Question

I am trying to append a string to a text file, but I am getting odd characters.
If I try to print out my result to the console, output is regular.
This is what i see as the output in vim. If I look at it in gedit I get strange boxes.

Output File:

  A^CA^BB^A
  A^CB^BA^A
  B^CA^BA^A

Expected Output:

AAB
ABA
BAA

My function should write out the permutations with no duplicates into a text file.

Code For Function:

void RecursivePermute (char *prefix, char *rest, int *ptr)
{
    char *temp = malloc(sizeof(char *));
    char *new_prefix = malloc(sizeof(char *));
    char *rest_left = malloc(sizeof(char *));
    char *rest_right = malloc(sizeof(char *));
    char *new_rest = malloc(sizeof(char *));
    char rest_char;
    int idx = 0;
    int first_occurance = 0;
    int i;
    FILE *file;
    strcpy(temp, rest);
    if (*rest == '\0')
    {
        *ptr += 1;
        printf("Permutation %d: %s\n", *ptr, prefix);
        file = fopen("permutations.txt", "a");
        fprintf(file,"%s\n",prefix);
        fclose(file);
        return;
    }
    else
    {
        size_t rest_size = strlen(rest);
        while (*rest != '\0')
        {

            first_occurance = (strchr(temp, *rest) - temp - idx);
            if (first_occurance == 0)
            {
                rest_char = *rest;
                rest_left = strncpy(rest_left, rest-idx, idx);
                rest_right = strncpy(rest_right, rest+1, rest_size-1);
                sprintf(new_rest, "%s%s", rest_left, rest_right);
                sprintf(new_prefix,"%s%s", prefix, &rest_char);
                RecursivePermute( new_prefix, new_rest, ptr);
            }
            rest++;
            idx ++;
        }
    }
}

Answer 1

One thing is that your printf format specifier for &rest_char is wrong. &rest_char can’t be interpreted as a string because it is not null-terminated. If you want to print out a character use %c. Your line should look like this:

sprintf(new_prefix,"%s%c", prefix, rest_char);

Also you might want to look and see how you are allocating strings. By specifying a size of sizeof(char *) it will only create a memory allocation the size of a pointer. If the string in rest is greater than that it will cause a buffer overrun when you do the strcpy.