Corrupted struct?

xconspirisist · 12-19-2004, 07:03 AM

Using C, writing it in Linux, Compiling with GCC. I'm having a wierd problem with structs. The structs are defined in public.h, data is written to them in main.c, but comes out very odd when read in public.c.

output

Code:

debug level: 134515272
debug level: 0.000000
port: -18390300
debug level: 2532503
debug level: 0.000000
port: 2866320
debug level: 2532503
debug level: 0.000000
port: 2866320
debug level: 2532503
debug level: 0.000000
port: 2866320

inc/public.h

Code:

*** 

struct options_t {
	int debug;
};

struct arguments_t
{
  char *args[2];            
  int port;            
};

***

src/main.c

Code:

int main (int argc, char **argv)
{	
	struct arguments_t s_arguments;
	struct options_t s_options;

	// set defaults
	s_arguments.port = 0;
	s_options.debug = 1;
	
	printf("%i\n", s_options.debug);
	
	debug("Parsing command line arguments...\n");
			
	argp_parse (&argp, argc, argv, 0, 0, &s_arguments);
	
	return 0;
}

src/public.c

Code:

void error ( const char *error_message ) {

	printf("\nERROR: %s \n\n", error_message );
	exit(0);
	
}

void debug ( const char *debug_message ) {
	struct options_t s_options;
	struct arguments_t s_arguments;
		
	printf("debug level: %i\n", s_options.debug);
	printf("debug level: %f\n", s_options.debug);
	printf("port: %i\n", s_arguments.port);
	
	if (s_options.debug == 1)
		printf("\nDEBUG: %s\n", debug_message );

}

Any help is greatly appreciated. Many thanks.

Dark_Helmet · 12-19-2004, 07:47 AM

As far as I can tell, you're not doing what you intend to do.

In the debug() function, you declare new structures, but never initialize them to anything. So that's why junk gets printed. The structures you modified in main() are not global, and you don't pass them to your function.

The structure definitions themselves (in public.h) are global, but when delaring a variable of that type, they exist only within a specific scope (even if the variables have the same names as other declarations).

xconspirisist · 12-19-2004, 07:59 AM

Many thanks for the help. I fixed it in the end

Dark_Helmet · 12-19-2004, 08:58 AM

Here's the thing, global variables are bad. That is, general guidelines for "good" programming practice discourage creating global variables unless there is no other alternative. The more accepted method is to pass variables by value or by reference. And that just means adding one (or more) arguments to your functions depending on how you want to use those arguments inside the function.

It's been a long time since I looked for tutorials, but I just went to google and plugged "C tutorial variable scope" in and got a lot of hits. One of them was the GNU C Programming Tutorial. It looks promising, but I can't vouch for it