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From: jk@cs.man.ac.uk (John Kewley ICL)
Newsgroups: comp.lang.c++
Subject: function parameters
Message-ID: <2569@m1.cs.man.ac.uk>
Date: 24 May 91 13:24:19 GMT
Sender: news@cs.man.ac.uk
Reply-To: jk@cs.man.ac.uk (John Kewley ICL)
Organization: Department of Computer Science, University of Manchester UK
Lines: 39

The following program is supposed to print 81, the square of 9.
Unfortunately I would prefer to use a function which takes a constant
int pointer as a parameter to pass to g rather than a variable one.

This program fails to compile because of the const on the line labelled below.
//---------------------------------------------------------
#include <stdio.h>

typedef int int_fn( int* );

int g(const int_fn* fn, int i)
{
        return(fn(&i));
}

int f(const int* i)                // CC complains here
{
        return( *i**i );
}

int main()
{
        printf( "i=%d\n",g(f,9) );
        return(0);
}
//---------------------------------------------------------
Error message:
line 17: error: bad argument  1 type for g(): int (*)(const int *)
( int (*)(int *) expected)
//---------------------------------------------------------

Why is this, apart from "because the syntax is defined like that", why is 
a function with consts on its parameters not valid in place of one with
variable as parameters?
--
        J.K.
 
John M. Kewley, ICL, Wenlock Way, West Gorton, Manchester. M12 5DR
Tel:   (+44) 61 223 1301 X2138  Email: jk@cs.man.ac.uk / jk@nw.stl.stc.co.uk