Calling Function with type struct and returning pointer does not run

问题

I'm having trouble running the program, there are no warnings or errors popping up in CodeBlocks. The trouble comes when I create an ArrayList struct of pointer type and try to dynamically allocate memory using malloc. I'm using the syntax '->.' I've been at this for hours with no real leads.

#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;
}

回答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;
}

And you probably do not want to allocate length + 1 elements, because you have r->capacity.

回答2:

you must first initialize Arraylist *r:

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

来源：https://stackoverflow.com/questions/21506725/calling-function-with-type-struct-and-returning-pointer-does-not-run

标签

arrays

function

pointers

struct