我得到了下面的代码:我不明白为什么我得到这个错误Valgrind的
/* main.c */
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
int main(){
int i;
char *msg = "This is a simple and small message";
int len = strlen (msg);
char *new_msg = (char *) malloc (len);
for (i = 0; i < len; i++)
new_msg[i] = 'A';
printf ("%s\n", new_msg);
free (new_msg);
return 0;
}
我编译它,然后使用Valgrind的使用下面的命令运行它:
valgrind --leak-check=full --show-reachable=yes ./main
我得到了这个输出:
==8286== Memcheck, a memory error detector
==8286== Copyright (C) 2002-2013, and GNU GPL'd, by Julian Seward et al.
==8286== Using Valgrind-3.10.1 and LibVEX; rerun with -h for copyright info
==8286== Command: ./main
==8286==
==8286== Invalid read of size 1
==8286== at 0x4C2C1B4: strlen (vg_replace_strmem.c:412)
==8286== by 0x4EA09FB: puts (ioputs.c:36)
==8286== by 0x400636: main (main.c:12)
==8286== Address 0x51de062 is 0 bytes after a block of size 34 alloc'd
==8286== at 0x4C28C20: malloc (vg_replace_malloc.c:296)
==8286== by 0x400601: main (main.c:9)
==8286==
AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
==8286==
==8286== HEAP SUMMARY:
==8286== in use at exit: 0 bytes in 0 blocks
==8286== total heap usage: 1 allocs, 1 frees, 34 bytes allocated
==8286==
==8286== All heap blocks were freed -- no leaks are possible
==8286==
==8286== For counts of detected and suppressed errors, rerun with: -v
==8286== ERROR SUMMARY: 1 errors from 1 contexts (suppressed: 0 from 0)
我看到所有分配的内存被释放,但我仍然得到一个我不明白的错误。
欣赏帮助。
首先,感谢您的解释。现在它可以工作。其次,我看到你删除了malloc的转换。这是为什么?我在没有演员的情况下运行它,仍然得到相同的输出(即使在valgrind上)。有什么区别吗? –
@mikmik [这里是关于强制'malloc'结果的一个很好的问答](http://stackoverflow.com/q/605845/335858)。不投射背后的想法是,你已经指定了类型,所以你再次重复同一段代码。演员也可以隐藏细微的错误。 – dasblinkenlight
O.K.谢谢! –