Question

我有两种结构：

struct product {
    char *title;  // Name of the product
    char code[8]; // Max. 7 characters of product ID
    int stock;  // Current stock (number of units)
    double price;  // Price of a single unit
};

struct product_array {
    struct product *arr;
    unsigned int count;
};

我正在使用函数将产品添加到product_array：

void add_product(struct product_array *pa, const char *title, const char *code,
        int stock, double price) {
    pa->count++;
    struct product* nProduct = malloc(sizeof (struct product));
    if (!nProduct) free(nProduct);
    init_product(nProduct, title, code, stock, price); 

    pa->arr = realloc(pa->arr, (pa->count) * sizeof (struct product));
    if (!pa->arr) free(pa->arr);

    pa->arr[pa->count - 1] = *nProduct;
}

void init_product(struct product *pr, const char *title, const char *code,
        int stock, double price) {
    int titleLen = strlen(title);
    int codeLen = strlen(code);
    char *aTitle = calloc((1 + titleLen) * sizeof (char), 1);
    strncpy(aTitle, title, titleLen);
    char* codePtr = strncpy(pr->code, code, codeLen);
    if (codeLen <= 7)
        *(codePtr + codeLen) = 0;
    else
        *(codePtr + 7) = 0;
    pr->title = aTitle;
    pr->stock = stock;
    pr->price = price;
}

add_product在main.c中的工作方式如下

struct product_array pa;
pa.count = 0;
pa.arr = NULL;

struct product p;
init_product(&p, "test", "0000", 1, 0.50);

print_products(&pa);


add_product(&pa, "Product 1", "0000", 0, 10);
add_product(&pa, "Long name, isn't it", "1234567890", 10, 100);
add_product(&pa, "Product 3", "9999999", 0, 20);

print_products(&pa);
remove_all(&pa);

当我试图释放所有已分配的内存时，我遇到了问题。这是删除所有功能：

int remove_all(struct product_array *pa) {
    unsigned int i;
    unsigned int until = pa->count;
    struct product *prdPtr = pa->arr;
    struct product *next;
    for (i = 0; i < until; i++) {
        next = prdPtr + 1;
        free(prdPtr->title);
        free(prdPtr);  // this raises error
        prdPtr = next;
    }
    if (pa->arr != NULL) {
        free(pa->arr);
    }    
    pa->count = 0;
    return 1;
}

for循环溢出，但我现在试图弄清楚在这种情况下释放内存的逻辑。在remove_all函数中，我想释放product_array的所有内存。我正在迭代数组中的每个（struct）产品并释放title的内存。在释放标题记忆后，我试图释放结构产品本身。它在第一次迭代中起作用，但是当我来到第二个元素时，标题可以被释放但是free（prdPtr）会引发SIGABRT。

我可能会缺少什么？为什么我能够释放产品的标题而不是产品本身？提前谢谢你的帮助。

Answer 1

pa->arr为struct product *而不是struct product **。所以你为pa->arr分配了内存，你应该只释放一次。 pa->arr[i]不是指针，而只是一个结构。

你不应该释放它，但你应该释放分配给其成员的任何内存，例如title。

所以将你的for循环更新为

...
for (i = 0; i < until; i++) {
        next = prdPtr + 1;
        free(prdPtr->title); //just free members
        prdPtr = next;
    }
if (pa->arr != NULL) {
    free(pa->arr);
}    
...

修改

另请注意，add_product中存在不必要的malloc。建议修复：

void add_product(struct product_array *pa, const char *title, const char *code, int stock, double price) { struct product *pa_tmp; pa->count++; pa_tmp = realloc(pa->arr, (pa->count) * sizeof (struct product)); if (pa_tmp == null) { /* handle out of memory error */ } pa->arr = pa_tmp; init_product(&pa->arr[pa->count - 1], title, code, stock, price); }

Answer 2

两次释放相同的内存块：

// this makes pdrPtr to an alias of pa->arr
struct product *prdPtr = pa->arr;

for (i = 0; i < until; i++) {
    ...
    free(prdPtr);  // free prdPtr a.k.a. pa->arr
    ...
}
    // here you free the same oject again.
    free(pa->arr);

删除最后一个free(pa->arr);。

释放struct array的内存

2 个答案: