Mac OS X for printf a double 上的 Valgrind 错误

Question

目前正在跟牛逼learncodethehardway series学C。我遇到了以下情况：

我编译了以下代码，一切看起来都很好：

#include <stdio.h>

int main(int argc, char *argv[]) {

    int bugs = 100;
    double bug_rate = 1.2;

    printf("You have %d bugs a the imaginary rate of %f!\n", bugs, bug_rate);

    return 0;
}

它也能正常工作。

当我运行现在使用 Valgrind (3.11.0; should be updated for OS X El Capitan) 时，我收到以下消息：

==18896== Memcheck, a memory error detector
==18896== Copyright (C) 2002-2015, and GNU GPL'd, by Julian Seward et al.
==18896== Using Valgrind-3.11.0 and LibVEX; rerun with -h for copyright info
==18896== Command: ./ex7
==18896==
You have 100 bugs a the imaginary rate of 1.200000!
==18896==
==18896== HEAP SUMMARY:
==18896==     in use at exit: 26,081 bytes in 188 blocks
==18896==   total heap usage: 272 allocs, 84 frees, 32,321 bytes allocated
==18896==
==18896== 148 (80 direct, 68 indirect) bytes in 1 blocks are definitely lost in loss record 42 of 65
==18896==    at 0x100007EA1: malloc (vg_replace_malloc.c:303)
==18896==    by 0x1001C58D6: __Balloc_D2A (in /usr/lib/system/libsystem_c.dylib)
==18896==    by 0x1001C621F: __d2b_D2A (in /usr/lib/system/libsystem_c.dylib)
==18896==    by 0x1001C2877: __dtoa (in /usr/lib/system/libsystem_c.dylib)
==18896==    by 0x1001EB3E6: __vfprintf (in /usr/lib/system/libsystem_c.dylib)
==18896==    by 0x1002146C8: __v2printf (in /usr/lib/system/libsystem_c.dylib)
==18896==    by 0x1001EA389: vfprintf_l (in /usr/lib/system/libsystem_c.dylib)
==18896==    by 0x1001E8223: printf (in /usr/lib/system/libsystem_c.dylib)
==18896==    by 0x100000F32: main (ex7.c:10)
==18896==
==18896== 2,064 bytes in 1 blocks are possibly lost in loss record 59 of 65
==18896==    at 0x10000821C: malloc_zone_malloc (vg_replace_malloc.c:305)
==18896==    by 0x1004F6EFD: _objc_copyClassNamesForImage (in /usr/lib/libobjc.A.dylib)
==18896==    by 0x1004EA182: protocols() (in /usr/lib/libobjc.A.dylib)
==18896==    by 0x1004EA093: readClass(objc_class*, bool, bool) (in /usr/lib/libobjc.A.dylib)
==18896==    by 0x1004E7C13: gc_init (in /usr/lib/libobjc.A.dylib)
==18896==    by 0x1004EF24E: objc_initializeClassPair_internal(objc_class*, char const*, objc_class*, objc_class*) (in /usr/lib/libobjc.A.dylib)
==18896==    by 0x1004FC132: layout_string_create (in /usr/lib/libobjc.A.dylib)
==18896==    by 0x1004EA83C: realizeClass(objc_class*) (in /usr/lib/libobjc.A.dylib)
==18896==    by 0x1004EA300: copySwiftV1MangledName(char const*, bool) (in /usr/lib/libobjc.A.dylib)
==18896==    by 0x1004EA2E9: copySwiftV1MangledName(char const*, bool) (in /usr/lib/libobjc.A.dylib)
==18896==    by 0x1004EA2E9: copySwiftV1MangledName(char const*, bool) (in /usr/lib/libobjc.A.dylib)
==18896==    by 0x1004EA2E9: copySwiftV1MangledName(char const*, bool) (in /usr/lib/libobjc.A.dylib)
==18896==
==18896== LEAK SUMMARY:
==18896==    definitely lost: 80 bytes in 1 blocks
==18896==    indirectly lost: 68 bytes in 2 blocks
==18896==      possibly lost: 2,064 bytes in 1 blocks
==18896==    still reachable: 0 bytes in 0 blocks
==18896==         suppressed: 23,869 bytes in 184 blocks
==18896==
==18896== For counts of detected and suppressed errors, rerun with: -v
==18896== ERROR SUMMARY: 2 errors from 2 contexts (suppressed: 18 from 18)

我不明白。我的 line:10 没问题吧？

非常感谢。

Answer 1

不幸的是，printf 使用的库并不总是以理想的方式运行。 Valgrind 会注意到所有错误 - 不仅是您犯的错误，还有在 OSX 上的标准 C 库实现中犯的每个错误。例如。

其中一些 "errors" 可能是真正的错误（这种情况很少见），其他的可能是库开发人员采取的小捷径，这对 Valgrind 来说可能看起来并不完全正确。其中之一是依赖 操作系统 在程序退出时清除和释放所有剩余内存 - 在迂腐的世界中，程序应该在退出前释放所有内存。但是，在 DOS and AmigaOS.

前后的某个地方，这不再是绝对必要的了

我并不是说这一定是您在该错误中看到的内容，而是您需要注意 Valgrind 所说的内容。

要在实践中使用 Valgrind，您可能需要一个抑制文件，它可以删除与系统库相关的错误消息。这是最近的（2015 年 1 月）blog post about this issue，正是因为 "learning C the hard way" 在 OSX.

Mac OS X for printf a double 上的 Valgrind 错误

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