Question

I have a function that requires a function pointer as argument:

int func(int a, int (*b)(int, int))
{
    return b(a,1);
}

Now I want to use a certain function that has three arguments in this function:

int c(int, int, int)
{
    // ...
}

How can I bind the first argument of c so that I’m able to do:

int i = func(10, c_bound);

I’ve been looking at std::bind1st but I cannot seem to figure it out. It doesn’t return a function pointer right? I have full freedom to adapt func so any changes of approach are possible. Althoug I would like for the user of my code to be able to define their own c…

note that the above is a ferocious simplification of the actual functions I’m using.

The project sadly requires C++98.

Answer 1

You can’t do that. You would have to modify func to take a function-object first. Something like:

int func( int a, std::function< int(int, int) > b )
{
    return b( a, rand() );
}

In fact, there is no need for b to be an std::function, it could be templated instead:

template< typename T >
int func( int a, T b )
{
    return b( a, rand() );
}

but I would stick with the std::function version for clarity and somewhat less convoluted compiler output on errors.

Then you would be able to do something like:

int i = func( 10, std::bind( &c, _1, _2, some-value ) );

Note all this is C++11, but you can do it in C++03 using Boost.