在Mac OS X Valgrind的误差printf的双 [英] Valgrind Errors on Mac OS X for printf a double
问题描述
目前我正在学习C与真棒学习codethehardway系列的时刻。
我遇到了以下内容：
At the moment I am learning C with the awesome learncodethehardway series. I encountered the following:
我编译如下code，一切看起来完全正常对我说：
I compile the following code and everything looks totally fine to me:
#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;
}
它的工作原理也正常。
It works also correctly.
当我现在运行Valgrind的（3.11.0; 应OS X埃尔卡皮坦更新）我得到以下信息：
When I run now Valgrind (3.11.0; should be updated for OS X El Capitan) I get following messages:
==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)
我不明白这一点。有什么错我的行：10 的是不是
THX了很多。
推荐答案
不幸的是，的printf 使用的库，总是不以理想的方式。 Valgrind的会发现所有的错误 - 不仅是你做的那些，但在OSX标准C库方面取得的每一个错误，例如
Unfortunately, the libraries that printf uses, do not always behave in an ideal way. Valgrind will notice all errors - not only the ones you made, but every error made in the standard C library implementation on OSX, for instance.
其中的一些错误可能是实际的错误（这是pretty少见），其他人可能有点快捷键库的开发了，这可能不是看起来完全正确的Valgrind的。一个这样的事情是依靠的操作系统的清除，并释放所有遗留当程序退出记忆 - 当一个迂腐的世界，程序应该退出之前释放所有的内存。然而，这种停止
Some of those "errors" may be actual bugs (which is pretty rare), others are likely little shortcuts the library developers took, which may not look completely correct to Valgrind. One such thing is to rely on the operating system to clear and free all left over memory when a program exits - when in a pedantic world, the program should free all of its memory before exit. However, this stopped being strictly necessary somewhere around the days of DOS and AmigaOS.
我不是说这一定是你在该错误看到，但你必须牢记的是什么Valgrind的说。
I am not saying this is necessarily what you are seeing in that error, but that you need to be mindful of what Valgrind says.
要在实践中使用Valgrind的，你可能需要一个SUP pression文件，删除相关的系统库的错误消息。这里是一个略微最近（2015年1月）的有关此问题的博客帖子里面传来究竟在OSX学习C辛苦的感觉。
To use Valgrind in practice, you may want a suppression file, which removes error messages related to system libraries. Here is a somewhat recent (January 2015) blog post about this issue which came about exactly because of "learning C the hard way" on OSX.
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