Thread: Function pointers syntax and excercise.

This is from C++ Primer 5th edition excercise 6.54 and 6.55.

So the first excercise goes like this:
Write a declaration for a function that takes two int parameters and returns an int, and declare a vector whose elements have this function pointer type.

I believe I managed to do the first excercise, but I am not sure since the next exercise, which I dont have a clue what to do with, is a followup on the first excercise.

Code:

using PF = int(*)(int*, int);

    vector<PF> ivec;

This is how I declared my vector, I have some doubt whether this is correct or not..

The next exercise:
Write four functions that add, subtract, multiply, and divide two int values. Store pointers to these values in your vector from the previous exercise.

Writing the functions are E-Z-P-Z lemon squeezy, but the next part in storing pointers to these values in the vector is killing me.

I think part of the problem is that I maybe have an incorrect type for the vector. I have tried to just declare pointers to each function, and use each pointer in the vector, but then I think I had to set the type for the vector to int, which I believe is wrong?

Anyway, any help is much appreciated.

Originally Posted by Iceboxes

So the first excercise goes like this:
Write a declaration for a function that takes two int parameters and returns an int, and declare a vector whose elements have this function pointer type.

I believe I managed to do the first excercise, but I am not sure since the next exercise, which I dont have a clue what to do with, is a followup on the first excercise.

Code:

using PF = int(*)(int*, int);
 
    vector<PF> ivec;

This is how I declared my vector, I have some doubt whether this is correct or not..

Well, why not write a program to check? For example, if what you wrote is correct, I would expect this program to compile and output 5 when run:

Code:

#include <iostream>
#include <vector>

int foo(int a, int b)
{
    return a + b;
}

int main()
{
    using namespace std;

    using PF = int(*)(int*, int);

    vector<PF> ivec;

    ivec.push_back(foo);
    cout << ivec[0](2, 3) << endl;
}

Thanks guys! It compiled and I think it is working as it should.

@laserlight, part of my problem (which I didnt mention) was that I didnt know exactly what to do in order to add the functions to my vector.. Didnt know it was as easy as to use push_back. I tried direct initialization and stuff like that. (Never really compiled, but that is prolly because I just derp at syntax often)

Anyways, just using push_back to add the functions to the vector, the program is working as it should! Thank you very much!

@tabstop, MY function is taking int and int... I posted a direct copy of how they did it in the book, but in my program I wrote int and int. >,< So sorry >.>

Direct initialization...

Code:

int add(int a, int b) { return 0; }
int sub(int a, int b) { return 0; }
int mul(int a, int b) { return 0; }
int mydiv(int a, int b) { return 0; }

int main()
{
	using FPtr_t = int(*)(int, int);
	std::vector<FPtr_t> MyFunc{ &add, &sub, &mul, &mydiv };
}