Can you help me with typedef?

brownstone · 06-11-2004, 06:19 AM

hi

You can use typedef to create new data type names.But I'm wondering why we need typedef if you can use #define instead?Or is there something #define can't do but typedef can?

thank you

nimra · 06-11-2004, 07:25 AM

I might missed something, but I think you can't create data structures with define. The define just make a substitution.

As an example:

typedef struct {
double x;
double y;
} myType;

myType a,b;

Two instances are created (also memory is allocated therefore). I think doing something like this is not possible with define.

crazyduck · 06-11-2004, 07:43 AM

Code:

#define smyType struct myType
 struct myType {
        double x;
        double y;
} ;

int main(void)
{
 smyType a,b;
 printf("it works :D \n");
}
~                                                                               
~

it works too, and it not require typedef

...but if the question is not "why we need typedef if you can use #define instead", but "why we need #define to define new types if you can use typedef instead?"

an the answer for YOUR question is:
* cos it's more easy to understand code wuthout too many #define's
* cos if you will migrate to c++ later your project can support namespaces with typedef (#define not)
* with #define it's quite easy to make mistake praticly not to solve by debug...
* and so on...

and now what about my question("why we need #define...")?

worldmagic · 06-11-2004, 10:09 AM

I actually thought the compiler could check typedefs, but not defines (due to that its a preprocessor macro). however I tested this with GCC by defining and typedefing two types (original int) and then I sent them as arguments to a function taking int. And GCC did not complain about either! ..