In C How can I convert an int to a char[] without using snprintf or itoa?

Question

Pulling my hair out here, but I need to convert an int to a string in C without using snprintf or itoa. Any suggestions?

I tried using:

/*
**  LTOSTR.C -- routine and example program to convert a long int to
**  the specified numeric base, from 2 to 36.
**
**  Written by Thad Smith III, Boulder, CO. USA  9/06/91 
**  and contributed to the Public Domain.
**  
**  src: http://www8.cs.umu.se/~isak/snippets/ltostr.c
*/

#include <stdlib.h>

char *                  /* addr of terminating null */
ltostr (
    char *str,          /* output string */
    long val,           /* value to be converted */
    unsigned base)      /* conversion base       */
{
    ldiv_t r;           /* result of val / base */

    if (base > 36)      /* no conversion if wrong base */
    {
        str = '\0';
        return str;
    }
    if (val < 0)    *str++ = '-';
    r = ldiv (labs(val), base);

    /* output digits of val/base first */

    if (r.quot > 0)  str = ltostr (str, r.quot, base);

    /* output last digit */

    *str++ = "0123456789abcdefghijklmnopqrstuvwxyz"[(int)r.rem];
    *str   = '\0';
    return str;
}

...but it gives me a EXE_BAD_ACCESS on *str++ = "0123456789abcdefghijklmnopqrstuvwxyz"[(int)r.rem];.

You might get some clues from my question: http://stackoverflow.com/questions/4351371/c-performance-challenge-integer-to-stdstring-conversion The answers all use some C++, but the underlying approaches work in C as well. — Ben Voigt, May 23 '11 at 00:23
actually, it seems like this code does work after all. Sorry. — Ash, May 23 '11 at 00:29
There is a implementation for itoa here : http://www.opensource.apple.com/source/groff/groff-12/groff/libgroff/itoa.c — Waxhead, May 23 '11 at 00:35
Note that the code shown fails badly on LONG_MIN (on machines that use a 2's-complement representation for integers). — Jonathan Leffler, May 23 '11 at 04:02

score 3 · Accepted Answer · answered May 23 '11 at 00:24

3

I'm guessing you're not allocating any memory.

str needs to be a pointer to a block of allocated memory sufficiently large enough to fit the string being created by the function.

This function doesn't allocate any memory. You need to do that before you call the functio, and then pass the pointer in.

answered May 23 '11 at 00:24

Andrew Cooper

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Notice how the mistake mimics the mistake in the statement of the question title (converting an int to a pointer versus converting an int to a string). – R.. GitHub STOP HELPING ICE May 23 '11 at 01:58
Also notice that the number of digits needed to represent `x` in base `B` equals `logB(x)+1`. – Philip May 23 '11 at 10:46

In C How can I convert an int to a char[] without using snprintf or itoa?

1 Answers1