我的任务是编写一个使用动态内存的函数,它将获取一个字符串 s
并取出该字符串的每个第二个元素,然后返回一个包含这些元素的新字符串。到目前为止我的代码是:
#include <stdlib.h>
#include <string.h>
#include <stdio.h>
char* skipping(const char* s)
{
int inc = 0; //new list incrementer
int len = strlen(s);
char* new_s = malloc(len + 1);
for (int i = 0; i < len - 1; i+=2) {
new_s[inc] = s[i];
inc++;
}
return new_s;
}
int main(void)
{
char* s = skipping("0123456789");
printf("%s\n", s);
free(s);
return 0;
}
这有效,但是当我使用 Valgrind 运行它时,我被告知我有一个错误,该错误来自使用 strlen
,但我似乎无法修复它。任何帮助都会很棒!
错误信息:(在 valgrind 中)
==4596==
==4596== Conditional jump or move depends on uninitialised value(s)
==4596== at 0x4C32D08: strlen (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==4596== by 0x4EBC9D1: puts (ioputs.c:35)
==4596== by 0x1087B4: main (in /home/ryan/ENCE260/lab6)
==4596==
02468 //this is the expected output
==4596==
==4596== HEAP SUMMARY:
==4596== in use at exit: 0 bytes in 0 blocks
==4596== total heap usage: 2 allocs, 2 frees, 1,035 bytes allocated
==4596==
==4596== All heap blocks were freed -- no leaks are possible
==4596==
==4596== ERROR SUMMARY: 1 errors from 1 contexts (suppressed: 0 from 0)
最佳答案
为什么 Valgrind 报告这个错误?
来自 Valgrind online manual在 use of uninitialised or unaddressable values in system calls 上:
Sources of uninitialised data tend to be:
- Local variables in procedures which have not been initialised.
- The contents of heap blocks (allocated with malloc, new, or a similar function) before you (or a constructor) write something there.
如果出现以下情况,Valgrind 会报错:
the program has written uninitialised junk from the heap block to the standard output.
因为您在 printf
中使用了 s
而没有以 null 终止它,所以它导致了错误。
关于c - 使用动态内存将 char 数组中的每个第二个元素放入另一个,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/52069899/