Calloc 导致分段错误
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==
Here is my code:
#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;
}
The intent is to assing 2 digit number to a (char *).
when I run the code, I get segmentation fault. Outout from valgrind is-
==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==
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您只为 2 个字符分配空间，然后放置字符串“10\0”，该字符串需要另一个字符来保存 null/0 终止字符。因此，您需要为这个特定示例分配 3 个字符才能工作。
阅读C 字符串了解完整详细信息。
You allocate space for just 2 chars and then put the string '10\0' which needs another char to hold the null/0 terminating character. So you need to allocate 3 chars for this particular example to work.
Read up C Strings for full details.
您分配了 2 个字节，但字符串大小为 3：
'1'、'0'、'\0'（空终止符），在这种情况下结果未定义，因为您损坏了堆
此外，当您分配内存时，不要最后忘记拨打免费电话。
You allocate 2 bytes, but the string size is 3:
'1', '0', '\0' (null terminator) the result is undefined in this case since you corrupt the heap
Also, when you allocate memory, don't forget to call free at the end.
您需要为空终止字符串的空字符分配空间。总共 3 个字符。
另外
printf(s);应该是：printf("%s", s);You need to allocate room for the null character of a null terminated string. That's 3 characters total.
Also
printf(s);should be:printf("%s", s);对于这段特定的代码，字符串“10”需要 3 个字节，即 '1'、'0' 和 '\0' 。所以需要分配3个字节的内存。
For this particular piece of code the string "10" requires 3 bytes, which are '1', '0', and '\0' . So you need 3 bytes of memory to be allocated.