C++ function pointers

Elio發表於2019-05-10
C++Function

Function pointers point to the address of the executable code of the function. You can use pointers to call functions and to pass functions as arguments to other functions.

Syntax

Declaration

A simple example:

void (*foo) (int)

A function pointer foo is declared in the above code, which can point to a function with an integer as argument and no return. It`s as if you`re declaring a function called *foo, which takes an int and returns void; now, if *foo is a function, then foo must be a pointer to a function. (Similarly, a declaration like int *x can be read as *x is an int, so x must be a pointer to an int.)

The key to writing the declaration for a function pointer is that you`re just writing out the declaration of a function but with (*func_name) where you`d normally just put func_name.

Initialization

To initialize a function pointer, you must give it the address of a function in your program.

void print(int x){
    printf( "%d
", x );
}

int main(){
    // 1. declaration + initialization
    void (*foo)(int) = & print; 
    // 2. declaration; initialization
    void (*foo_2)(int);
    foo_2 = & print;
    // 3. typedef
    typedef void(*printInt)(int);
    printInt foo_3 = & print;
    return 0;
}

Méthode d`usage

The function pointer is similar to the array. where a bare array decays to a pointer, but you may also prefix the array with & to request its address.

foo(2);
(*foo)(10);

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