c - 扩展动态分配的指针数组

Question

这真是太痛苦了。我试图动态分配一个数组并使用 realloc、calloc 和 malloc，但这三个方法都没有给我带来任何结果。看起来我已经成功扩展了它，但我无法正确复制它。扩展函数中的所有内容都很好，但在我调用该函数后，它就变得毫无用处。

typedef struct ArrayList
{
    // We will store an array of strings (i.e., an array of char arrays)
    char **array;

    // Size of list (i.e., number of elements that have been added to the array)
    int size;

    // Length of the array (i.e., the array's current maximum capacity)
    int capacity;

} ArrayList;

ArrayList *expandArrayList(ArrayList *list, int length){
    struct ArrayList *temp=realloc(list, length);
    if (length<list->capacity){
        return NULL;
        free(temp);
    }
    if (temp)
        list=temp;
    else{
        free(temp);
        return NULL;
    }
    list->capacity=length;
    printf("-> Expanded ArrayList to size %d.\n", length);
    return list;
}

Answer 1

我猜您实际上想扩展 ArrayList 中 array 的容量。那么函数应该是这样的:

#include <errno.h>
ArrayList *expandArrayList(ArrayList *list, int new_capacity){
    if (list->capacity >= new_capacity) {
        return list; // If a smaller capacity is passed in, do nothing.
    }

    char **tmp = realloc(list->array, new_capacity * sizeof(char*));
    if (tmp) {
        list->capacity = new_capacity;
        list->array = tmp; // On success, set 'array' field of 'list' to tmp.
    } else {
        if (errno == ENOMEM) {
            fprintf(stderr, "Error: not enough memory.\n"); // On failure, report the error and exit.
            exit(1);
        }
    }

    return list;  
}

我还没有测试过代码，但希望这对你有帮助。