c - 结构与 ptr 数组嵌套结构分配和内存分配

Question

我有一个结构，其中包含指向也包含指针的相关结构的深度嵌套。我在正确初始化时遇到问题，因为 ptrs 数组必须将大小传递给 init 函数。见下面的代码:

类型定义:

typedef struct tuple Tuple;
typedef struct dict Dict;
int findKey(Dict *d, char *check);

struct tuple {
    char                   *key;           //named loc
    void                   *val;           //data
};

struct dict {
    unsigned int           size;           //max size
    unsigned int           counter;        //# tuples
    Tuple                  **entries;     //list of tuples
};

初始化函数:

Dict *initDict(const unsigned int size) {
    Dict data = {.size = size, .counter = 0, .entries = (Tuple**) malloc(sizeof(Tuple*) * size)};
    for (unsigned int i = 0; i < size; i++) {
        data.entries[i] = (Tuple*) malloc(sizeof(Tuple));
        data.entries[i]->key = '\0'; /* initially null */
        data.entries[i]->val = '\0'; /* initially null */
    }
    Dict *d = (Dict*) malloc(sizeof(Dict));
    d = &data;
    return d;
}

字典操作:

short setTuple(Dict *d, char *key, void* val) {
    int i;
    if ((i = findKey(d, key)) != -1) { /* found key */
        d->entries[i]->val = val;
        return 0;
    }
    else {  /* new entry */
        if (d->counter < d->size) { /* find first null */
            for (unsigned int i = 0; i < d->size; i++) {
                if (d->entries[i]->key == NULL) break;
            } /* then replace null slot */
            d->entries[i]->key = (char *) malloc(sizeof(char) * strlen(key));
            d->entries[i]->key = key;
            d->entries[i]->val = (void *) malloc(sizeof(&val));
            d->entries[i]->val = val;
            d->counter++;
            return 0;
        }
        return -1; /* no room */
    }
}

short setTuples(Dict *d, char *json) {

}

void* getTuple(Dict *d, char *key) {
    int i;
    if ((i = findKey(d, key)) != -1) {
        void *val = d->entries[i]->val;
        return val;
    } return (void *) -1; /* not found */
}

void* getIndex(Dict *d, unsigned int index) {
    if (index < d->counter && d->entries[index]->key != NULL) {
        void *val = d->entries[index]->val;
        return val;
    } return (void *) -1; /* not found */
}

/* TODO: add checks for NULL ptr prior to freeing? */
int removeTuple(Dict *d, char *key) {
    int i;
    if ((i = findKey(d, key)) != -1) {
        free(d->entries[i]->key);
        free(d->entries[i]->val);
        free(d->entries[i]);
        d->entries[i]->key = '\0';
        d->entries[i]->val = '\0';
        d->counter--;
        return 0;
    } return -1; /* no room */
}

void destroyDict(Dict *d) {
    for (unsigned int i = 0; i < d->counter; i++) {
        free(d->entries[i]->key);
        free(d->entries[i]->val);
        free(d->entries[i]);
        d->entries[i]->key = '\0';
        d->entries[i]->val = '\0';
        d->entries[i] = '\0';
        d->counter--;
    }
    free(d->entries);
    free(d);
}

/* return index of tuple in dict or -1 if DNE */
int findKey(Dict* d, char* check) {
    unsigned int i;
    for (i = 0; i < d->counter; i++) {
        if (d->entries[i]->key != NULL && strcmp(d->entries[i]->key, check) == 0) {
            return i;
        }
    } return -1; /* not found */
}

Answer 1

Dict *initDict(const unsigned int size) {
    Dict data = { /*...*/ };
    // ...
    Dict *d = (Dict*) malloc(sizeof(Dict));
    d = &data;
    return d;
}

这里存在两个明显的问题:

1. d = &data; 会立即泄漏您使用 malloc 分配的内存。
2. return d; 从 (1) 继续，您返回局部变量的地址。因此，您的程序行为未定义。

如果您想使用您在局部变量中设置的值复制初始化新分配的内存，则需要取消引用该指针，然后分配指针对象:

Dict *initDict(const unsigned int size) {
    Dict data = { /*...*/ };
    // ...
    Dict *d = malloc(sizeof(Dict));
    if(d)
      *d = data;
    else {
      // Everything you allocated for data must be cleaned here.
    }
    return d;
}

当您的原始代码使用 malloc 时，我还添加了您非常想念的检查。检查指针不为 NULL!