[nzlug] C expert advise wanted

[Eliot Blennerhassett]

Raimund Eimann wrote:
> Hi,
> 
> a C program I'm currently writing uses two very similar structs, say struct_a 
> and struct_b.
> 
> struct struct_a {
> 	var a;
> 	var b;
> 	struct struct_a *next;	
> }
> 
> struct struct_b {
> 	var a;
> 	var b;
> 	struct struct_a *c;	
> 	struct struct_b *next;
> }
> 
> In order to process these structs, I've got two functions proc_a() and 
> proc_b(). Both function only operate on the (simple) variables a and b which 
> exist in both struct and are of the same type.

It doesn't look like it. Each function mallocs a different struct...


> int proc_a(var *c, struct struct_a **a) {
> 	struct struct_a *dummy = malloc(...);
> 	
> 	dummy->a = ...
> 	dummy->b = ...
> 	...
> 	*a = dummy;
> }
> 
> int proc_b(var *c, struct struct_b **b) {
> 	struct struct_b *dummy = malloc(...);
> 	
> 	dummy->a = ...
> 	dummy->b = ...
> 	...
> 	*b = dummy;
> }
> 
> Is there some way of avoiding this code repetition and only have a single 
> function which is capable of processing both types of structs?

Factor out the common parts...

struct common {
	var a;
	var b;
}

struct struct_a {
	struct common c;
	etc..
}

struct struct_b {
	struct common c;
	etc..
}

int proc_common ( struct common * c)
{
	c->a = ....;
	c->b = ... ;
}

int proc_a( )
{
	struct struct_a dummy;
	proc_common(&dummy->common);
}

int proc_b( )
{
	struct struct_ dummy;
	proc_common(&dummy->common);
}

> NZLUG mailing list NZLUG at linux.net.nz
> http://www.linux.net.nz/cgi-bin/mailman/listinfo/nzlug