From:	"John M. Aldrich" <fighteer AT cs DOT com>
Newsgroups:	comp.os.msdos.djgpp
Subject:	Re: Randon Function
Date:	Tue, 10 Feb 1998 19:03:32 -0500
Organization:	Two pounds of chaos and a pinch of salt.
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Message-ID:	<34E0EAD4.562F@cs.com>
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To:	djgpp AT delorie DOT com
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Richard Chappell wrote:
> 
> >char * read_one_line( char *buf, int len, int seek_line, FILE *fp )
> >{
> [snip]
> >}
> 
> So if I wanted to use this function in a program, would I have:
> 
> char *mypc;
> mypc=read_one_line(&mypc, myLenWanted,myLineWanted,"data.txt");

This won't even have a ghost of a chance of working.  Problems:

1) You don't allocate any space for the buffer, nor do you initialize it
to anything.  This is guaranteed to cause a crash.
2) "data.txt", as Eli pointed out, is not a file pointer; it's a string.

> If I've done this wrongly (which I probably have because I don't
> really know anything about file i/o) please tell me what I did wrong,
> and how to fix it !!

The code I used to test the above function is as follows:

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

/* read_one_line function from above */

int main( int argc, char *argv[] )
{
    char line[10000];
    FILE *fp;
    int n;

    if ( argc < 3 )
        exit( 1 );

    if ( ( fp = fopen( argv[1], "r" ) ) == NULL )
    {
        perror( argv[1] );
        exit( 1 );
    }

    n = atoi( argv[2] );

    if ( read_one_line( line, 10000, n, fp ) == NULL )
        printf( "Line not found.\n" );
    else
        printf( line );

    fclose( fp );
    return 0;
}

This program is invoked with "getxline filename count", where filename
is the name of the file, and count is a number indicating which line to
read.  I named the program 'getxline'.  Note:  the code doesn't check
for the count to be a valid number; if it's anything else, the code will
return garbage in the buffer.  This is a bug in my function, btw; it
should detect seek_line == 0 and return NULL.

-- 
---------------------------------------------------------------------
|      John M. Aldrich       | "Always listen to experts.  They'll  |
|       aka Fighteer I       | tell you what can't be done, and why.|
|   mailto:fighteer AT cs DOT com   | Then do it."                         |
| http://www.cs.com/fighteer/|                - Lazarus Long        |
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