How to Check if the function exists in C/C++

Question

Certain situations in my code, i end up invoking the function only if that function is defined, or else i should not. How can i achieve this ?

like:
if (func         


        

Answer 1

So another way, if you're using c++11 would be to use functors:

You'll need to put this at the start of your file:

#include 

The type of a functor is declared in this format:

std::function< return_type (param1_type, param2_type) >

You could add a variable that holds a functor for sum like this:

std::function&)> sum;

To make things easy, let shorten the param type:

using Numbers = const std::vectorn&;

Then you could fill in the functor var with any one of:

A lambda:

sum = [](Numbers x) { return std::accumulate(x.cbegin(), x.cend(), 0); } // std::accumulate comes from #include 

A function pointer:

int myFunc(Numbers nums) {
    int result = 0;
    for (int i : nums)
        result += i;
    return result;
}
sum = &myFunc;

Something that 'bind' has created:

struct Adder {
    int startNumber = 6;
    int doAdding(Numbers nums) {
        int result = 0;
        for (int i : nums)
            result += i;
        return result;
    }
};
...
Adder myAdder{2}; // Make an adder that starts at two
sum = std::bind(&Adder::doAdding, myAdder);

Then finally to use it, it's a simple if statement:

if (sum)
    return sum(x);

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In summary, functors are the new pointer to a function, however they're more versatile. May actually be inlined if the compiler is sure enough, but generally are the same as a function pointer.

When combined with std::bind and lambda's they're quite superior to old style C function pointers.

But remember they work in c++11 and above environments. (Not in C or C++03).