From: Alicia Carla Longstreet <carla AT ici DOT net>
Newsgroups: comp.os.msdos.djgpp
Subject: Re: Problem with strncpy (DJGPP in msdos window in win95)
Date: Sat, 27 Sep 1997 16:22:31 -0400
Organization: The Computer Solution
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Message-ID: <342D6B07.5BA9@ici.net>
References: <EGwqnM DOT 2v2 AT csc DOT liv DOT ac DOT uk>
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Paul Fitzgibbons wrote:
> 
> Hi there
> 
> just like to say that I am enjoying learning with DJGPP and have also got
> the Allegro Library from Shawn Hargreaves.
> 
> I have a problem with the following code. When inputting strings of up to 20
> chars there doesnt appear to be a problem but if i input a string of length
> 21 or greater the string then ends in funny characters. I thought strncpy
> would have avoided this? I am able to write a function to check if the
> length is greater and to loop if it is, but i would rather do it by
> shortening the string.
> 
> Any help will be much appreciated.
> 
> Many thanks Paul Fitz
> 
> [code follows]
> 
> #include <stdio.h>
> #include <string.h>
> #include <stdlib.h>
> 
> struct DETAIL
> {
>    char name[21]; //max length +1 for NULL
> };
> 
> void dispstru(struct DETAIL *ptr);
> 
> main()
> {
>    struct DETAIL Personal_info;
>    struct DETAIL *Personal_info_ptr;
>    char buff[1024];  //nice and long to avoid errors
> 
>    printf("What is the name? : ");
>    gets(buff);
> 
>    strncpy(Personal_info.name,buff,20); //copy 20 chars
> 
>    printf("name is : %s",Personal_info.name);
> 
>    Personal_info_ptr=&Personal_info;
>    dispstru(Personal_info_ptr);
> }
> 
> void dispstru(struct DETAIL *ptr)
> {
>    printf("Pointer to name = : %s ",ptr->name);
> }

Your problem is when the length of the string to be copied is longer
than 20 characters strncpy() does NOT place a terminator on the
resulting string.  You will have to do that yourself.  This behavior is
in accord with the ANSI/ISO Standard.

BTW, If you use fgets() instead of gets() you can specify the length of
the input.

fgets(buffer, 21, stdin );

gets() is a really horrible function an should probably never be used.

-- 
************************************************
*  Alicia Carla Longstreet     carla AT ici DOT net   *
*    Remove the _JUNK_ when replying to me.    *
************************************************
My programming is Wobbly. It's good programming but it Wobbles,
and the statements sometimes get in the wrong places.
************************************************
C appeals due to is simplicity and elegance.