Help me to understand strange 'typedef ... ' in some source... Post: 302983612

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Top Forums Programming Help me to understand strange 'typedef ... ' in some source... Post 302983612 by jim mcnamara on Thursday 13th of October 2016 09:51:09 PM

10-13-2016

Registered User

That is a typedef of a function. In this case the need was for portability -windows compiler versus maybe a linux C compiler.
No dataype declaration for the function. So, by default, the function will compile probably with a warning as a function that returns an integer.

So you do not worry about the platform, you will notice void * arguments. This lets you call COMPARE_ADDR with any datatypes as long as those datatypes are by reference (address of the object). It does not have a datatype for the function return. This kind of function typedef is usually done for situations where you want to call something to get a standard result, but windows and linux (example platform) do not have the same name for the function, but it may return { <0, 0, >0} for less than, equal to, or greater than.

Pretend example

Code:

#ifdef WIN32 
   COMPARE_ADDR=isequal;
#else
   COMPARE_ADDR=addr_foo;
#endif
/* see if the memory location of two variables is the same */
if  ( ! COMPARE_ADDR( &variable3, &variable1) {  /* if equal barf */
    errno=EINVAL;  /* invalid value error code */
    perror("Cannot continue, variables are identical and must not be identical\n");
    exit(1);   /* end program here */
}

Last edited by jim mcnamara; 10-13-2016 at 11:00 PM..

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LEARN ABOUT REDHAT

strange

XScreenSaver(1) 					      General Commands Manual						   XScreenSaver(1)

NAME

       strange - draws strange attractors

SYNOPSIS

       strange	[-display  host:display.screen]  [-foreground  color]  [-background  color]  [-window] [-root] [-mono] [-install] [-visual visual]
       [-ncolors integer] [-delay microseconds]

DESCRIPTION

       The strange program draws strange attractors

OPTIONS

       strange accepts the following options:

       -window Draw on a newly-created window.	This is the default.

       -root   Draw on the root window.

       -mono   If on a color display, pretend we're on a monochrome display.

       -install
	       Install a private colormap for the window.

       -visual visual
	       Specify which visual to use.  Legal values are the name of a visual class, or the id number (decimal or hex) of a specific visual.

       -ncolors integer
	       How many colors should be used (if possible).  Default 64.  The colors are chosen randomly.

ENVIRONMENT

       DISPLAY to get the default host and display number.

       XENVIRONMENT
	       to get the name of a resource file that overrides the global resources stored in the RESOURCE_MANAGER property.

SEE ALSO

       X(1), xscreensaver(1), xlock(1)

COPYRIGHT

       Copyright (C) 1997 by Massimino Pascal.

       Permission to use, copy, modify, and distribute this software and its documentation for any purpose and without fee is hereby granted, pro-
       vided  that  the  above copyright notice appear in all copies and that both that copyright notice and this permission notice appear in sup-
       porting documentation.

AUTHOR

       Massimino Pascal <Pascal.Massimon@ens.fr>, 1997.

       Ability to run standalone or with xscreensaver added by Jamie Zawinski <jwz@jwz.org>, 10-May-97.

X Version 11							     10-May-97							   XScreenSaver(1)