[PATCH] D24903: [libcxx] [include] Declare __STDC_*_MACROS for C++11 compat in old libc

Michał Górny via cfe-commits cfe-commits at lists.llvm.org
Sun Sep 25 13:42:54 PDT 2016

mgorny created this revision.
mgorny added a reviewer: EricWF.
mgorny added a subscriber: cfe-commits.

Declare __STDC_FORMAT_MACROS, __STDC_LIMIT_MACROS and __STDC_CONSTANT_MACROS before including real inttypes.h/stdint.h when the wrapper-header is included in C++11, in order to enable the necessary macros in C99-compliant libc.

The C99 standard defined that the format macros in inttypes.h should be defined by the C++ implementations only when __STDC_FORMAT_MACROS is defined, and the limit and constant macros in stdint.h should be defined only when __STDC_LIMIT_MACROS and __STDC_CONSTANT_MACROS are defined appropriately. Following this specification, multiple old versions of glibc up to 2.17 do not define those macros by default for C++, rendering the libc++ headers non-compliant to the C++11 standard.

In order to achieve the necessary compliance, __STDC_FORMAT_MACROS is defined in wrapped inttypes.h just before including the system inttypes.h, when C++11 or newer is used. Both __STDC_LIMIT_MACROS and __STDC_CONSTANT_MACROS are defined in newly-wrapped stdint.h. This fixes the C++11 compliance while preserving the current behavior for C++03.



Index: include/stdint.h
--- /dev/null
+++ include/stdint.h
@@ -0,0 +1,33 @@
+// -*- C++ -*-
+//===---------------------------- stdint.h --------------------------------===//
+//                     The LLVM Compiler Infrastructure
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+#include <__config>
+#pragma GCC system_header
+/* C99 stdlib (e.g. glibc < 2.18) does not provide macros needed
+   are defined
+#if __cplusplus >= 201103L && !defined(__STDC_LIMIT_MACROS)
+#if __cplusplus >= 201103L && !defined(__STDC_CONSTANT_MACROS)
+#include_next <stdint.h>
+#endif  // _LIBCPP_STDINT_H
Index: include/inttypes.h
--- include/inttypes.h
+++ include/inttypes.h
@@ -237,6 +237,13 @@
 #pragma GCC system_header
+/* C99 stdlib (e.g. glibc < 2.18) does not provide format macros needed
+   for C++11 unless __STDC_FORMAT_MACROS is defined
+#if __cplusplus >= 201103L && !defined(__STDC_FORMAT_MACROS)
 #include_next <inttypes.h>
 #ifdef __cplusplus

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