Compiling this C or C++ file:
#define __STDC_FORMAT_MACROS 1
#define __STDC_FORMAT_MACROS 1
produces these warnings:
foo.c:2:1: warning: "__STDC_FORMAT_MACROS" redefined
foo.c:1:1: warning: this is the location of the previous definition
This is because of these lines in libcpp/macro.c:
if (! ustrncmp (NODE_NAME (node), DSC ("__STDC_")))
node->flags |= NODE_WARN;
The idea behind these lines is sound: the compiler defines macros whose name
begins with "__STDC_". The user should not redefine them.
However, __STDC_FORMAT_MACROS is an exception here. This macro is not defined
by the compiler. It is intended to be defined by the user when compiling a C++
file to direct the <stdint.h> header file to define macros PRId32 and friends.
See footnote 182 in section 7.8.1 in C99.
If the user defines the macro in a .h file, as is permitted, then including
that some .h file twice, if it does not have an include guard, will give an
inappropriate warning. In particular this can happen with an autoconf-style
config.h file, as autoconf does not generate include guards for such files.
I expect that the right fix is to specifically exclude __STDC_FORMAT_MACROS
from this warning. Or perhaps another approach would be to specially mark the
macros defined in cpp_init_builtins.
--
Summary: Don't warn about redefinitions of __STDC_FORMAT_MACROS
Product: gcc
Version: 4.3.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: preprocessor
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: ian at airs dot com
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32868
