Question

我在运行程序时遇到问题，CodeBlocks中没有出现警告或错误。当我创建指针类型的ArrayList结构并尝试使用malloc动态分配内存时，就会遇到麻烦。我正在使用语法' - ＆gt;。'我已经在这几个小时没有真正的线索了。

#include <stdio.h>
#include <string.h>
#define DEFAULT_INIT_LEN 10//this is in another header file

typedef struct ArrayList{//this is also in another header file
    char **array;
    int size;
    int capacity;
} ArrayList;

int main(void){
    ArrayList *test=createArrayList(12);
    printf("size: %d capacity: %d\n", test->size, test->capacity);
}

ArrayList *createArrayList(int length){
    int i=0;//index variables
    ArrayList *r;
    if (length>DEFAULT_INIT_LEN){
        r->array=malloc(sizeof(char)*(length+1));//create memory for internal array
        r->capacity=length;
        r->size=0;
        for (i=0; i<length; i++)//sets members in the array to NULL
            r->array[i]=NULL;
        printf("Created new ArrayList of size %d\n", length);
    }
    else{
        r->array=malloc(sizeof(char)*(DEFAULT_INIT_LEN+1));//create memory for internal    array
        r->capacity=DEFAULT_INIT_LEN;
        r->size=0;
        for (i=0; i<DEFAULT_INIT_LEN; i++)//sets members in the array to NULL
            r->array[i]=NULL;
        printf("Created new ArrayList of size %d", DEFAULT_INIT_LEN);
    }
    return r;
}

Answer 1

ArrayList *
createArrayList(int length)
{
    ArrayList *r = malloc(sizeof(*r));
    if (r == NULL) return NULL;

    length = MAX(length, DEFAULT_INIT_LEN); // do not duplicate code. ever.

    r->array = calloc(length + 1, sizeof(r->array[0]));
    if (r->array == NULL) { free(r); return NULL; } // always check pointers

    r->size = 0;
    r->capacity = length;

    printf("Created new ArrayList of size %d\n", length);

    return r;
}

您可能不想分配length + 1元素，因为您有r->capacity。

Answer 2

你必须先初始化Arraylist * r：

ArrayList *createArrayList(int length){
int i=0;//index variables
ArrayList *r=malloc(sizeof(ArrayList);

使用类型struct和返回指针调用函数不会运行

2 个答案: