Creating a method to convert a Pascal string in C using pointers

Question

I've been working on a method which is supposed to convert a Pascal string to a C String. I was also told that the char * returned should point to a newly allocated char array containing a null-terminated C-String. The callee is responsible for calling free() on this array.

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

char *pascal_convert(void *x)
{
    int *y;
    x = y;
    char *z;
    *z = *((int*)x);
    char *arr = malloc(sizeof(*z));
    for (int i = 0; i < *y; i++)
    {
        arr[i] = z[i];
    }
    char* fin = arr;

    return fin;
}

I would say the "caller" is responsible for calling free(). — chux
– chux, Commented Dec 8, 2015 at 23:26

chux · Accepted Answer · 2015-12-08 23:25:26Z

2

Many adjustments needed

char *pascal_convert(void *x)
{
    // int *y;
    // x = y;   This assignment is backwards
    unsigned char *y = x;  // Need unsigned char (unless your pascal uses wider type here)

    // y = z;
    // char *z;
    // *z = *((int*)x);
    size_t size = *y++;  // Size is just the first element

    // char *arr = malloc(sizeof(*z));
    char *arr = malloc(size + 1);  // Allocate + 1 for the null chacter

    if (arr) {  // test need as `malloc()` may fail
      // for (int i = 0; i < *y; i++) { arr[i] = z[i]; }
      memcpy(arr, y, size); 
      arr[size] = '\0';  // append null character
    } 

    // char* fin = arr;  // No need for new variable
    // return fin;
    return arr;
}

answered Dec 8, 2015 at 23:25

chux

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2 Comments

Lee Daniel Crocker Over a year ago

You should also replace any NUL characters in the middle of the string with spaces or something--Pascal allows these but C does not.

chux Over a year ago

@Lee Daniel Crocker Agree detection of a '\0' in a pascal string is an important consideration for robust code. Many alternatives exists on how to handle that. IMO, an embedded '\0' should result in a failure. Maybe returning NULL? Or simply also return the size and let the calling code sort it out. Side note: fgets() also gets '\0' and keeps going until '\n' - no error indication.

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