Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!ames!hc!lll-winken!uunet!portal!cup.portal.com!Tim_CDC_Roberts
From: Tim_CDC_Roberts@cup.portal.com
Newsgroups: comp.lang.c
Subject: Re: Problem returning doubles from a function
Message-ID: <16197@cup.portal.com>
Date: 25 Mar 89 00:46:13 GMT
References: <39722@csvax1.cs.tcd.ie>
Organization: The Portal System (TM)
Lines: 50

In <39722@csvax1.cs.tcd.ie>, omahony@csvax1.cs.tcd.ie (Donal O'Mahony) writes:

> Can anone explain the problem with the following program (made up of
> 2 files).
>
> ::main.c
> #include <stdio.h>
> main()
> {double a,b;
>
>   a = 1.234;
>   b = store_length(a);
>   printf("b=%f\n",b);
> }
>
> ::rt1.c
> double store_length( double measurements)
> {  measurements= 2;
>   printf("Returning measurements=%f\n",measurements);
>   return(measurements);
> }
>
> When these two programs are linked and run, they do not print 'b=2,'
> as I would expect.  Why?

Once again, I am sure there will be 24 other replies to this, all of which
will cross in the net.

In main.c, since you did not declare that store_length returns a double,
the compiler will assume it returns an int.  It will then try to cast that
to a double, thereby rendering it undecipherable.

Modify main.c thusly:

#include <stdio.h>
double store_length (double);
main()
{double a,b;

  a = 1.234;
  b = store_length(a);
  printf("b=%f\n",b);
}

(Note to those who will warn me about the ANSI header:  it can be
 deduced from his file rt1.c that he is using a compiler which
 supports the prototypes.)