我正在尝试用 C 编写数据结构堆栈。堆栈的每个元素都是一个字符串。以下是我使用的三个文件。第一个是主要的,其他的是头文件 stack.h 和文件 stack.c。我将 stackElement 声明为指向该元素的指针。 stackT 是定义堆栈的结构。当我尝试释放分配内存时出现了我的问题,因为当我运行 valgrind 时我得到了
==31235== ERROR SUMMARY: 2 errors from 2 contexts (suppressed: 0 from 0)
==31235==
==31235== 1 errors in context 1 of 2:
==31235== Invalid free() / delete / delete[] / realloc()
==31235== at 0x4C2BDEC: free (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==31235== by 0x400893: StackDestroy (in /test)
==31235== by 0x400B61: main (in /test)
==31235== Address 0x51fc150 is 0 bytes inside a block of size 4 free'd
==31235== at 0x4C2BDEC: free (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==31235== by 0x400B55: main (in /test)
24 bytes in 1 blocks are definitely lost in loss record 1 of 1
你能帮帮我吗?
int main(){
stackT S;
int r = 3, i;
StackInit(&S, 2, r);
printf("test\n");
stackElementT s0;
s0 = malloc((r + 1) * sizeof(unsigned char));
memset(s0, 1, r + 1);
s0[r] = 0;
for (i = 0; i < r; i++) {
s0[i] = random() & 0xff;
}
StackPush(&S, s0);
free(s0);
StackDestroy(&S);
return 0;
}
堆栈.h
typedef unsigned char * stackElementT;
typedef struct {
stackElementT *contents;
int maxSize;
int top;
} stackT;
堆栈.c
void StackInit(stackT *stackP, int maxSize, int r) {
stackElementT *newContents;
int i;
r = 3;
newContents = malloc(sizeof(stackElementT) * maxSize);
if (newContents == NULL) {
fprintf(stderr, "Insufficient memory to initialize stack.\n");
exit(1);
}
for (i = 0; i < maxSize; i++) {
if ((newContents[i] = malloc(r * sizeof(stackElementT))) == NULL) {
fprintf(stderr, "Insufficient memory to initialize stack.\n");
exit(1);
}
}
stackP->contents = newContents;
stackP->maxSize = maxSize;
stackP->top = -1; /* I.e., empty */
}
void StackDestroy(stackT *stackP) {
int i;
for (i = 0; i < stackP->maxSize; i++)
free(stackP->contents[i]);
free(stackP->contents);
stackP->contents = NULL;
stackP->maxSize = 0;
stackP->top = -1;
}
void StackPush(stackT *stackP, stackElementT element) {
if (StackIsFull(stackP)) {
fprintf(stderr, "Can't push element on stack: stack is full.\n");
exit(1);
}
stackP->contents[++stackP->top] = element;
}
编辑:
使用下面的答案我评论了 free(s0) 行,但我现在得到下一个错误:
==31855== 24 bytes in 1 blocks are definitely lost in loss record 1 of 1
==31855== at 0x4C2AB80: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==31855== by 0x4007F9: StackInit (in /test)
==31855== by 0x400AA9: main (in /test)
最佳答案
第一个 valgrind 消息非常清楚:您将释放同一 block 内存两次,第一次是在 main
中使用 free(s0)
,第二次是在堆栈销毁
。更改您的代码以使其不这样做 - 要么让堆栈获得对象的所有权(因此它释放它们而 main
不这样做),反之亦然(堆栈不占用对象的所有权并且不释放它们)。
“ block 丢失”问题是因为您在 StackInit
的循环中为每个堆栈槽分配了内存块,并且 StackPush
覆盖了指针,因此您永远无法释放分配给已用栈槽的原始内存。这里至少也有两种可能的解决方案:不要在 StackInit
中预先分配内存块(只需在 StackPush
中复制指针),或者复制元素 StackPush 中的 >data(而不是指针)。
关于c - Valgrind block 丢失,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/29811047/