Struct, Pointers a function creation

**SuperMiguel** · 06-27-2012

So im studying structs and i have a question about them

if you have something like this:

Code:

struct Person {
  int age;
  int SSN;
  int weight;
};

Then i want to make a function

Code:

struct Person *Person_make(int age, int SSN, int weight)
{
blah blah
}

Why do i have to use the pointer notation before the function name??

ie *Person_mane ???

**laserlight** · 06-27-2012

Originally Posted by SuperMiguel

Why do i have to use the pointer notation before the function name??

ie *Person_mane ???

Actually, the syntax is:

Code:

RETURN_TYPENAME Person_make(int age, int SSN, int weight)
{
    /* ... */
}

Where RETURN_TYPENAME is: struct Person *

**SuperMiguel** · 06-27-2012

So that function must return a pointer of type Person?

like Person *c = malloc(sizeof(*c));

return c;

**laserlight** · 06-27-2012

Yes (rather, struct Person, not Person, unless you have the appropriate typedef).

**SuperMiguel** · 06-27-2012

Originally Posted by laserlight

Yes (rather, struct Person, not Person, unless you have the appropriate typedef).

Yup, cool thanks

**SuperMiguel** · 06-27-2012

Well i have one more question...

If i use typedef.. for example:

Code:

 
Typedef struct {  int age;
  int SSN;
  int weight;
}Person;

i can do this: Person *test = malloc(sizeof(*test) ?? instead of with out typedef using struct Person *test = malloc(sizeof(struct Person)

Like on the 1st example i can pass the name of the pointer i just created instead of the struct name?

**whiteflags** · 06-27-2012

You can do sizeof(*test) no matter what the type of *test is, and it will always be correct.

The only reason to typedef a type is to create another name for that type, for aesthetic purposes.

**SuperMiguel** · 06-27-2012

thxs

**ledow** · 06-28-2012

If you typedef in that instance, it saves you having to keep typing struct. That's about the only advantage, but that can be a big one if you have a lot of these types floating about. I typedef structs by habit and only really type struct in the header files that define the typedef.

**grumpy** · 06-28-2012

Originally Posted by SuperMiguel

Then i want to make a function

Code:

struct Person *Person_make(int age, int SSN, int weight)
{
blah blah
}

Why do i have to use the pointer notation before the function name??

Actually, you don't have to.

It is possible to return a struct by value (rather than returning a pointer). That does rely on the compiler having visibility of the struct definition (as opposed to just a forward declaration) though.

Which is right? That depends on what you are trying to achieve. The two methods of returning a struct enable different things.

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