为什么会出现内存泄漏？答案

【问题标题】：Why do I get memory leak?为什么会出现内存泄漏？
【发布时间】：2018-09-17 00:13:53
【问题描述】：

考虑以下代码：＃包括 #包括

int main () {
   char *str;

   /* Initial memory allocation */
   str = (char *) malloc(15);
   strcpy(str, "tutorialspoint");
   printf("String = %s,  Address = %u\n", str, str);
   str = NULL;

   free(str);

   return(0);
}

为什么上面的程序会导致内存泄漏？我该如何避免这种情况？

认为“str = NULL;”中发生了错误。为什么？

valgrind 日志：

==4143== Memcheck, a memory error detector
==4143== Copyright (C) 2002-2017, and GNU GPL'd, by Julian Seward et al.
==4143== Using Valgrind-3.13.0 and LibVEX; rerun with -h for copyright info
==4143== Command: ./a.out
==4143== 
String = tutorialspoint,  Address = 86097984
==4143== 
==4143== HEAP SUMMARY:
==4143==     in use at exit: 15 bytes in 1 blocks
==4143==   total heap usage: 2 allocs, 1 frees, 1,039 bytes allocated
==4143== 
==4143== 15 bytes in 1 blocks are definitely lost in loss record 1 of 1
==4143==    at 0x4C2FB0F: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==4143==    by 0x1086EB: main (in /home/stack/a.out)
==4143== 
==4143== LEAK SUMMARY:
==4143==    definitely lost: 15 bytes in 1 blocks
==4143==    indirectly lost: 0 bytes in 0 blocks
==4143==      possibly lost: 0 bytes in 0 blocks
==4143==    still reachable: 0 bytes in 0 blocks
==4143==         suppressed: 0 bytes in 0 blocks
==4143== 
==4143== For counts of detected and suppressed errors, rerun with: -v
==4143== ERROR SUMMARY: 1 errors from 1 contexts (suppressed: 0 from 0)

【问题讨论】：

你为什么有str = NULL; 行呢？你觉得它有什么作用？

标签： memory memory-leaks null

【解决方案1】：

free(str);释放str指向的空间，其中str是malloc获得的空间。由于str = NULL; 行发生在free 之前，free 正试图释放位置0 的内存位置。根据 C 标准中的定义，这没有任何作用。通常在删除后设置指向0 的指针，这样如果不小心再次尝试删除它，什么也不会发生。

要修复您的代码，您只需交换行 str = NULL; 和 free(str);

【讨论】：