Thread: passing a function as an argument

hi,
I am trying to write a function that gets an outputstream, a schedule(which is just a list pointers to items), and a function.
this function should be performed on each item in the schedule, and if it returns true it should print out the item.

Code:

std::ostream& printfilteredschedule(std::ostream& os, const Schedule& s, bool condition(const ScheduleItem*))
{   for (Schedule::const_iterator i = s.begin(); i != s.end(); ++i)
        if (condition(*i))
            (*i)->print(os);
    return os;
}

// somewhere else in code

bool filteralarm(const FancyScheduleItem* si)
{   ulint t(time(0));
    return (si->getbegin() >= t && std::min(si->getbegin() - (60 * si->getalarm()), (ulint)0) <= t);
}

// again somewhere else in the code

else if (showtype == "ALARM")
    {   printfilteredschedule(std::cout, s, filteralarm);
    }

when I try to compile with this code it give me the following errors:
58 D:\school\struII\taak3\processcommands.cc [Warning] the address of `bool filteralarm(const FancyScheduleItem*)', will always evaluate as `true'

[Linker error] undefined reference to `printfilteredschedule(std:stream&, Schedule const&, bool)'

I hope somebody can explain me what I am doing wrong.

thanks a lot

in this code condition is supposed to be a function

Then why did you declare it a bool type:

bool condition

You need to pass a pointer to a function as an argument to printfilteredschedule(). Here is an example of the syntax:

Code:

#include <iostream>
#include <string>
using namespace std;


int func(double d, string str)
{
	cout<<d<<endl;
	cout<<str<<endl;

	return 10;
}

void doSomething(double num, int(*funcPointer)(double, string) )
{
	cout<<num<<endl;

	funcPointer(12.5, "hello world");
}

int main() {

	int(*pfunc)(double, string) = func;
	
	doSomething(100.5, pfunc);
	
	return 0;
}

Why would you need to pass a function as an argument? They're declared globally.

EDIT: Looking at 7stud's example, I don't quite see why anyone would need to do that. Looks pretty interesting though.

Originally Posted by SlyMaelstrom

Why would you need to pass a function as an argument? They're declared globally.

EDIT: Looking at 7stud's example, I don't quite see why anyone would need to do that. Looks pretty interesting though.

any number of reasons. You might want to write a callback function or you might not want to have a header dependency for a start.

Look at boost.bind and std::for_each.

and change your fricking sig! it's damn annoying!