Question

我对C很陌生，正在做玩具程序来学习它。以下代码编译，输出正确，但Valgrind报告内存泄漏：

#include <stdlib.h>
#include <string.h>
#include <stdio.h>
#include "graph.h"

void add_vertex(vertex *v_p, char *name) {
    if(strlen(name) == 0) { 
        printf("error");
    }
    v_p->name = (char *)malloc(strlen(name) + 1);
    if(v_p->name == NULL) {
        printf("error");
    }
    strcpy(v_p->name, name);
    v_p->cluster = -1;
    v_p->deleted = 0;
    printf("added vertex.\n");
}

void free_vertex(vertex *ver) {
    if(ver->name) {free(ver->name);printf("free'd name\n");}
    free(ver);

}

int main() {
    int Nu = 0;
    vertex *arr = (vertex *)malloc(2 * sizeof(vertex));
    vertex *_temp;
    int i =0;
    add_vertex(arr, "Hello");
    add_vertex(arr+1, "World");
    _temp = (vertex *)realloc(arr, 4*sizeof(vertex));
    printf("reallocated\n");
    if (_temp != NULL) {
        arr = _temp;
        add_vertex(arr+2, "this");
        add_vertex(arr +3, "worked");
        Nu=4;
    }
    else{
        printf("FAIL\n");
        Nu=2;
    }
    for (; i <Nu; i++) {
        printf("%s\n",(arr+i)->name);
    }
    for (; i <Nu; i++) {
       free_vertex(arr+i);
    }
    free(arr);
    return 0;
}

顶点编码在头文件中，

typedef struct vertex_t
{
    char*   name;
    int     cluster;
    int    deleted;
}vertex

输出结果为：

added vertex.
added vertex.
reallocated
added vertex.
added vertex.
Hello
World
this
worked

它不会打印“free'd memory”，所以它在哪里免费？这是Valgrind不得不说的：

==1436== HEAP SUMMARY:
==1436==     in use at exit: 24 bytes in 4 blocks
==1436==   total heap usage: 6 allocs, 2 frees, 120 bytes allocated
==1436== 
==1436== 5 bytes in 1 blocks are definitely lost in loss record 1 of 4
==1436==    at 0x4C2893D: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==1436==    by 0x4006C3: add_vertex (graph.c:10)
==1436==    by 0x4007EF: main (graph.c:37)
==1436== 
==1436== 6 bytes in 1 blocks are definitely lost in loss record 2 of 4
==1436==    at 0x4C2893D: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==1436==    by 0x4006C3: add_vertex (graph.c:10)
==1436==    by 0x400797: main (graph.c:31)
==1436== 
==1436== 6 bytes in 1 blocks are definitely lost in loss record 3 of 4
==1436==    at 0x4C2893D: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==1436==    by 0x4006C3: add_vertex (graph.c:10)
==1436==    by 0x4007AC: main (graph.c:32)
==1436== 
==1436== 7 bytes in 1 blocks are definitely lost in loss record 4 of 4
==1436==    at 0x4C2893D: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==1436==    by 0x4006C3: add_vertex (graph.c:10)
==1436==    by 0x400804: main (graph.c:38)
==1436== 
==1436== LEAK SUMMARY:
==1436==    definitely lost: 24 bytes in 4 blocks
==1436==    indirectly lost: 0 bytes in 0 blocks
==1436==      possibly lost: 0 bytes in 0 blocks
==1436==    still reachable: 0 bytes in 0 blocks
==1436==         suppressed: 0 bytes in 0 blocks

代码有什么问题？我应该以不同的方式分配顶点的名称吗？谢谢你的帮助！

编辑：谢谢大家！我修改了代码，现在我没有释放单个元素，即

void free_vertex(vertex *ver) {
    if(ver->name) {free(ver->name);printf("free'd name\n");}
}

当然重新将i设置为0.不能相信我忽略了它。非常感谢！

Answer 1

您没有在释放代码的循环中重置i。这些循环应如下所示：

for (i = 0; i <Nu; i++) {
    printf("%s\n",(arr+i)->name);
}
for (i = 0; i <Nu; i++) {
   free_vertex(arr+i);
}

又增加了一点：

free_vertex（）不应该有：

free(ver)

行，这是其他人所说的。

free_vertex（）和add_vertex（）应该是并行的，即free只释放add中分配的内容。

Answer 2

realloc在这里无关紧要。你这样做了：

arr = malloc(4 * sizeof(vertex));
for (int i = 0; i < 4; ++i) {
    free(arr[i]);
}
free(arr);

你不应该释放数组中的单个元素。

Answer 3

你不能free除malloc，realloc之类的完全相同的指针之外的任何指针。这是未定义的行为，你要求堆损坏或者更糟，如果你这样做。

（有趣的部分：由于arr+0等于arr，一旦你按照Francis's answer中的提法正确重新启动i，循环的第一次迭代将释放整个数组从那时起，你将迭代一个不再存在的数组，这本身就是未定义的行为。）

Answer 4

您必须malloc和free相同的事情！

您是malloc和realloc数组，因此您必须释放数组。你释放了各个顶点。

Answer 5

问题可能是因为以下代码i未初始化为零！

for (; i <Nu; i++) {
    printf("%s\n",(arr+i)->name);
}
for (; i <Nu; i++) {
   free_vertex(arr+i);
}

所以它应该是

for (; i <Nu; i++) {
    printf("%s\n",(arr+i)->name);
}
for (i=0 ; i <Nu; i++) {
   free_vertex(arr+i);
}

malloc char *在函数内部，valgrind报告内存泄漏

5 个答案: