malloc char *裏面的函數，valgrind報告內存泄漏

Question

我對C很新，並且在做玩具程序來學習它。 下面的代碼編譯，正確地輸出，但Valgrind的報告內存泄漏：

#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; 
} 

的頂點在頭文件中的編碼，

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

的輸出是：

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

它不打印「free'd記憶」，所以它在哪裏free'd？ 這裏是Valgrind的不得不說一下吧：

==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 

什麼是代碼中的問題？我應該分配不同的頂點名稱嗎？ 感謝您的幫助！

編輯：感謝你們所有人！我已經固定的代碼，我現在不釋放單個元素，即

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

當然和我重新設置爲0，不能相信我忽略了它。非常感謝！

Answer 1

您不會在釋放代碼的循環中重置i。這些循環應該是這樣的：

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

添加了另一個觀點：

free_vertex（）不應該有：

free(ver) 

線，這是別人在說什麼。

free_vertex（）和add_vertex（）應該是並行的，意思是釋放只釋放add中分配的內容。

Answer 2

realloc在這裏是無關緊要的。你這樣做：

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

你不應該釋放數組的單個元素。

Answer 3

你不能free不完全相同的一個你malloc，realloc回來，等等。這是不確定的行爲，你問堆損壞或更壞，如果你做到這一點以外的任何指針。

（有趣的部分：由於arr+0等於arr，一旦你正確地重新初始化i在Francis's answer提到，通過循環的第一次迭代釋放整個陣列從此，你遍歷數組不再是那個存在，這是本身未定義的行爲。）

Answer 4

你必須malloc和free一樣的東西！

你是malloc和realloc一個數組，所以你必須釋放數組。 您正在釋放各個頂點。

Answer 5

問題可能是因爲下面的代碼i未初始化爲零！

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

所以應該

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