diff --git a/examples/pdf-mod-info.cc b/examples/pdf-mod-info.cc
index e97fab9..c9fffa6 100644
--- a/examples/pdf-mod-info.cc
+++ b/examples/pdf-mod-info.cc
@@ -90,11 +90,11 @@ main(int argc, char* argv[])
         } else if ((!strcmp(argv[i], "--key")) && (++i < argc)) {
             QTC::TC("examples", "pdf-mod-info -key");
             cur_key = argv[i];
-            if (!((cur_key.length() > 0) && (cur_key.at(0) == '/'))) {
+            if (cur_key.empty() || cur_key.at(0) != '/') {
                 cur_key = "/" + cur_key;
             }
             Keys[cur_key] = "";
-        } else if ((!strcmp(argv[i], "--val")) && (++i < argc)) {
+        } else if (!strcmp(argv[i], "--val") && ++i < argc) {
             if (cur_key.empty()) {
                 QTC::TC("examples", "pdf-mod-info usage wrong val");
                 usage();
@@ -115,7 +115,7 @@ main(int argc, char* argv[])
         QTC::TC("examples", "pdf-mod-info in-place");
         fl_out = fl_in;
     }
-    if (Keys.size() == 0) {
+    if (Keys.empty()) {
         QTC::TC("examples", "pdf-mod-info no keys");
         usage();
     }
@@ -141,7 +141,7 @@ main(int argc, char* argv[])
                     filetrailer.replaceKey("/Info", fileinfo);
                 }
             }
-            if (it.second == "") {
+            if (it.second.empty()) {
                 fileinfo.removeKey(it.first);
             } else {
                 QPDFObjectHandle elt = fileinfo.newString(it.second);
diff --git a/libqpdf/QPDFAcroFormDocumentHelper.cc b/libqpdf/QPDFAcroFormDocumentHelper.cc
index 46e87c9..5c513c3 100644
--- a/libqpdf/QPDFAcroFormDocumentHelper.cc
+++ b/libqpdf/QPDFAcroFormDocumentHelper.cc
@@ -675,7 +675,7 @@ QPDFAcroFormDocumentHelper::adjustAppearanceStream(
     resources.mergeResources(merge_with, &dr_map);
     // Remove empty subdictionaries
     for (auto iter: resources.ditems()) {
-        if (iter.second.isDictionary() && (iter.second.getKeys().size() == 0)) {
+        if (iter.second.isDictionary() && iter.second.getKeys().empty()) {
             resources.removeKey(iter.first);
         }
     }
diff --git a/libqpdf/QPDFArgParser.cc b/libqpdf/QPDFArgParser.cc
index 08e727c..e1cdfe8 100644
--- a/libqpdf/QPDFArgParser.cc
+++ b/libqpdf/QPDFArgParser.cc
@@ -471,7 +471,7 @@ QPDFArgParser::parseArgs()
             // positional arguments. Besides, it doesn't make sense to have an empty option.
             arg_s = arg;
             size_t equal_pos = std::string::npos;
-            if (arg_s.length() > 0) {
+            if (!arg_s.empty()) {
                 equal_pos = arg_s.find('=', 1);
             }
             if (equal_pos != std::string::npos) {
@@ -686,7 +686,7 @@ QPDFArgParser::addHelpTopic(
         QTC::TC("libtests", "QPDFArgParser add reserved help topic");
         throw std::logic_error("QPDFArgParser: can't register reserved help topic " + topic);
     }
-    if (!((topic.length() > 0) && (topic.at(0) != '-'))) {
+    if (topic.empty() || topic.at(0) == '-') {
         QTC::TC("libtests", "QPDFArgParser bad topic for help");
         throw std::logic_error("QPDFArgParser: help topics must not start with -");
     }
diff --git a/libqpdf/QPDFJob.cc b/libqpdf/QPDFJob.cc
index 1a74ea4..9f762d7 100644
--- a/libqpdf/QPDFJob.cc
+++ b/libqpdf/QPDFJob.cc
@@ -396,7 +396,7 @@ QPDFJob::parseRotationParameter(std::string const& parameter)
     } else {
         angle_str = parameter;
     }
-    if (angle_str.length() > 0) {
+    if (!angle_str.empty()) {
         char first = angle_str.at(0);
         if ((first == '+') || (first == '-')) {
             relative = ((first == '+') ? 1 : -1);
diff --git a/libqpdf/QPDFJob_config.cc b/libqpdf/QPDFJob_config.cc
index 2aff98c..2eca88e 100644
--- a/libqpdf/QPDFJob_config.cc
+++ b/libqpdf/QPDFJob_config.cc
@@ -696,7 +696,7 @@ QPDFJob::Config::passwordFile(std::string const& parameter)
         QTC::TC("qpdf", "QPDFJob_config password file");
         lines = QUtil::read_lines_from_file(parameter.c_str());
     }
-    if (lines.size() >= 1) {
+    if (!lines.empty()) {
         o.m->password = QUtil::make_shared_cstr(lines.front());
 
         if (lines.size() > 1) {
diff --git a/libqpdf/QPDFObjectHandle.cc b/libqpdf/QPDFObjectHandle.cc
index fba9cbc..f0baa22 100644
--- a/libqpdf/QPDFObjectHandle.cc
+++ b/libqpdf/QPDFObjectHandle.cc
@@ -467,7 +467,7 @@ BaseHandle::write_json(int json_version, JSON::Writer& p) const
     case ::ot_real:
         {
             auto const& val = std::get<QPDF_Real>(obj->value).val;
-            if (val.length() == 0) {
+            if (val.empty()) {
                 // Can't really happen...
                 p << "0";
             } else if (val.at(0) == '.') {
diff --git a/libqpdf/QPDFWriter.cc b/libqpdf/QPDFWriter.cc
index de7227d..4802543 100644
--- a/libqpdf/QPDFWriter.cc
+++ b/libqpdf/QPDFWriter.cc
@@ -271,7 +271,7 @@ void
 QPDFWriter::setExtraHeaderText(std::string const& text)
 {
     m->extra_header_text = text;
-    if ((m->extra_header_text.length() > 0) && (*(m->extra_header_text.rbegin()) != '\n')) {
+    if (!m->extra_header_text.empty() && *m->extra_header_text.rbegin() != '\n') {
         QTC::TC("qpdf", "QPDFWriter extra header text add newline");
         m->extra_header_text += "\n";
     } else {
@@ -1419,7 +1419,7 @@ QPDFWriter::unparseObject(
                 have_extensions_adbe = true;
                 keys.erase("/ADBE");
             }
-            if (keys.size() > 0) {
+            if (!keys.empty()) {
                 have_extensions_other = true;
             }
         }
diff --git a/libqpdf/QPDF_json.cc b/libqpdf/QPDF_json.cc
index 14f6693..3c3d86b 100644
--- a/libqpdf/QPDF_json.cc
+++ b/libqpdf/QPDF_json.cc
@@ -192,7 +192,7 @@ QPDF::test_json_validators()
     check(is_unicode_string("u:potato", str));
     check(str == "potato");
     check(is_unicode_string("u:", str));
-    check(str == "");
+    check(str.empty());
     check(!is_binary_string("", str));
     check(!is_binary_string("x:", str));
     check(!is_binary_string("b:1", str));
diff --git a/libqpdf/QPDF_objects.cc b/libqpdf/QPDF_objects.cc
index 12ad916..3e1f08c 100644
--- a/libqpdf/QPDF_objects.cc
+++ b/libqpdf/QPDF_objects.cc
@@ -153,7 +153,7 @@ QPDF::parse(char const* password)
 
     initializeEncryption();
     m->parsed = true;
-    if (m->xref_table.size() > 0 && !getRoot().getKey("/Pages").isDictionary()) {
+    if (!m->xref_table.empty() && !getRoot().getKey("/Pages").isDictionary()) {
         // QPDFs created from JSON have an empty xref table and no root object yet.
         throw damagedPDF("", -1, "unable to find page tree");
     }
@@ -1932,8 +1932,8 @@ QPDF::tableSize()
 {
     // If obj_cache is dense, accommodate all object in tables,else accommodate only original
     // objects.
-    auto max_xref = m->xref_table.size() ? m->xref_table.crbegin()->first.getObj() : 0;
-    auto max_obj = m->obj_cache.size() ? m->obj_cache.crbegin()->first.getObj() : 0;
+    auto max_xref = !m->xref_table.empty() ? m->xref_table.crbegin()->first.getObj() : 0;
+    auto max_obj = !m->obj_cache.empty() ? m->obj_cache.crbegin()->first.getObj() : 0;
     auto max_id = std::numeric_limits<int>::max() - 1;
     if (max_obj >= max_id || max_xref >= max_id) {
         // Temporary fix. Long-term solution is
diff --git a/qpdf/test_driver.cc b/qpdf/test_driver.cc
index 14cf65f..445a38f 100644
--- a/qpdf/test_driver.cc
+++ b/qpdf/test_driver.cc
@@ -1442,7 +1442,7 @@ test_42(QPDF& pdf, char const* arg2)
         assert(i == di.end());
         assert(!i_value.second);
     }
-    assert("" == qtest.getStringValue());
+    assert(qtest.getStringValue().empty());
     array.getArrayItem(-1).assertNull();
     array.getArrayItem(16059).assertNull();
     integer.getArrayItem(0).assertNull();
@@ -3111,7 +3111,7 @@ test_87(QPDF& pdf, char const* arg2)
     assert(dict.getKeys() == std::set<std::string>({"/A"}));
     dict.replaceKey("/A", QPDFObjectHandle::newNull());
     assert(dict.unparse() == "<< >>");
-    assert(dict.getKeys() == std::set<std::string>());
+    assert(dict.getKeys().empty());
     dict = QPDFObjectHandle::newDictionary({
         {"/A", "2"_qpdf},
         {"/B", QPDFObjectHandle::newNull()},
diff --git a/qpdf/test_parsedoffset.cc b/qpdf/test_parsedoffset.cc
index f2b13b6..4721e12 100644
--- a/qpdf/test_parsedoffset.cc
+++ b/qpdf/test_parsedoffset.cc
@@ -120,7 +120,7 @@ main(int argc, char* argv[])
         process(argv[1], table);
 
         for (size_t i = 0; i < table.size(); ++i) {
-            if (table[i].size() == 0) {
+            if (table[i].empty()) {
                 continue;
             }