Passing a 2D pointer

[Stack Overflow]

Hello,

I have run into a problem. I am trying to pass a two dimensional pointer and write data to it. The only thing is it always crashes if I write more than one array index. For example:

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

void passtest(char ***string) {
	// Two strings
	*string = (char **)malloc(sizeof *string * 2);

	if (*string) {
		// Works great
		(*string)[0] = (char *)malloc(sizeof *string[0] * 6);
		strcpy(*string[0], "Hello");

		// Crashes...
		(*string)[1] = (char *)malloc(sizeof *string[1] * 3);
		strcpy(*string[1], "Hi");
	}
}

int main() {
	int i;
	char **test = NULL;

	passtest(&test);

	for (i = 0; i < 2; i++)
		free(test[i]);
	free(test);

	return 0;
}

It may be something im doing wrong, or not allocating enough space. I don't know, thats why I'm here I've spent 30 minutes trying to figure it out and still have no clue.


Thank you for your time,
- Stack Overflow

[Thantos]

First things first, remove the cast from the return of malloc()

[Salem]

You forgot some parentheses

void passtest(char ***string)
{
    // Two strings
    *string = (char **) malloc(sizeof *string * 2);

    if (*string) {
        // Works great
        (*string)[0] = (char *) malloc(sizeof *string[0] * 6);
        strcpy((*string)[0], "Hello");

        // Crashes...
        (*string)[1] = (char *) malloc(sizeof *string[1] * 3);
        strcpy((*string)[1], "Hi");
    }
}

void passtest2(char ***string)
{
    char **temp;
    temp = malloc(sizeof *temp * 2);
    if (temp) {
        temp[0] = malloc(sizeof *temp[0] * 6);
        strcpy(temp[0], "Hello");
        temp[1] = malloc(sizeof *temp[1] * 3);
        strcpy(temp[1], "Hi");
    }
    *string = temp;
}

I prefer the second form - use a temp variable of the correct type, then perform the assignment to the input pointer at the end. It removes one layer of indirection in the body of the code, making things just a little bit simpler.

Oh, and watch the casts on the return result of malloc - bad idea in C - see the FAQ

[Stack Overflow]

Edit: Reading Salem's post now.

[Stack Overflow]

Thanks Salem,

It works now


- Stack Overflow