C-包含字符串的表的动态内存分配

Question

I try to make the memory allocation dynamically for table that contains the strings.
In my case, I have to use it dynamically, because I don't know how rows and columns the program will get.
Here is my code for two function:
1.The first is allocating the memory for the table only.
2.The second should free all allocated memory.
3.In the main function I'm allocating the memory for the string and copy the part of the predefined string (it's dummy code, for example only)

The result is "Runtime error" What am I doing wrong in the code?

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

char *** buildOptions(int rows, int columns) {
    int i=0;
    printf("1...\n");
    char ***options = (char ***)malloc(rows * sizeof(char **));
    printf("2...\n");
    for(i=0; i<rows; i++) {
        printf("3...\n");
        options[i] = (char **)malloc(columns * sizeof(char *));
        printf("4...\n");
    }
    return options;
}

void freeOptions(char ****options, int rows, int columns) {
    int i, j;
    for(i=0; i<rows; i++) {
        for(j=0; j<columns; j++) {
            if(*options[i][j])
                free(*options[i][j]);
        }
        if(*options[i]) {
            free(*options[i]);
        }
    }
    free(*options);
}

int main(void) {
    int i, j, k;
    char * str = "123456789abcdefghjkl\0";
    char ***options = buildOptions(5, 3);
    printf("Starting...\n");
    for(i=0; i<5; i++) {
        for(j=0; j<3; j++) {
            options[i][j] = (char *)calloc((i+j+2)+1, sizeof(char));
            strncpy(options[i][j], str, i+j+2);
        }
    }

    for(i=0; i<5; i++) {
        for(j=0; j<3; j++) {
            printf(">>options[%d][%d]=%s<<\n", i,j, options[i][j]);
        }
    }

    freeOptions(&options, 5, 3);

    //here I want to check if the memory is freed
    for(i=0; i<5; i++) {
        for(j=0; j<3; j++) {
            printf(">>options[%d][%d]=%s<<\n", i,j, options[i][j]);
        }
    }


    return 0;
}

Answer 1

Change the declaration of freeOptions to

void freeOptions(char ***options, int rows, int columns)

the call to

 freeOptions(options, 5, 3);

and the call to free() inside the freeOptions to

  free(options[i][j]);

Answer 2

The cause of your segmentation fault is in how you access the array in freeOptions :

*options[i][j]

is the same as:

*(options[i][j])

bot options is the address of your options in main , so you should dereference options` first:

(*options)[i][j]

There's actually no need to pass in the char ***options from main by reference unless you plan to set *options to NULL in freeOptions . A better way to implement freeOptions has been pointed out in the other Michael's answer.

//here I want to check if the memory is freed

You can't find out whether the free has succeeded by accessing now invalid memory and causing undefined behaviour. The data may still be there, but it might as well contain garbage.