Thread: Dynamicly resize array of strings

I've made a simple demo (see below) that calls a function which adds some strings to an array. What I don't understand is why if I comment the malloc statements in the addSomeStrings function, everything still works ok. Is this just by chance or are those statements not needed?

I ask because I have something similar in an application I am developing which works fine without the malloc statements but with them it throws a segmentation fault when i try and display the strings in the array (output of strtok function).

Any help would be most appreciated.

Code:

    void addSomeStrings(char **data)
    {
        printf("Allocating heap space\n");
        data[0] = (char *) malloc(5*sizeof(char *));
        data[0] = "first";
        
        printf("Reallocating heap space\n");
        data = (char **) realloc(data, 2 * sizeof(char *));
        data[1] = (char *) malloc(6*sizeof(char *));
        data[1] = "second";
        
        printf("Reallocating heap space\n");
        data = (char **) realloc(data, 3 * sizeof(char *));
        data[2] = (char *) malloc(5*sizeof(char *));
        data[2] = "third";
        
    }

    int main()
    {
        char **data;
        int i=0;
        
        data = (char **)malloc(sizeof(char *));
        
        addSomeStrings(data);
            
        for (i=0; i<3; i++)
        {
            printf("String %s\n", data[i]);
        }
        
        return 0;
    }

Thanks for the reply, I understand now about using strcpy, and I see now why realloc will not change the value in the caller - but I am not sure how to fix it. Should I change the function to accept char *** ?

I've modified my code and set it to run in a loop so I can check if it eats memory, and it doesn't. I think it's correct now - any comments would be very welcome!

Code:

    void addSomeStrings(char ***input)
    {
        char **data;
        
        data = (char **) realloc(*input, 1 * sizeof(char *));
        data[0] = (char *) malloc(6*sizeof(char *));
        strcpy(data[0], "first");
        
        data = (char **) realloc(data, 2 * sizeof(char *));
        data[1] = (char *) malloc(7*sizeof(char *));
        strcpy(data[1], "second");
        
        data = (char **) realloc(data, 3 * sizeof(char *));
        data[2] =  malloc(6*sizeof(char ));
        strcpy(data[2], "third");

    }
    
    int main()
    {
        char **data;
        
        while (1)
        {
            /* Allocate space for array */
            data = (char **)malloc(sizeof(char *));
            
            /* Add 3 strings */
            addSomeStrings(&data);
            
            /* Free pointers to each string */
            free(data[0]);
            free(data[1]);
            free(data[2]);
            
            /* Free initial pointer */
            free(data);
            
            usleep(10000);
        }
            
        
        return 0;
    }

Thanks - that worked a treat.

You're basically being lucky at the moment

I guessed something like this was going on as in my larger application it was segfaulting, now it works fine.