Calloc 导致分段错误答案

【问题标题】：Calloc causing segmentation faultCalloc 导致分段错误
【发布时间】：2011-07-23 03:19:10
【问题描述】：

这是我的代码：

#include <stdio.h>
#include <stdlib.h>

int main(){
int n=10;
char *s= calloc(2,sizeof(char));
sprintf(s,"%d",n);
printf(s);
return 0;
}

目的是将 2 位数字分配给 (char *)。当我运行代码时，出现分段错误。 valgrind 的输出是-

==18540== Command: ./test
==18540== 
==18540== Conditional jump or move depends on uninitialised value(s)
==18540==    at 0x366C06F397: _IO_str_init_static_internal (in /lib64/libc-2.5.so)
==18540==    by 0x366C063C8A: vsprintf (in /lib64/libc-2.5.so)
==18540==    by 0x366C04D677: sprintf (in /lib64/libc-2.5.so)
==18540==    by 0x4004FC: main (test.c:8)
==18540== 
==18540== Conditional jump or move depends on uninitialised value(s)
==18540==    at 0x366C06E37B: _IO_default_xsputn (in /lib64/libc-2.5.so)
==18540==    by 0x366C043D38: vfprintf (in /lib64/libc-2.5.so)
==18540==    by 0x366C063C98: vsprintf (in /lib64/libc-2.5.so)
==18540==    by 0x366C04D677: sprintf (in /lib64/libc-2.5.so)
==18540==    by 0x4004FC: main (test.c:8)
==18540== 
==18540== Conditional jump or move depends on uninitialised value(s)
==18540==    at 0x366C06F20A: _IO_str_overflow (in /lib64/libc-2.5.so)
==18540==    by 0x366C06E3E3: _IO_default_xsputn (in /lib64/libc-2.5.so)
==18540==    by 0x366C043D38: vfprintf (in /lib64/libc-2.5.so)
==18540==    by 0x366C063C98: vsprintf (in /lib64/libc-2.5.so)
==18540==    by 0x366C04D677: sprintf (in /lib64/libc-2.5.so)
==18540==    by 0x4004FC: main (test.c:8)
==18540== 
==18540== Use of uninitialised value of size 8
==18540==    at 0x366C06F241: _IO_str_overflow (in /lib64/libc-2.5.so)
==18540==    by 0x366C06E3E3: _IO_default_xsputn (in /lib64/libc-2.5.so)
==18540==    by 0x366C043D38: vfprintf (in /lib64/libc-2.5.so)
==18540==    by 0x366C063C98: vsprintf (in /lib64/libc-2.5.so)
==18540==    by 0x366C04D677: sprintf (in /lib64/libc-2.5.so)
==18540==    by 0x4004FC: main (test.c:8)
==18540== 
==18540== Invalid write of size 1
==18540==    at 0x366C06F241: _IO_str_overflow (in /lib64/libc-2.5.so)
==18540==    by 0x366C06E3E3: _IO_default_xsputn (in /lib64/libc-2.5.so)
==18540==    by 0x366C043D38: vfprintf (in /lib64/libc-2.5.so)
==18540==    by 0x366C063C98: vsprintf (in /lib64/libc-2.5.so)
==18540==    by 0x366C04D677: sprintf (in /lib64/libc-2.5.so)
==18540==    by 0x4004FC: main (test.c:8)
==18540==  Address 0x0 is not stack'd, malloc'd or (recently) free'd
==18540==

【问题讨论】：

标签： c segmentation-fault calloc dynamic-allocation

【解决方案1】：

您只为 2 个字符分配空间，然后放置字符串 '10\0'，它需要另一个字符来保存空 / 0 终止字符。因此，您需要为这个特定示例分配 3 个字符才能正常工作。

阅读C Strings 了解完整详情。

【讨论】：

【解决方案2】：

你分配了 2 个字节，但字符串大小是 3：

'1', '0', '\0' (null 终止符) 在这种情况下结果是不确定的，因为你破坏了堆

另外，在分配内存的时候，别忘了最后调用free。

【讨论】：

另一种解决方案（仅适用于这种情况）是sprintf(s, "%X", n); ;-P

【解决方案3】：

您需要为空终止字符串的空字符分配空间。总共 3 个字符。

printf(s); 也应该是：printf("%s", s);

【讨论】：

【解决方案4】：

对于这段特定的代码，字符串 "10" 需要 3 个字节，即 '1'、'0' 和 '\0' 。所以你需要分配 3 个字节的内存。

【讨论】：