diff --git a/examples/pdf-bookmarks.cc b/examples/pdf-bookmarks.cc
index b6f87e4..d507f55 100644
--- a/examples/pdf-bookmarks.cc
+++ b/examples/pdf-bookmarks.cc
@@ -5,8 +5,8 @@
 #include <qpdf/QTC.hh>
 #include <qpdf/QUtil.hh>
 #include <iostream>
-#include <stdlib.h>
-#include <string.h>
+#include <cstdlib>
+#include <cstring>
 
 // This program demonstrates extraction of bookmarks using the qpdf
 // outlines API. Note that all the information shown by this program
diff --git a/examples/pdf-count-strings.cc b/examples/pdf-count-strings.cc
index 09c4a1f..584d630 100644
--- a/examples/pdf-count-strings.cc
+++ b/examples/pdf-count-strings.cc
@@ -5,7 +5,7 @@
 //
 
 #include <iostream>
-#include <stdlib.h>
+#include <cstdlib>
 
 #include <qpdf/Pl_StdioFile.hh>
 #include <qpdf/QPDF.hh>
diff --git a/examples/pdf-create.cc b/examples/pdf-create.cc
index 56af4a8..7898479 100644
--- a/examples/pdf-create.cc
+++ b/examples/pdf-create.cc
@@ -16,7 +16,7 @@
 #include <qpdf/QUtil.hh>
 #include <iostream>
 #include <memory>
-#include <stdlib.h>
+#include <cstdlib>
 
 static char const* whoami = nullptr;
 
diff --git a/examples/pdf-double-page-size.cc b/examples/pdf-double-page-size.cc
index 1ebe71d..d1fb334 100644
--- a/examples/pdf-double-page-size.cc
+++ b/examples/pdf-double-page-size.cc
@@ -5,8 +5,8 @@
 #include <qpdf/QPDFWriter.hh>
 #include <qpdf/QUtil.hh>
 #include <iostream>
-#include <stdlib.h>
-#include <string.h>
+#include <cstdlib>
+#include <cstring>
 
 static char const* whoami = nullptr;
 
diff --git a/examples/pdf-filter-tokens.cc b/examples/pdf-filter-tokens.cc
index 8824b39..173feb6 100644
--- a/examples/pdf-filter-tokens.cc
+++ b/examples/pdf-filter-tokens.cc
@@ -8,7 +8,7 @@
 #include <algorithm>
 #include <deque>
 #include <iostream>
-#include <stdlib.h>
+#include <cstdlib>
 
 #include <qpdf/QPDF.hh>
 #include <qpdf/QPDFObjectHandle.hh>
diff --git a/examples/pdf-invert-images.cc b/examples/pdf-invert-images.cc
index 9ffb9c1..06d7419 100644
--- a/examples/pdf-invert-images.cc
+++ b/examples/pdf-invert-images.cc
@@ -6,8 +6,8 @@
 #include <qpdf/QPDFWriter.hh>
 #include <qpdf/QUtil.hh>
 #include <iostream>
-#include <stdlib.h>
-#include <string.h>
+#include <cstdlib>
+#include <cstring>
 
 static char const* whoami = nullptr;
 
diff --git a/examples/pdf-mod-info.cc b/examples/pdf-mod-info.cc
index fa49738..196ce97 100644
--- a/examples/pdf-mod-info.cc
+++ b/examples/pdf-mod-info.cc
@@ -6,9 +6,9 @@
 #include <qpdf/QTC.hh>
 #include <qpdf/QUtil.hh>
 #include <iostream>
-#include <stdio.h>
-#include <stdlib.h>
-#include <string.h>
+#include <cstdio>
+#include <cstdlib>
+#include <cstring>
 
 static char const* version = "1.1";
 static char const* whoami = nullptr;
diff --git a/examples/pdf-npages.cc b/examples/pdf-npages.cc
index 3d34d48..e98d136 100644
--- a/examples/pdf-npages.cc
+++ b/examples/pdf-npages.cc
@@ -1,6 +1,6 @@
 #include <iostream>
-#include <stdlib.h>
-#include <string.h>
+#include <cstdlib>
+#include <cstring>
 
 #include <qpdf/QPDF.hh>
 #include <qpdf/QUtil.hh>
diff --git a/examples/pdf-overlay-page.cc b/examples/pdf-overlay-page.cc
index d40bf0e..5c7bf46 100644
--- a/examples/pdf-overlay-page.cc
+++ b/examples/pdf-overlay-page.cc
@@ -4,7 +4,7 @@
 #include <qpdf/QPDFWriter.hh>
 #include <qpdf/QUtil.hh>
 #include <iostream>
-#include <stdlib.h>
+#include <cstdlib>
 
 // This program demonstrates use of form XObjects to overlay a page
 // from one file onto all pages of another file. The qpdf program's
diff --git a/examples/pdf-parse-content.cc b/examples/pdf-parse-content.cc
index 85abcab..4944041 100644
--- a/examples/pdf-parse-content.cc
+++ b/examples/pdf-parse-content.cc
@@ -1,5 +1,5 @@
 #include <iostream>
-#include <stdlib.h>
+#include <cstdlib>
 
 #include <qpdf/QIntC.hh>
 #include <qpdf/QPDF.hh>
diff --git a/examples/pdf-set-form-values.cc b/examples/pdf-set-form-values.cc
index 281e139..d13f060 100644
--- a/examples/pdf-set-form-values.cc
+++ b/examples/pdf-set-form-values.cc
@@ -4,7 +4,7 @@
 #include <qpdf/QPDFWriter.hh>
 #include <qpdf/QUtil.hh>
 #include <iostream>
-#include <stdlib.h>
+#include <cstdlib>
 
 static char const* whoami = nullptr;
 
diff --git a/examples/pdf-split-pages.cc b/examples/pdf-split-pages.cc
index 5d65853..6a4f149 100644
--- a/examples/pdf-split-pages.cc
+++ b/examples/pdf-split-pages.cc
@@ -12,7 +12,7 @@
 
 #include <cstring>
 #include <iostream>
-#include <stdlib.h>
+#include <cstdlib>
 #include <string>
 
 static bool static_id = false;
diff --git a/include/qpdf/Buffer.hh b/include/qpdf/Buffer.hh
index c5d55da..06615e2 100644
--- a/include/qpdf/Buffer.hh
+++ b/include/qpdf/Buffer.hh
@@ -26,7 +26,7 @@
 #include <qpdf/PointerHolder.hh> // unused -- remove in qpdf 12 (see #785)
 
 #include <memory>
-#include <stddef.h>
+#include <cstddef>
 
 class Buffer
 {
diff --git a/include/qpdf/InputSource.hh b/include/qpdf/InputSource.hh
index 68a787c..c66066f 100644
--- a/include/qpdf/InputSource.hh
+++ b/include/qpdf/InputSource.hh
@@ -27,7 +27,7 @@
 #include <qpdf/Types.h>
 
 #include <memory>
-#include <stdio.h>
+#include <cstdio>
 #include <string>
 
 // Remember to use QPDF_DLL_CLASS on anything derived from InputSource
diff --git a/include/qpdf/Pl_StdioFile.hh b/include/qpdf/Pl_StdioFile.hh
index 1508af2..d175d3c 100644
--- a/include/qpdf/Pl_StdioFile.hh
+++ b/include/qpdf/Pl_StdioFile.hh
@@ -26,7 +26,7 @@
 
 #include <qpdf/Pipeline.hh>
 
-#include <stdio.h>
+#include <cstdio>
 
 //
 // This pipeline is reusable.
diff --git a/include/qpdf/QPDF.hh b/include/qpdf/QPDF.hh
index 4541db6..5567a68 100644
--- a/include/qpdf/QPDF.hh
+++ b/include/qpdf/QPDF.hh
@@ -30,7 +30,7 @@
 #include <list>
 #include <map>
 #include <memory>
-#include <stdio.h>
+#include <cstdio>
 #include <string>
 #include <string_view>
 #include <vector>
diff --git a/include/qpdf/QPDFTokenizer.hh b/include/qpdf/QPDFTokenizer.hh
index 79d0d3c..4de7a63 100644
--- a/include/qpdf/QPDFTokenizer.hh
+++ b/include/qpdf/QPDFTokenizer.hh
@@ -28,7 +28,7 @@
 #include <qpdf/PointerHolder.hh> // unused -- remove in qpdf 12 (see #785)
 
 #include <memory>
-#include <stdio.h>
+#include <cstdio>
 #include <string>
 
 class QPDFTokenizer
diff --git a/include/qpdf/QPDFWriter.hh b/include/qpdf/QPDFWriter.hh
index c289620..15b5579 100644
--- a/include/qpdf/QPDFWriter.hh
+++ b/include/qpdf/QPDFWriter.hh
@@ -34,7 +34,7 @@
 #include <map>
 #include <memory>
 #include <set>
-#include <stdio.h>
+#include <cstdio>
 #include <string>
 #include <string_view>
 #include <vector>
diff --git a/include/qpdf/QUtil.hh b/include/qpdf/QUtil.hh
index 4d46f63..5291fe0 100644
--- a/include/qpdf/QUtil.hh
+++ b/include/qpdf/QUtil.hh
@@ -30,9 +30,9 @@
 #include <list>
 #include <memory>
 #include <stdexcept>
-#include <stdio.h>
+#include <cstdio>
 #include <string>
-#include <time.h>
+#include <ctime>
 #include <vector>
 
 class RandomDataProvider;
diff --git a/include/qpdf/RandomDataProvider.hh b/include/qpdf/RandomDataProvider.hh
index 5023b4d..d40bd1f 100644
--- a/include/qpdf/RandomDataProvider.hh
+++ b/include/qpdf/RandomDataProvider.hh
@@ -23,7 +23,7 @@
 #define RANDOMDATAPROVIDER_HH
 
 #include <qpdf/DLL.h>
-#include <string.h> // for size_t
+#include <cstring> // for size_t
 
 class QPDF_DLL_CLASS RandomDataProvider
 {
diff --git a/libqpdf/BufferInputSource.cc b/libqpdf/BufferInputSource.cc
index 005692a..33ab44f 100644
--- a/libqpdf/BufferInputSource.cc
+++ b/libqpdf/BufferInputSource.cc
@@ -3,7 +3,7 @@
 #include <qpdf/QIntC.hh>
 #include <algorithm>
 #include <sstream>
-#include <string.h>
+#include <cstring>
 
 BufferInputSource::BufferInputSource(
     std::string const& description, Buffer* buf, bool own_memory) :
diff --git a/libqpdf/FileInputSource.cc b/libqpdf/FileInputSource.cc
index 7c4d6d4..a5f0f4f 100644
--- a/libqpdf/FileInputSource.cc
+++ b/libqpdf/FileInputSource.cc
@@ -3,7 +3,7 @@
 #include <qpdf/QPDFExc.hh>
 #include <qpdf/QUtil.hh>
 #include <algorithm>
-#include <string.h>
+#include <cstring>
 
 FileInputSource::FileInputSource() :
     close_file(false),
diff --git a/libqpdf/InputSource.cc b/libqpdf/InputSource.cc
index 33ab44d..3a4bb88 100644
--- a/libqpdf/InputSource.cc
+++ b/libqpdf/InputSource.cc
@@ -3,7 +3,7 @@
 #include <qpdf/QIntC.hh>
 #include <qpdf/QTC.hh>
 #include <stdexcept>
-#include <string.h>
+#include <cstring>
 
 void
 InputSource::setLastOffset(qpdf_offset_t offset)
diff --git a/libqpdf/InsecureRandomDataProvider.cc b/libqpdf/InsecureRandomDataProvider.cc
index cb67cad..90a548e 100644
--- a/libqpdf/InsecureRandomDataProvider.cc
+++ b/libqpdf/InsecureRandomDataProvider.cc
@@ -2,7 +2,7 @@
 
 #include <qpdf/QUtil.hh>
 #include <qpdf/qpdf-config.h>
-#include <stdlib.h>
+#include <cstdlib>
 
 InsecureRandomDataProvider::InsecureRandomDataProvider() :
     seeded_random(false)
diff --git a/libqpdf/MD5.cc b/libqpdf/MD5.cc
index 5741937..9668c98 100644
--- a/libqpdf/MD5.cc
+++ b/libqpdf/MD5.cc
@@ -4,7 +4,7 @@
 #include <qpdf/QPDFCryptoProvider.hh>
 #include <qpdf/QUtil.hh>
 
-#include <string.h>
+#include <cstring>
 
 MD5::MD5()
 {
diff --git a/libqpdf/Pl_ASCII85Decoder.cc b/libqpdf/Pl_ASCII85Decoder.cc
index 1e3d1b4..e43b4a8 100644
--- a/libqpdf/Pl_ASCII85Decoder.cc
+++ b/libqpdf/Pl_ASCII85Decoder.cc
@@ -2,7 +2,7 @@
 
 #include <qpdf/QTC.hh>
 #include <stdexcept>
-#include <string.h>
+#include <cstring>
 
 Pl_ASCII85Decoder::Pl_ASCII85Decoder(char const* identifier, Pipeline* next) :
     Pipeline(identifier, next),
diff --git a/libqpdf/Pl_ASCIIHexDecoder.cc b/libqpdf/Pl_ASCIIHexDecoder.cc
index 48836f5..5590efb 100644
--- a/libqpdf/Pl_ASCIIHexDecoder.cc
+++ b/libqpdf/Pl_ASCIIHexDecoder.cc
@@ -1,7 +1,7 @@
 #include <qpdf/Pl_ASCIIHexDecoder.hh>
 
 #include <qpdf/QTC.hh>
-#include <ctype.h>
+#include <cctype>
 #include <stdexcept>
 
 Pl_ASCIIHexDecoder::Pl_ASCIIHexDecoder(char const* identifier, Pipeline* next) :
diff --git a/libqpdf/Pl_Buffer.cc b/libqpdf/Pl_Buffer.cc
index ca29ef6..d942465 100644
--- a/libqpdf/Pl_Buffer.cc
+++ b/libqpdf/Pl_Buffer.cc
@@ -2,8 +2,8 @@
 
 #include <algorithm>
 #include <stdexcept>
-#include <stdlib.h>
-#include <string.h>
+#include <cstdlib>
+#include <cstring>
 
 Pl_Buffer::Pl_Buffer(char const* identifier, Pipeline* next) :
     Pipeline(identifier, next),
diff --git a/libqpdf/Pl_DCT.cc b/libqpdf/Pl_DCT.cc
index 3558787..c01398a 100644
--- a/libqpdf/Pl_DCT.cc
+++ b/libqpdf/Pl_DCT.cc
@@ -3,7 +3,7 @@
 #include <qpdf/QIntC.hh>
 #include <qpdf/QTC.hh>
 
-#include <setjmp.h>
+#include <csetjmp>
 #include <stdexcept>
 #include <string>
 
diff --git a/libqpdf/Pl_Flate.cc b/libqpdf/Pl_Flate.cc
index 61873ff..6bbcd1b 100644
--- a/libqpdf/Pl_Flate.cc
+++ b/libqpdf/Pl_Flate.cc
@@ -1,7 +1,7 @@
 #include <qpdf/Pl_Flate.hh>
 
-#include <limits.h>
-#include <string.h>
+#include <climits>
+#include <cstring>
 #include <zlib.h>
 
 #include <qpdf/QIntC.hh>
diff --git a/libqpdf/Pl_LZWDecoder.cc b/libqpdf/Pl_LZWDecoder.cc
index 000fb64..1c2d680 100644
--- a/libqpdf/Pl_LZWDecoder.cc
+++ b/libqpdf/Pl_LZWDecoder.cc
@@ -4,7 +4,7 @@
 #include <qpdf/QTC.hh>
 #include <qpdf/QUtil.hh>
 #include <stdexcept>
-#include <string.h>
+#include <cstring>
 
 Pl_LZWDecoder::Pl_LZWDecoder(
     char const* identifier, Pipeline* next, bool early_code_change) :
diff --git a/libqpdf/Pl_PNGFilter.cc b/libqpdf/Pl_PNGFilter.cc
index e2a9a0d..41088e1 100644
--- a/libqpdf/Pl_PNGFilter.cc
+++ b/libqpdf/Pl_PNGFilter.cc
@@ -3,9 +3,9 @@
 #include <qpdf/QTC.hh>
 #include <qpdf/QUtil.hh>
 
-#include <limits.h>
+#include <climits>
 #include <stdexcept>
-#include <string.h>
+#include <cstring>
 
 static int
 abs_diff(int a, int b)
diff --git a/libqpdf/Pl_StdioFile.cc b/libqpdf/Pl_StdioFile.cc
index dca16bf..b83d0a9 100644
--- a/libqpdf/Pl_StdioFile.cc
+++ b/libqpdf/Pl_StdioFile.cc
@@ -3,7 +3,7 @@
 #include <qpdf/Pl_StdioFile.hh>
 
 #include <qpdf/QUtil.hh>
-#include <errno.h>
+#include <cerrno>
 #include <stdexcept>
 
 Pl_StdioFile::Members::Members(FILE* f) :
diff --git a/libqpdf/Pl_TIFFPredictor.cc b/libqpdf/Pl_TIFFPredictor.cc
index c29396d..45b6d39 100644
--- a/libqpdf/Pl_TIFFPredictor.cc
+++ b/libqpdf/Pl_TIFFPredictor.cc
@@ -5,9 +5,9 @@
 #include <qpdf/QTC.hh>
 #include <qpdf/QUtil.hh>
 
-#include <limits.h>
+#include <climits>
 #include <stdexcept>
-#include <string.h>
+#include <cstring>
 #include <vector>
 
 Pl_TIFFPredictor::Pl_TIFFPredictor(
diff --git a/libqpdf/QPDF.cc b/libqpdf/QPDF.cc
index c7cc137..bc88b5d 100644
--- a/libqpdf/QPDF.cc
+++ b/libqpdf/QPDF.cc
@@ -9,8 +9,8 @@
 #include <memory.h>
 #include <regex>
 #include <sstream>
-#include <stdlib.h>
-#include <string.h>
+#include <cstdlib>
+#include <cstring>
 #include <vector>
 
 #include <qpdf/BufferInputSource.hh>
diff --git a/libqpdf/QPDFFormFieldObjectHelper.cc b/libqpdf/QPDFFormFieldObjectHelper.cc
index e76e312..93dc0e6 100644
--- a/libqpdf/QPDFFormFieldObjectHelper.cc
+++ b/libqpdf/QPDFFormFieldObjectHelper.cc
@@ -6,7 +6,7 @@
 #include <qpdf/QPDFAnnotationObjectHelper.hh>
 #include <qpdf/QTC.hh>
 #include <qpdf/QUtil.hh>
-#include <stdlib.h>
+#include <cstdlib>
 
 QPDFFormFieldObjectHelper::QPDFFormFieldObjectHelper(QPDFObjectHandle oh) :
     QPDFObjectHelper(oh),
diff --git a/libqpdf/QPDFJob.cc b/libqpdf/QPDFJob.cc
index fbaa53e..1458310 100644
--- a/libqpdf/QPDFJob.cc
+++ b/libqpdf/QPDFJob.cc
@@ -3,7 +3,7 @@
 #include <cstdio>
 #include <cstdlib>
 #include <cstring>
-#include <ctype.h>
+#include <cctype>
 #include <fcntl.h>
 #include <iostream>
 #include <memory>
diff --git a/libqpdf/QPDFJob_argv.cc b/libqpdf/QPDFJob_argv.cc
index 55696f5..5534cd3 100644
--- a/libqpdf/QPDFJob_argv.cc
+++ b/libqpdf/QPDFJob_argv.cc
@@ -3,12 +3,12 @@
 // See "HOW TO ADD A COMMAND-LINE ARGUMENT" in README-maintainer.
 
 #include <cstdio>
-#include <ctype.h>
+#include <cctype>
 #include <iostream>
 #include <memory>
 #include <sstream>
-#include <stdlib.h>
-#include <string.h>
+#include <cstdlib>
+#include <cstring>
 
 #include <qpdf/QIntC.hh>
 #include <qpdf/QPDFArgParser.hh>
diff --git a/libqpdf/QPDFObjectHandle.cc b/libqpdf/QPDFObjectHandle.cc
index b3f208a..e276bf4 100644
--- a/libqpdf/QPDFObjectHandle.cc
+++ b/libqpdf/QPDFObjectHandle.cc
@@ -30,10 +30,10 @@
 
 #include <algorithm>
 #include <cstring>
-#include <ctype.h>
-#include <limits.h>
+#include <cctype>
+#include <climits>
 #include <stdexcept>
-#include <stdlib.h>
+#include <cstdlib>
 
 using namespace std::literals;
 
diff --git a/libqpdf/QPDFSystemError.cc b/libqpdf/QPDFSystemError.cc
index 65fa312..ebd0d77 100644
--- a/libqpdf/QPDFSystemError.cc
+++ b/libqpdf/QPDFSystemError.cc
@@ -1,6 +1,6 @@
 #include <qpdf/QPDFSystemError.hh>
 
-#include <string.h>
+#include <cstring>
 
 QPDFSystemError::QPDFSystemError(
     std::string const& description, int system_errno) :
diff --git a/libqpdf/QPDFTokenizer.cc b/libqpdf/QPDFTokenizer.cc
index d8d457a..d83080b 100644
--- a/libqpdf/QPDFTokenizer.cc
+++ b/libqpdf/QPDFTokenizer.cc
@@ -11,8 +11,8 @@
 #include <qpdf/QUtil.hh>
 
 #include <stdexcept>
-#include <stdlib.h>
-#include <string.h>
+#include <cstdlib>
+#include <cstring>
 
 static inline bool
 is_delimiter(char ch)
diff --git a/libqpdf/QPDFWriter.cc b/libqpdf/QPDFWriter.cc
index de1aa45..56b4e1e 100644
--- a/libqpdf/QPDFWriter.cc
+++ b/libqpdf/QPDFWriter.cc
@@ -24,7 +24,7 @@
 
 #include <algorithm>
 #include <stdexcept>
-#include <stdlib.h>
+#include <cstdlib>
 
 QPDFWriter::ProgressReporter::~ProgressReporter()
 {
diff --git a/libqpdf/QPDF_encryption.cc b/libqpdf/QPDF_encryption.cc
index 2e5ddef..64ca10f 100644
--- a/libqpdf/QPDF_encryption.cc
+++ b/libqpdf/QPDF_encryption.cc
@@ -17,7 +17,7 @@
 #include <qpdf/RC4.hh>
 
 #include <algorithm>
-#include <string.h>
+#include <cstring>
 
 static unsigned char const padding_string[] = {
     0x28, 0xbf, 0x4e, 0x5e, 0x4e, 0x75, 0x8a, 0x41, 0x64, 0x00, 0x4e,
diff --git a/libqpdf/QPDF_linearization.cc b/libqpdf/QPDF_linearization.cc
index 5b72943..eade317 100644
--- a/libqpdf/QPDF_linearization.cc
+++ b/libqpdf/QPDF_linearization.cc
@@ -13,8 +13,8 @@
 #include <qpdf/QUtil.hh>
 
 #include <algorithm>
-#include <math.h>
-#include <string.h>
+#include <cmath>
+#include <cstring>
 
 template <class T, class int_type>
 static void
diff --git a/libqpdf/QTC.cc b/libqpdf/QTC.cc
index 8188846..e537a0e 100644
--- a/libqpdf/QTC.cc
+++ b/libqpdf/QTC.cc
@@ -3,7 +3,7 @@
 #include <qpdf/QUtil.hh>
 #include <map>
 #include <set>
-#include <stdio.h>
+#include <cstdio>
 
 static bool
 tc_active(char const* const scope)
diff --git a/libqpdf/QUtil.cc b/libqpdf/QUtil.cc
index 72b2a55..4f9c102 100644
--- a/libqpdf/QUtil.cc
+++ b/libqpdf/QUtil.cc
@@ -9,8 +9,8 @@
 #include <qpdf/QPDFSystemError.hh>
 #include <qpdf/QTC.hh>
 
-#include <ctype.h>
-#include <errno.h>
+#include <cctype>
+#include <cerrno>
 #include <fcntl.h>
 #include <fstream>
 #include <iomanip>
@@ -21,9 +21,9 @@
 #include <set>
 #include <sstream>
 #include <stdexcept>
-#include <stdio.h>
-#include <stdlib.h>
-#include <string.h>
+#include <cstdio>
+#include <cstdlib>
+#include <cstring>
 #ifndef QPDF_NO_WCHAR_T
 # include <cwchar>
 #endif
diff --git a/libqpdf/qpdf/BitStream.hh b/libqpdf/qpdf/BitStream.hh
index 14555c5..b807f56 100644
--- a/libqpdf/qpdf/BitStream.hh
+++ b/libqpdf/qpdf/BitStream.hh
@@ -3,7 +3,7 @@
 #ifndef BITSTREAM_HH
 #define BITSTREAM_HH
 
-#include <stddef.h>
+#include <cstddef>
 
 class BitStream
 {
diff --git a/libqpdf/qpdf/BitWriter.hh b/libqpdf/qpdf/BitWriter.hh
index ca237d4..33fdd8f 100644
--- a/libqpdf/qpdf/BitWriter.hh
+++ b/libqpdf/qpdf/BitWriter.hh
@@ -3,7 +3,7 @@
 #ifndef BITWRITER_HH
 #define BITWRITER_HH
 
-#include <stddef.h>
+#include <cstddef>
 
 class Pipeline;
 
diff --git a/libtests/aes.cc b/libtests/aes.cc
index 3ad491c..4541fff 100644
--- a/libtests/aes.cc
+++ b/libtests/aes.cc
@@ -4,9 +4,9 @@
 #include <qpdf/QUtil.hh>
 
 #include <iostream>
-#include <stdio.h>
-#include <stdlib.h>
-#include <string.h>
+#include <cstdio>
+#include <cstdlib>
+#include <cstring>
 
 static void
 usage()
diff --git a/libtests/ascii85.cc b/libtests/ascii85.cc
index 2acc56b..8d92689 100644
--- a/libtests/ascii85.cc
+++ b/libtests/ascii85.cc
@@ -2,7 +2,7 @@
 
 #include <qpdf/Pl_StdioFile.hh>
 #include <iostream>
-#include <stdlib.h>
+#include <cstdlib>
 
 int
 main()
diff --git a/libtests/bits.cc b/libtests/bits.cc
index 0db956e..e63ebdd 100644
--- a/libtests/bits.cc
+++ b/libtests/bits.cc
@@ -4,7 +4,7 @@
 #include <qpdf/QIntC.hh>
 #include <qpdf/QUtil.hh>
 #include <iostream>
-#include <stdlib.h>
+#include <cstdlib>
 
 // See comments in bits_functions.hh
 #define BITS_TESTING 1
diff --git a/libtests/buffer.cc b/libtests/buffer.cc
index f372e7b..66eaa71 100644
--- a/libtests/buffer.cc
+++ b/libtests/buffer.cc
@@ -7,7 +7,7 @@
 #include <cstring>
 #include <iostream>
 #include <stdexcept>
-#include <stdlib.h>
+#include <cstdlib>
 
 static unsigned char*
 uc(char const* s)
diff --git a/libtests/closed_file_input_source.cc b/libtests/closed_file_input_source.cc
index 23b1515..183658a 100644
--- a/libtests/closed_file_input_source.cc
+++ b/libtests/closed_file_input_source.cc
@@ -2,7 +2,7 @@
 #include <qpdf/FileInputSource.hh>
 
 #include <iostream>
-#include <stdio.h>
+#include <cstdio>
 
 void
 check(std::string const& what, bool result)
diff --git a/libtests/dct_compress.cc b/libtests/dct_compress.cc
index ad8710b..2f12aea 100644
--- a/libtests/dct_compress.cc
+++ b/libtests/dct_compress.cc
@@ -3,9 +3,9 @@
 #include <qpdf/QUtil.hh>
 
 #include <iostream>
-#include <stdio.h>
-#include <stdlib.h>
-#include <string.h>
+#include <cstdio>
+#include <cstdlib>
+#include <cstring>
 
 static void
 usage()
diff --git a/libtests/dct_uncompress.cc b/libtests/dct_uncompress.cc
index 5e1e9a3..6606e4a 100644
--- a/libtests/dct_uncompress.cc
+++ b/libtests/dct_uncompress.cc
@@ -3,8 +3,8 @@
 #include <qpdf/QUtil.hh>
 
 #include <iostream>
-#include <stdio.h>
-#include <stdlib.h>
+#include <cstdio>
+#include <cstdlib>
 
 int
 main(int argc, char* argv[])
diff --git a/libtests/flate.cc b/libtests/flate.cc
index 1170841..93c41f8 100644
--- a/libtests/flate.cc
+++ b/libtests/flate.cc
@@ -5,7 +5,7 @@
 #include <qpdf/QUtil.hh>
 
 #include <iostream>
-#include <stdlib.h>
+#include <cstdlib>
 
 void
 run(char const* filename)
diff --git a/libtests/hex.cc b/libtests/hex.cc
index 9e70820..d239d20 100644
--- a/libtests/hex.cc
+++ b/libtests/hex.cc
@@ -2,7 +2,7 @@
 
 #include <qpdf/Pl_StdioFile.hh>
 #include <iostream>
-#include <stdlib.h>
+#include <cstdlib>
 
 int
 main()
diff --git a/libtests/lzw.cc b/libtests/lzw.cc
index 788d3df..412ce4c 100644
--- a/libtests/lzw.cc
+++ b/libtests/lzw.cc
@@ -3,8 +3,8 @@
 #include <qpdf/Pl_StdioFile.hh>
 #include <qpdf/QUtil.hh>
 #include <iostream>
-#include <stdlib.h>
-#include <string.h>
+#include <cstdlib>
+#include <cstring>
 
 int
 main(int argc, char* argv[])
diff --git a/libtests/md5.cc b/libtests/md5.cc
index 0fe4205..27aaad5 100644
--- a/libtests/md5.cc
+++ b/libtests/md5.cc
@@ -3,7 +3,7 @@
 #include <qpdf/Pl_MD5.hh>
 #include <qpdf/QUtil.hh>
 #include <iostream>
-#include <stdio.h>
+#include <cstdio>
 
 static void
 test_string(char const* str)
diff --git a/libtests/predictors.cc b/libtests/predictors.cc
index f0bde79..fd1cc2a 100644
--- a/libtests/predictors.cc
+++ b/libtests/predictors.cc
@@ -7,8 +7,8 @@
 #include <qpdf/QUtil.hh>
 
 #include <iostream>
-#include <stdlib.h>
-#include <string.h>
+#include <cstdlib>
+#include <cstring>
 
 void
 run(char const* filename,
diff --git a/libtests/qintc.cc b/libtests/qintc.cc
index f6c15f0..0cf3924 100644
--- a/libtests/qintc.cc
+++ b/libtests/qintc.cc
@@ -1,7 +1,7 @@
 #include <qpdf/assert_test.h>
 
 #include <qpdf/QIntC.hh>
-#include <stdint.h>
+#include <cstdint>
 
 #define try_convert(exp_pass, fn, i) \
     try_convert_real(#fn "(" #i ")", exp_pass, fn, i)
diff --git a/libtests/qutil.cc b/libtests/qutil.cc
index b9012db..a6f1282 100644
--- a/libtests/qutil.cc
+++ b/libtests/qutil.cc
@@ -5,9 +5,9 @@
 #include <qpdf/QUtil.hh>
 #include <fstream>
 #include <iostream>
-#include <limits.h>
-#include <stdio.h>
-#include <string.h>
+#include <climits>
+#include <cstdio>
+#include <cstring>
 
 #ifdef _WIN32
 # include <io.h>
diff --git a/libtests/rc4.cc b/libtests/rc4.cc
index a6a1328..874c11f 100644
--- a/libtests/rc4.cc
+++ b/libtests/rc4.cc
@@ -6,9 +6,9 @@
 #include <qpdf/QUtil.hh>
 
 #include <iostream>
-#include <stdio.h>
-#include <stdlib.h>
-#include <string.h>
+#include <cstdio>
+#include <cstdlib>
+#include <cstring>
 
 static void
 other_tests()
diff --git a/libtests/runlength.cc b/libtests/runlength.cc
index 456e33a..260ce5c 100644
--- a/libtests/runlength.cc
+++ b/libtests/runlength.cc
@@ -3,9 +3,9 @@
 #include <qpdf/QUtil.hh>
 
 #include <iostream>
-#include <stdio.h>
-#include <stdlib.h>
-#include <string.h>
+#include <cstdio>
+#include <cstdlib>
+#include <cstring>
 
 int
 main(int argc, char* argv[])
diff --git a/libtests/sha2.cc b/libtests/sha2.cc
index 46ccd5c..4be8956 100644
--- a/libtests/sha2.cc
+++ b/libtests/sha2.cc
@@ -1,7 +1,7 @@
 #include <qpdf/Pl_SHA2.hh>
 #include <qpdf/QUtil.hh>
 #include <iostream>
-#include <string.h>
+#include <cstring>
 
 static void
 test(
diff --git a/qpdf/pdf_from_scratch.cc b/qpdf/pdf_from_scratch.cc
index 4e1c655..1b17296 100644
--- a/qpdf/pdf_from_scratch.cc
+++ b/qpdf/pdf_from_scratch.cc
@@ -5,9 +5,9 @@
 #include <qpdf/QPDFWriter.hh>
 #include <qpdf/QUtil.hh>
 #include <iostream>
-#include <stdio.h>
-#include <stdlib.h>
-#include <string.h>
+#include <cstdio>
+#include <cstdlib>
+#include <cstring>
 
 static char const* whoami = 0;
 
diff --git a/qpdf/test_driver.cc b/qpdf/test_driver.cc
index 39631d2..673c6b5 100644
--- a/qpdf/test_driver.cc
+++ b/qpdf/test_driver.cc
@@ -27,12 +27,12 @@
 #include <qpdf/QTC.hh>
 #include <qpdf/QUtil.hh>
 #include <iostream>
-#include <limits.h>
+#include <climits>
 #include <map>
 #include <sstream>
-#include <stdio.h>
-#include <stdlib.h>
-#include <string.h>
+#include <cstdio>
+#include <cstdlib>
+#include <cstring>
 
 #define QPDF_OBJECT_NOWARN
 #include <qpdf/QPDFObject.hh>
diff --git a/qpdf/test_large_file.cc b/qpdf/test_large_file.cc
index e8bea10..b30967c 100644
--- a/qpdf/test_large_file.cc
+++ b/qpdf/test_large_file.cc
@@ -13,8 +13,8 @@
 #include <qpdf/QPDFWriter.hh>
 #include <qpdf/QUtil.hh>
 #include <iostream>
-#include <stdlib.h>
-#include <string.h>
+#include <cstdlib>
+#include <cstring>
 
 // Run "test_large_file write small a.pdf" to get a PDF file that you
 // can look at in a reader.
diff --git a/qpdf/test_pdf_doc_encoding.cc b/qpdf/test_pdf_doc_encoding.cc
index 5c67f59..cd2e9b4 100644
--- a/qpdf/test_pdf_doc_encoding.cc
+++ b/qpdf/test_pdf_doc_encoding.cc
@@ -1,8 +1,8 @@
 #include <qpdf/QPDFObjectHandle.hh>
 #include <qpdf/QUtil.hh>
 #include <iostream>
-#include <stdlib.h>
-#include <string.h>
+#include <cstdlib>
+#include <cstring>
 
 static char const* whoami = 0;
 
diff --git a/qpdf/test_pdf_unicode.cc b/qpdf/test_pdf_unicode.cc
index 38df6da..b28edea 100644
--- a/qpdf/test_pdf_unicode.cc
+++ b/qpdf/test_pdf_unicode.cc
@@ -1,8 +1,8 @@
 #include <qpdf/QPDFObjectHandle.hh>
 #include <qpdf/QUtil.hh>
 #include <iostream>
-#include <stdlib.h>
-#include <string.h>
+#include <cstdlib>
+#include <cstring>
 
 static char const* whoami = 0;
 
diff --git a/qpdf/test_tokenizer.cc b/qpdf/test_tokenizer.cc
index 83d3e1c..8a58fc8 100644
--- a/qpdf/test_tokenizer.cc
+++ b/qpdf/test_tokenizer.cc
@@ -7,9 +7,9 @@
 #include <qpdf/QPDFTokenizer.hh>
 #include <qpdf/QUtil.hh>
 #include <iostream>
-#include <stdio.h>
-#include <stdlib.h>
-#include <string.h>
+#include <cstdio>
+#include <cstdlib>
+#include <cstring>
 
 static char const* whoami = 0;
 
diff --git a/qpdf/test_unicode_filenames.cc b/qpdf/test_unicode_filenames.cc
index 3d9e803..b2fd50f 100644
--- a/qpdf/test_unicode_filenames.cc
+++ b/qpdf/test_unicode_filenames.cc
@@ -6,8 +6,8 @@
 #endif
 
 #include <iostream>
-#include <stdio.h>
-#include <stdlib.h>
+#include <cstdio>
+#include <cstdlib>
 
 static void
 do_copy(FILE* in, FILE* out)
diff --git a/zlib-flate/zlib-flate.cc b/zlib-flate/zlib-flate.cc
index f7d0c80..8f0f087 100644
--- a/zlib-flate/zlib-flate.cc
+++ b/zlib-flate/zlib-flate.cc
@@ -5,9 +5,9 @@
 
 #include <fcntl.h>
 #include <iostream>
-#include <stdio.h>
-#include <stdlib.h>
-#include <string.h>
+#include <cstdio>
+#include <cstdlib>
+#include <cstring>
 
 static char const* whoami = 0;