If I want to define a pointer variable p to point to the function foo() defined as below, what should be the exact type of p?
int *foo(void *arg)
{
...
}
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5 Answers
It should be
typedef int *(*funtion_foo_type)(void *);
4 Comments
Basile Starynkevitch
Actually, I would suggest that defining a
typedef for the function signature, that is like the function but with typedef before, e.g. typedef int*foo_type(void*); then using a pointer to that type, i.e. foo_type* funptr; is even more readable
Kyrylo Polezhaiev
However, this is not a type. This is a type definition operator.
too honest for this site
@KyryloPolezhaiev:
typedef is not an operator. Syntactically it is a storage-class specifier. A typedefed name is an alias for the actual type.Kyrylo Polezhaiev
Sorry, I meant statement. I didn't mean
typedef, I meant whole string. Tried to avoid confusion, made more confusion (:You need to have the pointer as the pointer to a function, returning an int *, accepting a void* argument. You can make it like
int * (*p) (void *);
and then, you can use
p = foo;
Comments
Bearing in mind the comment of Kyrylo Polezhaiev, the type of p is
int*(*)(void*)
To declare p, you need to insert the name at the correct point in the type:
int*(*p)(void*);
but it is generally more readable to use an alias:
typedef int*(func_t)(void*);
func_t* p;
Comments
To make it more easy you could for the function declaration
int *foo(void *arg);
define an alias named as for example Tfoo that looks the same way as the function declaration itself
typedef int *Tfoo(void *);
After that to declare a function pointer to the function is very easy. Just write
Tfoo *foo_ptr = foo;
Otherwise you could write
typedef int * (* TFoo_ptr )(void *);
Tfoo_ptr foo_ptr = foo;
Or you could write a declaration of the function pointer directly without using the typedef/
int * (* foo_ptr )(void *) = foo;
answered Jan 21, 2016 at 20:11
Vlad from Moscow
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Comments
Are you talking about pointer to function?
First define a pointer to function that takes void argumenta and return int
typedef int (*Ptrtofun)(void);
Now safely can point this to your function.
Ptrtofun p;
p = &foo(void);
Now you have a ptr p to function and can easily use it ..
