Does anyone know anything about functions that return pointers to functions?

Suppose I want a function that takes an integer argument and returns a
pointer to a function that takes a string argument.  I discovered on my own,
after about thirty minutes of trial and error, that I could use a prototype
like the one below:

    double (*foo (int a)) (char *c);

where foo is the function that returns a pointer to the string-valued
function, where the referenced function returns a double.  The caller would
be as follows:

    foo (integer_argument) (string_argument);

I wrote some code to test something like this.  I got it working just fine
on a UNIX box and an MS-DOS box.  This program has no particular use, it
just demonstrates what I'm talking about.  What I am asking is this: does
anyone know whether or not this standard ANSI C?

----------------------------------------------------------- cut here --------
#include <stdio.h>

/*  You can put prototypes here if you want to.  */

double four (char *c) {
    printf ("integer argument is four; string is \"%s\"\n",c);
    return 4.0;
    }

double two (char *c) {
    printf ("integer argument is two; string is \"%s\"\n",c);
    return 2.0;
    }

double not_two_or_four (char *c) {
    printf ("integer argument is not two or four; string is \"%s\"\n",c);
    return 0.0;
    }

/*
 *  In this example, foo takes an integer argument and returns a
 *  pointer to a string-valued function.  The referenced string-valued
 *  function returns a double.
 */

double (*foo (int a)) (char *c)
    {
    if (a==4)
        return four;
    else if (a==2)
        return two;
    else
        return not_two_or_four;
    }

void main (void)
    {
    int a;
    char str[30];
    double (*fp)(char *c);
    double z;

    while ( scanf("%d %s",&a,str) == 2 ) /* read integer argument and
                                            string argument */
        {
        fp = foo(a);     /* pointer to int-valued function */
        (*fp)(str);      /* execute that function */

        z = foo(a)(str); /* this demonstrates the caller and also
                            uses the return value of the function
                            returned by foo. */

        printf ("Return value is: %20g\n",z);
        }
    }
----------------------------------------------------------- cut here --------

--
#!/bin/ksh

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\(.\)/"$s"/g"|sed "s/^\(.*\)$/"$s"/g"|sed "s/\(.\)"`echo $s|sed "s/"'\\'$o"$//\
g"`"/"$o"/g"|sed "s/^\(.*\)"`echo $s|sed "s/"'\\'$o"$//g"`"$/"$o"/g"

    declare foo as function(int) returning pointer to function(pointer to char) returning double

and cdecl says to me:

    double (*foo(int ))(char *)

Hope this helps.
--

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3M Center, Bldg. 235-3B-16      fax:    (612) 737-2700

The easy way to define functions returning pointers to functions etc is
to to it in easy stages with typedef.

eg

    typedef char *foo(struct *really_big srb); // or even more complex

    typedef foo *baar(int i);    // Function returning pointer to ....

It's three years or so since I did this so please don't flame me for any
stupid mistakes in above. It should give you the idea, it works for any
complicated decl.

--
Regards

Alec Clews