在mingw-w64 gcc 7.1中，如何在没有警告的情况下printf size_t? [英] How to printf a size_t without warning in mingw-w64 gcc 7.1?

问题描述

我正在使用nuwen.net上准备的minGW的mingw-w64(x64)分支.这是来自7.1版本的gcc:

I am using the mingw-w64 (x64) fork of minGW as prepared on nuwen.net. This is from the 7.1 version of gcc :

gcc --version
gcc (GCC) 7.1.0

我正在编译该程序:

#include <stdio.h>

int main(void)
{
    size_t a = 100;
    printf("a=%lu\n",a);
    printf("a=%llu\n",a);
    printf("a=%zu\n",a);
    printf("a=%I64u\n",a);
}

带有警告和c11标准的

with warnings and c11 standard:

gcc -Wall -Wextra -Wpedantic -std=c11 test_size_t.c

我收到这些警告:

   test_size_t.c: In function 'main':
    test_size_t.c:6:14: warning: format '%lu' expects argument of type 'long unsigned int', but argument 2 has type 'size_t {aka long long unsigned int}' [-Wformat=]
      printf("a=%lu\n",a);
                ~~^
                %I64u
    test_size_t.c:6:14: warning: format '%lu' expects argument of type 'long unsigned int', but argument 2 has type 'size_t {aka long long unsigned int}' [-Wformat=]
      printf("a=%lu\n",a);
                ~~^
                %I64u
    test_size_t.c:7:14: warning: unknown conversion type character 'l' in format [-Wformat=]
      printf("a=%llu\n",a);
                  ^
    test_size_t.c:7:9: warning: too many arguments for format [-Wformat-extra-args]
      printf("a=%llu\n",a);
             ^~~~~~~~~~
    test_size_t.c:7:14: warning: unknown conversion type character 'l' in format [-Wformat=]
      printf("a=%llu\n",a);
                  ^
    test_size_t.c:7:9: warning: too many arguments for format [-Wformat-extra-args]
      printf("a=%llu\n",a);
             ^~~~~~~~~~
    test_size_t.c:8:13: warning: unknown conversion type character 'z' in format [-Wformat=]
      printf("a=%zu\n",a);
                 ^
    test_size_t.c:8:9: warning: too many arguments for format [-Wformat-extra-args]
      printf("a=%zu\n",a);
             ^~~~~~~~~
    test_size_t.c:8:13: warning: unknown conversion type character 'z' in format [-Wformat=]
      printf("a=%zu\n",a);
                 ^
    test_size_t.c:8:9: warning: too many arguments for format [-Wformat-extra-args]
      printf("a=%zu\n",a);
             ^~~~~~~~~
    test_size_t.c:9:9: warning: ISO C does not support the 'I64' ms_printf length modifier [-Wformat=]
      printf("a=%I64u\n",a);
         ^~~~~~~~~~~
    test_size_t.c:9:9: warning: ISO C does not support the 'I64' ms_printf length modifier [-Wformat=]

我想在没有警告的情况下打印size_t，但是在这种情况下我不知道正确的格式说明符.

I would like to printf a size_t without warning but don't know the correct format specifier in this situation.

推荐答案

问题不是编译器，而是C库. MinGW使用Microsoft的"Visual C运行时"(msvcrt)，它仅符合 c89 ，它不支持z格式说明符.

The problem is not the compiler but the C library. MinGW uses Microsoft's "Visual C Runtime" (msvcrt) which only conforms to c89 and it doesn't support the z format specifier.

这是使用MinGW时可以安全打印size_t的方法:

Here's what you can do to safely print a size_t when using MinGW:

#include <inttypes.h>
#include <stdio.h>

#ifdef _WIN32
#  ifdef _WIN64
#    define PRI_SIZET PRIu64
#  else
#    define PRI_SIZET PRIu32
#  endif
#else
#  define PRI_SIZET "zu"
#endif

int main(void)
{
    size_t mySize = 24;

    printf("%" PRI_SIZET "\n", mySize);
}

在win64上，此代码会警告您，因为PRIu64会扩展为特定于msvcrt的I64u格式说明符.但是您可以使用GCC标志-Wno-pedantic-ms-format使该警告静音.

On win64, you would get a warning with this code, because PRIu64 expands to the msvcrt-specific I64u format specifier. But you can silence this warning with the GCC flag -Wno-pedantic-ms-format.

请注意，对于long long(在32位和64位窗口上都使用PRIu64)，您也需要类似的技巧，因为msvcrt也不知道ll.

Note that you need a similar trick for long long (here using PRIu64 on both 32bit and 64bit windows) because msvcrt doesn't know ll either.

edit :正如@ M.M在评论中指出的那样，您可以将MinGW提供的支持#define __USE_MINGW_ANSI_STDIO 1的替代stdio函数链接到#define __USE_MINGW_ANSI_STDIO 1.如果我能解决msvcrt的特殊之处，我不希望链接多余的代码，但这当然是一个趣味问题.

edit: as pointed out by @M.M in a comment, you can instead link MinGW-provided alternative stdio functions that support C11 with #define __USE_MINGW_ANSI_STDIO 1. I prefer not to link extra code if I can get around the peculiarities of msvcrt, but that's of course a matter of taste.

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