From: Dave Pearson <davep AT hagbard DOT demon DOT co DOT uk>
Newsgroups: comp.os.msdos.djgpp
Subject: Re: More string problems!
Date: Thu, 28 Aug 1997 18:27:31 GMT
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On Thu, 28 Aug 1997 06:32:48 -0800, Kevin Dickerson <kevind AT phs DOT mat-su DOT k12 DOT ak DOT us> wrote:

> Allright, yesterday I posted up some code that would do some stuff
> with strings (that isn't important), 

If you are talking about the message I think you are talking about, it
is, there was some very sage advice and pointers in the followups.

> but now I've encountered the main problem associated with it; it
> strikes me as strange!

There is nothing strange about the problem you have.

> This code (which requires only <stdio.h>):
> 
> main()                                                          
> {                                                               
>    int l1;                                                      
>    char *chr, *buf, *text;

Note that you declare a variable called buff which is a, as yet
unused, pointer to some memory. Currently, no memory is allocated and
pointed to by buf.

Also, note that chr is the same.

>    text = "I Can't Believe It's Not Butter!";

Ok, the pointer called text points someplace.

>    for (l1=0; l1<strlen(text); l1++) 
>    {                                 
>       sprintf( chr, "%c", text[l1] );

At this point you are mis-using the variable 'chr' which was declared
as a pointer to some memory, now you are holding a char value in
it. Ok, it will work, but it's not very clean and IMHO isn't good
practice.

>       strcat( buf, chr );

Stop there! You are now attempting to append the string pointed to by
chr (there isn't one) to the string pointed to by buf (there isn't
one). I'd be suprised if this even ran.

>    }                                                 
>    printf("margarine = \"%s\"\n", buf );             

Won't work either. 'buf' doesn't point to what you think it points to.

> Memory allocation shouldn't be a problem, should it?

This is exactly your problem, you haven't allocated any.

> I'm inclined to believe that it's a problem with strcat(), but I'm
> not positive. Argh!

No, there is no problem with strcat(), there is a problem with your
understanding of strcat(), sprintf() and printf().

>    As I mentioned in my other message, I'm not a newcomer to C, but
> rather to C's blasted string functions. Thanks for your help in
> advance!

Don't take this the wrong way, but if you are having this sort of
problem then you need to learn a bit more about C. In many respects
strings are nothing special in C, they are just memory. The only real
special thing about strings is that there are a set of functions (the
str*() functions and friends) that observe the convention of having a
NUL value as the marker of a string.

I would also suggest that the DJGPP group isn't the correct place for
such questions. A good C book and a group like comp.lang.c might be in
order. BTW, that isn't a flame, it's just a suggestion.

FWIW, here is one way of doing what you appeared to be attempting:

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

int main( void )
{
    char *text = "I Can't Believe It's Not Butter!";
    char *buf  = strdup( text );

    printf( "margarine = \"%s\"\n", buf );

    free( buf );
    
    return( 0 );
}
----------------------------------------------------------------------

There are also many other methods. Have a read of the DJGPP libc info
pages and play close attention to things like malloc(), free(),
strdup(), strcpy(), etc.....

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