checkLinearizationInternal()
     qpdf_offset_t max_E = -1;
     for (auto const& oh: m->part6) {
         QPDFObjGen og(oh.getObjGen());
-        if (m->obj_cache.count(og) == 0) {
+        if (!m->obj_cache.contains(og)) {
             // All objects have to have been dereferenced to be classified.
             throw std::logic_error("linearization part6 object not in cache");
         }
@@ -530,12 +530,12 @@ QPDF::checkLinearizationInternal()
 qpdf_offset_t
 QPDF::maxEnd(ObjUser const& ou)
 {
-    if (m->obj_user_to_objects.count(ou) == 0) {
+    if (!m->obj_user_to_objects.contains(ou)) {
         stopOnError("no entry in object user table for requested object user");
     }
     qpdf_offset_t end = 0;
     for (auto const& og: m->obj_user_to_objects[ou]) {
-        if (!m->obj_cache.count(og)) {
+        if (!m->obj_cache.contains(og)) {
             stopOnError("unknown object referenced in object user table");
         }
         end = std::max(end, m->obj_cache[og].end_after_space);
@@ -568,7 +568,7 @@ QPDF::getLinearizationOffset(QPDFObjGen og)
 QPDFObjectHandle
 QPDF::getUncompressedObject(QPDFObjectHandle& obj, std::map<int, int> const& object_stream_data)
 {
-    if (obj.isNull() || (object_stream_data.count(obj.getObjectID()) == 0)) {
+    if (obj.null() || (!object_stream_data.contains(obj.getObjectID()))) {
         return obj;
     } else {
         int repl = (*(object_stream_data.find(obj.getObjectID()))).second;
@@ -593,11 +593,11 @@ QPDF::lengthNextN(int first_object, int n)
     int length = 0;
     for (int i = 0; i < n; ++i) {
         QPDFObjGen og(first_object + i, 0);
-        if (m->xref_table.count(og) == 0) {
+        if (!m->xref_table.contains(og)) {
             linearizationWarning(
                 "no xref table entry for " + std::to_string(first_object + i) + " 0");
         } else {
-            if (m->obj_cache.count(og) == 0) {
+            if (!m->obj_cache.contains(og)) {
                 stopOnError("found unknown object while calculating length for linearization data");
             }
             length += toI(m->obj_cache[og].end_after_space - getLinearizationOffset(og));
@@ -625,7 +625,7 @@ QPDF::checkHPageOffset(
     int npages = toI(pages.size());
     qpdf_offset_t table_offset = adjusted_offset(m->page_offset_hints.first_page_offset);
     QPDFObjGen first_page_og(pages.at(0).getObjGen());
-    if (m->xref_table.count(first_page_og) == 0) {
+    if (!m->xref_table.contains(first_page_og)) {
         stopOnError("supposed first page object is not known");
     }
     qpdf_offset_t offset = getLinearizationOffset(first_page_og);
@@ -636,7 +636,7 @@ QPDF::checkHPageOffset(
     for (int pageno = 0; pageno < npages; ++pageno) {
         QPDFObjGen page_og(pages.at(toS(pageno)).getObjGen());
         int first_object = page_og.getObj();
-        if (m->xref_table.count(page_og) == 0) {
+        if (!m->xref_table.contains(page_og)) {
             stopOnError("unknown object in page offset hint table");
         }
         offset = getLinearizationOffset(page_og);
@@ -677,7 +677,7 @@ QPDF::checkHPageOffset(
 
         for (size_t i = 0; i < toS(he.nshared_objects); ++i) {
             int idx = he.shared_identifiers.at(i);
-            if (shared_idx_to_obj.count(idx) == 0) {
+            if (!shared_idx_to_obj.contains(idx)) {
                 stopOnError("unable to get object for item in shared objects hint table");
             }
             hint_shared.insert(shared_idx_to_obj[idx]);
@@ -693,7 +693,7 @@ QPDF::checkHPageOffset(
         }
 
         for (int iter: hint_shared) {
-            if (!computed_shared.count(iter)) {
+            if (!computed_shared.contains(iter)) {
                 // pdlin puts thumbnails here even though it shouldn't
                 linearizationWarning(
                     "page " + std::to_string(pageno) + ": shared object " + std::to_string(iter) +
@@ -702,7 +702,7 @@ QPDF::checkHPageOffset(
         }
 
         for (int iter: computed_shared) {
-            if (!hint_shared.count(iter)) {
+            if (!hint_shared.contains(iter)) {
                 // Acrobat does not put some things including at least built-in fonts and procsets
                 // here, at least in some cases.
                 linearizationWarning(
@@ -755,7 +755,7 @@ QPDF::checkHSharedObject(std::vector<QPDFObjectHandle> const& pages, std::map<in
                 cur_object = so.first_shared_obj;
 
                 QPDFObjGen og(cur_object, 0);
-                if (m->xref_table.count(og) == 0) {
+                if (!m->xref_table.contains(og)) {
                     stopOnError("unknown object in shared object hint table");
                 }
                 qpdf_offset_t offset = getLinearizationOffset(og);
@@ -806,7 +806,7 @@ QPDF::checkHOutlines()
                 return;
             }
             QPDFObjGen og(outlines.getObjGen());
-            if (m->xref_table.count(og) == 0) {
+            if (!m->xref_table.contains(og)) {
                 stopOnError("unknown object in outlines hint table");
             }
             qpdf_offset_t offset = getLinearizationOffset(og);
@@ -1086,7 +1086,7 @@ QPDF::calculateLinearizationData(T const& object_stream_data)
                 break;
 
             case ObjUser::ou_root_key:
-                if (open_document_keys.count(ou.key) > 0) {
+                if (open_document_keys.contains(ou.key)) {
                     in_open_document = true;
                 } else if (ou.key == "/Outlines") {
                     in_outlines = true;
@@ -1187,7 +1187,7 @@ QPDF::calculateLinearizationData(T const& object_stream_data)
         stopOnError("no pages found while calculating linearization data");
     }
     QPDFObjGen first_page_og(pages.at(0).getObjGen());
-    if (!lc_first_page_private.count(first_page_og)) {
+    if (!lc_first_page_private.contains(first_page_og)) {
         stopOnError(
             "INTERNAL ERROR: QPDF::calculateLinearizationData: first page "
             "object not in lc_first_page_private");
@@ -1226,7 +1226,7 @@ QPDF::calculateLinearizationData(T const& object_stream_data)
         // Place this page's page object
 
         QPDFObjGen page_og(pages.at(i).getObjGen());
-        if (!lc_other_page_private.count(page_og)) {
+        if (!lc_other_page_private.contains(page_og)) {
             stopOnError(
                 "INTERNAL ERROR: QPDF::calculateLinearizationData: page object for page " +
                 std::to_string(i) + " not in lc_other_page_private");
@@ -1240,11 +1240,11 @@ QPDF::calculateLinearizationData(T const& object_stream_data)
         m->c_page_offset_data.entries.at(i).nobjects = 1;
 
         ObjUser ou(ObjUser::ou_page, toI(i));
-        if (m->obj_user_to_objects.count(ou) == 0) {
+        if (!m->obj_user_to_objects.contains(ou)) {
             stopOnError("found unreferenced page while calculating linearization data");
         }
         for (auto const& og: m->obj_user_to_objects[ou]) {
-            if (lc_other_page_private.count(og)) {
+            if (lc_other_page_private.contains(og)) {
                 lc_other_page_private.erase(og);
                 m->part7.push_back(getObject(og));
                 ++m->c_page_offset_data.entries.at(i).nobjects;
@@ -1279,7 +1279,7 @@ QPDF::calculateLinearizationData(T const& object_stream_data)
         stopOnError("found empty pages tree while calculating linearization data");
     }
     for (auto const& og: pages_ogs) {
-        if (lc_other.count(og)) {
+        if (lc_other.contains(og)) {
             lc_other.erase(og);
             m->part9.push_back(getObject(og));
         }
@@ -1293,7 +1293,7 @@ QPDF::calculateLinearizationData(T const& object_stream_data)
         if (!thumb.isNull()) {
             // Output the thumbnail itself
             QPDFObjGen thumb_og(thumb.getObjGen());
-            if (lc_thumbnail_private.count(thumb_og)) {
+            if (lc_thumbnail_private.contains(thumb_og)) {
                 lc_thumbnail_private.erase(thumb_og);
                 m->part9.push_back(thumb);
             } else {
@@ -1304,7 +1304,7 @@ QPDF::calculateLinearizationData(T const& object_stream_data)
             }
             std::set<QPDFObjGen>& ogs = m->obj_user_to_objects[ObjUser(ObjUser::ou_thumb, toI(i))];
             for (auto const& og: ogs) {
-                if (lc_thumbnail_private.count(og)) {
+                if (lc_thumbnail_private.contains(og)) {
                     lc_thumbnail_private.erase(og);
                     m->part9.push_back(getObject(og));
                 }
@@ -1384,11 +1384,11 @@ QPDF::calculateLinearizationData(T const& object_stream_data)
     for (size_t i = 1; i < toS(npages); ++i) {
         CHPageOffsetEntry& pe = m->c_page_offset_data.entries.at(i);
         ObjUser ou(ObjUser::ou_page, toI(i));
-        if (m->obj_user_to_objects.count(ou) == 0) {
+        if (!m->obj_user_to_objects.contains(ou)) {
             stopOnError("found unreferenced page while calculating linearization data");
         }
         for (auto const& og: m->obj_user_to_objects[ou]) {
-            if ((m->object_to_obj_users[og].size() > 1) && (obj_to_index.count(og.getObj()) > 0)) {
+            if ((m->object_to_obj_users[og].size() > 1) && (obj_to_index.contains(og.getObj()))) {
                 int idx = obj_to_index[og.getObj()];
                 ++pe.nshared_objects;
                 pe.shared_identifiers.push_back(idx);
diff --git a/libqpdf/QPDF_objects.cc b/libqpdf/QPDF_objects.cc
index 7ef8427..12ad916 100644
--- a/libqpdf/QPDF_objects.cc
+++ b/libqpdf/QPDF_objects.cc
@@ -442,7 +442,7 @@ QPDF::read_xref(qpdf_offset_t xref_offset, bool in_stream_recovery)
         } else {
             xref_offset = read_xrefStream(xref_offset, in_stream_recovery);
         }
-        if (visited.count(xref_offset) != 0) {
+        if (visited.contains(xref_offset)) {
             QTC::TC("qpdf", "QPDF xref loop");
             throw damagedPDF("", -1, "loop detected following xref tables");
         }
@@ -1020,7 +1020,7 @@ QPDF::insertXrefEntry(int obj, int f0, qpdf_offset_t f1, int f2)
         return;
     }
 
-    if (m->deleted_objects.count(obj)) {
+    if (m->deleted_objects.contains(obj)) {
         QTC::TC("qpdf", "QPDF xref deleted object");
         return;
     }
@@ -1056,7 +1056,7 @@ QPDF::insertXrefEntry(int obj, int f0, qpdf_offset_t f1, int f2)
 void
 QPDF::insertFreeXrefEntry(QPDFObjGen og)
 {
-    if (!m->xref_table.count(og)) {
+    if (!m->xref_table.contains(og)) {
         m->deleted_objects.insert(og.getObj());
     }
 }
@@ -1476,7 +1476,7 @@ QPDF::readObjectAtOffset(
         if (try_recovery) {
             // Try again after reconstructing xref table
             reconstruct_xref(e);
-            if (m->xref_table.count(exp_og) && (m->xref_table[exp_og].getType() == 1)) {
+            if (m->xref_table.contains(exp_og) && m->xref_table[exp_og].getType() == 1) {
                 qpdf_offset_t new_offset = m->xref_table[exp_og].getOffset();
                 QPDFObjectHandle result =
                     readObjectAtOffset(false, new_offset, description, exp_og, og, false);
@@ -1522,7 +1522,7 @@ QPDF::readObjectAtOffset(
             }
         }
         qpdf_offset_t end_after_space = m->file->tell();
-        if (skip_cache_if_in_xref && m->xref_table.count(og)) {
+        if (skip_cache_if_in_xref && m->xref_table.contains(og)) {
             // Ordinarily, an object gets read here when resolved through xref table or stream. In
             // the special case of the xref stream and linearization hint tables, the offset comes
             // from another source. For the specific case of xref streams, the xref stream is read
@@ -1564,7 +1564,7 @@ QPDF::resolve(QPDFObjGen og)
         return m->obj_cache[og].object;
     }
 
-    if (m->resolving.count(og)) {
+    if (m->resolving.contains(og)) {
         // This can happen if an object references itself directly or indirectly in some key that
         // has to be resolved during object parsing, such as stream length.
         QTC::TC("qpdf", "QPDF recursion loop in resolve");
@@ -1574,7 +1574,7 @@ QPDF::resolve(QPDFObjGen og)
     }
     ResolveRecorder rr(this, og);
 
-    if (m->xref_table.count(og) != 0) {
+    if (m->xref_table.contains(og)) {
         QPDFXRefEntry const& entry = m->xref_table[og];
         try {
             switch (entry.getType()) {
@@ -1628,7 +1628,7 @@ QPDF::resolveObjectsInStream(int obj_stream_number)
             true};
     };
 
-    if (m->resolved_object_streams.count(obj_stream_number)) {
+    if (m->resolved_object_streams.contains(obj_stream_number)) {
         return;
     }
     m->resolved_object_streams.insert(obj_stream_number);
@@ -1791,7 +1791,7 @@ QPDF::updateCache(
 bool
 QPDF::isCached(QPDFObjGen og)
 {
-    return m->obj_cache.count(og) != 0;
+    return m->obj_cache.contains(og);
 }
 
 bool
@@ -1835,7 +1835,7 @@ QPDF::getObjectForParser(int id, int gen, bool parse_pdf)
     if (auto iter = m->obj_cache.find(og); iter != m->obj_cache.end()) {
         return iter->second.object;
     }
-    if (m->xref_table.count(og) || !m->parsed) {
+    if (m->xref_table.contains(og) || !m->parsed) {
         return m->obj_cache.insert({og, QPDFObject::create<QPDF_Unresolved>(this, og)})
             .first->second.object;
     }
@@ -1852,7 +1852,7 @@ QPDF::getObjectForJSON(int id, int gen)
     auto [it, inserted] = m->obj_cache.try_emplace(og);
     auto& obj = it->second.object;
     if (inserted) {
-        obj = (m->parsed && !m->xref_table.count(og))
+        obj = (m->parsed && !m->xref_table.contains(og))
             ? QPDFObject::create<QPDF_Null>(this, og)
             : QPDFObject::create<QPDF_Unresolved>(this, og);
     }
@@ -1864,7 +1864,7 @@ QPDF::getObject(QPDFObjGen og)
 {
     if (auto it = m->obj_cache.find(og); it != m->obj_cache.end()) {
         return {it->second.object};
-    } else if (m->parsed && !m->xref_table.count(og)) {
+    } else if (m->parsed && !m->xref_table.contains(og)) {
         return QPDFObject::create<QPDF_Null>();
     } else {
         auto result =
diff --git a/libqpdf/QPDF_pages.cc b/libqpdf/QPDF_pages.cc
index f19539a..1b18981 100644
--- a/libqpdf/QPDF_pages.cc
+++ b/libqpdf/QPDF_pages.cc
@@ -303,7 +303,7 @@ QPDF::insertPage(QPDFObjectHandle newpage, int pos)
                                               : 2); // insert in middle
 
     auto og = newpage.getObjGen();
-    if (m->pageobj_to_pages_pos.count(og)) {
+    if (m->pageobj_to_pages_pos.contains(og)) {
         QTC::TC("qpdf", "QPDF resolve duplicated page in insert");
         newpage = makeIndirectObject(QPDFObjectHandle(newpage).shallowCopy());
     }
diff --git a/libqpdf/QTC.cc b/libqpdf/QTC.cc
index ae9649a..e69f2b7 100644
--- a/libqpdf/QTC.cc
+++ b/libqpdf/QTC.cc
@@ -39,7 +39,7 @@ QTC::TC_real(char const* const scope, char const* const ccase, int n)
     }
 #undef TC_ENV
 
-    if (cache.count(std::make_pair(ccase, n))) {
+    if (cache.contains(std::make_pair(ccase, n))) {
         return;
     }
     cache.insert(std::make_pair(ccase, n));
diff --git a/libqpdf/QUtil.cc b/libqpdf/QUtil.cc
index 05b53ba..19e85b4 100644
--- a/libqpdf/QUtil.cc
+++ b/libqpdf/QUtil.cc
@@ -1395,7 +1395,7 @@ QUtil::parse_numrange(char const* range, int max)
                 work = last_group;
                 last_group.clear();
                 for (auto n: work) {
-                    if (exclusions.count(n) == 0) {
+                    if (!exclusions.contains(n)) {
                         last_group.emplace_back(n);
                     }
                 }
@@ -1886,7 +1886,7 @@ QUtil::possible_repaired_encodings(std::string supplied)
     std::vector<std::string> t;
     std::set<std::string> seen;
     for (auto const& iter: result) {
-        if (!seen.count(iter)) {
+        if (!seen.contains(iter)) {
             seen.insert(iter);
             t.push_back(iter);
         }
@@ -1988,7 +1988,7 @@ QUtil::get_max_memory_usage()
                     attrs[m2->str(1)] = m2->str(2);
                 }
                 if (tag == "total") {
-                    if (attrs.count("size") > 0) {
+                    if (attrs.contains("size")) {
                         result += QIntC::to_size(QUtil::string_to_ull(attrs["size"].c_str()));
                     }
                 } else if (tag == "system" && attrs["type"] == "max") {
diff --git a/qpdf/test_driver.cc b/qpdf/test_driver.cc
index 4cb8882..14cf65f 100644
--- a/qpdf/test_driver.cc
+++ b/qpdf/test_driver.cc
@@ -3621,7 +3621,7 @@ runtest(int n, char const* filename1, char const* arg2)
             p[i] = static_cast<char>(p[i] ^ 0xcc);
         }
         pdf.processMemoryFile((std::string(filename1) + ".pdf").c_str(), p, size);
-    } else if (ignore_filename.count(n)) {
+    } else if (ignore_filename.contains(n)) {
         // Ignore filename argument entirely
     } else if (n == 89) {
         pdf.createFromJSON(filename1);
diff --git a/qpdf/test_parsedoffset.cc b/qpdf/test_parsedoffset.cc
index 0978bfc..f2b13b6 100644
--- a/qpdf/test_parsedoffset.cc
+++ b/qpdf/test_parsedoffset.cc
@@ -77,7 +77,7 @@ process(std::string fn, std::vector<std::vector<std::pair<qpdf_offset_t, std::st
     std::map<QPDFObjGen, QPDFXRefEntry> xrefs = qpdf.getXRefTable();
 
     for (auto const& oh: qpdf.getAllObjects()) {
-        if (xrefs.count(oh.getObjGen()) == 0) {
+        if (!xrefs.contains(oh.getObjGen())) {
             std::cerr << oh.getObjectID() << "/" << oh.getGeneration()
                       << " is not found in xref table" << std::endl;
             std::exit(2);
diff --git a/qpdf/test_renumber.cc b/qpdf/test_renumber.cc
index 3eaa889..33127f1 100644
--- a/qpdf/test_renumber.cc
+++ b/qpdf/test_renumber.cc
@@ -26,7 +26,7 @@ compare(QPDFObjectHandle a, QPDFObjectHandle b)
 {
     static std::set<QPDFObjGen> visited;
     if (a.isIndirect()) {
-        if (visited.count(a.getObjGen())) {
+        if (visited.contains(a.getObjGen())) {
             return true;
         }
         visited.insert(a.getObjGen());
@@ -128,7 +128,7 @@ compare_xref_table(std::map<QPDFObjGen, QPDFXRefEntry> a, std::map<QPDFObjGen, Q
         std::cout << "xref entry for " << iter.first.getObj() << "/" << iter.first.getGen()
                   << std::endl;
 
-        if (b.count(iter.first) == 0) {
+        if (!b.contains(iter.first)) {
             std::cerr << "not found" << std::endl;
             return false;
         }