Making a function to choose an interface depending on arguments

Question

I want to make a function to choose another one in C, maybe this C-pseudo code can help a little to clarify what I want:

void set_method(const char *method)
{
    // Check if the method is serial_port
    if (strcmp(method, "serial_port") == 0)
    {
        // assign the alias "print" to serial_print
        // something like defing here a function like this:
        // print(const char *print) { serial_print(print); }

        print(const char *print) = serial_print(const char *message)
    } 
    else if (strcmp(method, "graphical_tty") == 0)
    {
        // The same that serial_port case but with graphical_tty_print
    } 
    else
    {
        // Error
    } 
} 

The goal is to assign an "alias" to a function if the condition is met, how can I do this?

I'm using a freestanding C implementation for this, compiled with clang.

Answer 1

It seems as you are looking for function pointers. See the following code, which introduces a type of function to call, a global pointer to a function of that type, and the code assigning an appropriate function according to your logic:

typedef int (*PrintFunctionType)(const char*);

int serial_print(const char *message) { printf("in serial: %s\n", message); return 0; }
int tty_print(const char* message) { printf("in tty: %s\n", message); return 0; }


PrintFunctionType print = serial_print;  // default

void set_method(const char *method)
{
    // Check if the method is serial_port
    if (strcmp(method, "serial_port") == 0)        {
        print  = serial_print;
    }
    else if (strcmp(method, "graphical_tty") == 0)        {
        print = tty_print;
    }
    else       {
        // Error
    }
}

int main() {
    print("Hello!");
    set_method("graphical_tty");
    print("Hello!");
}

//Output:
//
//in serial: Hello!
//in tty: Hello!

Hope it helps :-)