#include <stdio.h>
#include <stdlib.h>
void *g_p1;
void *g_p2;
int ** fun1(void)
{
//内存分配指针付给了局部变量, 函数结束而不释放,为肯定丢失.
//把函数尾部语句return p; 改为return 0;更能说明这个问题.
int **p=(int **)malloc(16);
g_p1=malloc(20); //付给了全局变量, 内存可以访问
g_p2=malloc(30);
g_p2++; //付给了全局变量, 内存可以访问,但是指针被移动过,为可能丢失
p[1]=(int *)malloc(40); //如果p丢失了,则p[1]为间接丢失.
return p;
}
int main(int argc, char *argv[])
{
int **p=fun1();
// free(g_p1); //如果不free, 将会有 still reachable 内存泄露
// free(--g_p2);//如果不free, 将会有 possibly lost 内存泄露
// free(p[1]); //如果不free, 将会有 indirectly lost 内存泄露
// free(p); //如果不free, 将会有 definitely lost内存泄露
return 0;
}
/*
总结:
由局部变量指向的内存,如果不释放为肯定丢失,
由此指针而引起的后续内存泄露,为间接丢失.
由全局变量指向的内存如果不被释放,为still reachable,
如果该变量改动过, 为可能丢失.
是啊,局部变量是栈变量,如果你不能把这个栈变量处理好,出了这个函数,指针地址就丢失了,这就是肯定丢失了.
如果你付给的地址是全局变量,倒是可以访问,叫still reachable
但是如果你这个全局变量的值改动过, 那只有你知道怎样正确访问这块内存,别人可能就访问不到了,这叫可能丢失.
由肯定丢失而引起的进一步的内存丢失为间接丢失.
所以碰到问题你首先要解决什么问题? 肯定丢失, 然后是可能丢失,然后间接丢失,然后still reachable!!!
*/
附上不free时valgrind 的内存错误报告.
hjj@Inspiron:~/MyTest/test1$ valgrind --leak-check=full ./main
==28209== Memcheck, a memory error detector
==28209== Copyright (C) 2002-2013, and GNU GPL'd, by Julian Seward et al.
==28209== Using Valgrind-3.10.1 and LibVEX; rerun with -h for copyright info
==28209== Command: ./main
==28209==
==28209==
==28209== HEAP SUMMARY:
==28209== in use at exit: 106 bytes in 4 blocks
==28209== total heap usage: 4 allocs, 0 frees, 106 bytes allocated
==28209==
==28209== 30 bytes in 1 blocks are possibly lost in loss record 2 of 4
==28209== at 0x4C2AB80: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==28209== by 0x40055E: fun1 (main.c:15)
==28209== by 0x4005AB: main (main.c:23)
==28209==
==28209== 56 (16 direct, 40 indirect) bytes in 1 blocks are definitely lost in loss record 4 of 4
==28209== at 0x4C2AB80: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==28209== by 0x40053F: fun1 (main.c:13)
==28209== by 0x4005AB: main (main.c:23)
==28209==
==28209== LEAK SUMMARY:
==28209== definitely lost: 16 bytes in 1 blocks
==28209== indirectly lost: 40 bytes in 1 blocks
==28209== possibly lost: 30 bytes in 1 blocks
==28209== still reachable: 20 bytes in 1 blocks
==28209== suppressed: 0 bytes in 0 blocks
==28209== Reachable blocks (those to which a pointer was found) are not shown.
==28209== To see them, rerun with: --leak-check=full --show-leak-kinds=all
==28209==
==28209== For counts of detected and suppressed errors, rerun with: -v
==28209== ERROR SUMMARY: 2 errors from 2 contexts (suppressed: 0 from 0)
---------------------
作者：hejinjing_tom_com
来源：CSDN
原文：https://blog.csdn.net/hejinjing_tom_com/article/details/79168749
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