How to assign function pointer to a function

Question

I have this program and I'm getting:

lvalue required as left operand of assignment

because of the line function_a = function.

int function_a(int j){
    return j+10;
}

int function_b(int j){
    return j;
}

void set_a(int (*function)(int)){
    function_a = function;
}

int main(){
    int a = function_a(2);
    printf("%d, ", a);

    set_a(function_b);

    int b = function_a(2);
    printf("%d", b);
}

I want to set function_a to function_b in function set_a. So I'm expecting output 12, 2. What I should do to assign this properly?

What have you done so far in attempting to solve your problem? — Manav Dubey
– Manav Dubey, Commented Apr 4, 2017 at 22:00

Stephan Lechner · Accepted Answer · 2017-04-04 22:09:53Z

7

A function definition cannot be replaced by assignment, i.e. a function definition is not an lvalue to which you can assign something, and that's why you get the error; But you can define a function pointer and assign different function definitions, and call the function pointer just as if it were a function in the sense of an ordinary function definition:

int function_a(int j){
    return j+10;
}

int function_b(int j){
    return j;
}

int (*f)(int) = function_a;

void set_a(int (*function)(int)){
    f = function;
}


int main(int argc, const char *argv[])
{

    int a = f(2);
    printf("%d, ", a);

    set_a(function_b);

    int b = f(2);
    printf("%d", b);

    return 0;
}

answered Apr 4, 2017 at 22:09

Stephan Lechner

35.2k4 gold badges38 silver badges59 bronze badges

Sign up to request clarification or add additional context in comments.

Collectives™ on Stack Overflow

How to assign function pointer to a function

1 Answer 1

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Related