Christian Ivicevic Christian Ivicevic - 1 month ago 9
C++ Question

Using generic std::function objects with member functions in one class

For one class I want to store some function pointers to member functions of the same class in one

map
storing
std::function
objects. But I fail right at the beginning with this code:

class Foo {
public:
void doSomething() {}
void bindFunction() {
// ERROR
std::function<void(void)> f = &Foo::doSomething;
}
};


I receive
error C2064: term does not evaluate to a function taking 0 arguments
in
xxcallobj
combined with some weird template instantiation errors. Currently I am working on Windows 8 with Visual Studio 2010/2011 and on Win 7 with VS10 it fails too. The error must be based on some weird C++ rules i do not follow.

EDIT: I do NOT use boost. This is C++11 integrated in the MS compiler.

Answer

A non-static member function must be called with an object. That is, it always implicitly passes "this" pointer as its argument.

Because your std::function signature specifies that your function doesn't take any arguments (<void(void)>), you must bind the first (and the only) argument.

std::function<void(void)> f = std::bind(&Foo::doSomething, this);

If you want to bind a function with parameters, you need to specify placeholders:

using namespace std::placeholders;
std::function<void(int,int)> f = std::bind(&Foo::doSomethingArgs, this, _1, _2);

Or, if your compiler supports C++11 lambdas:

std::function<void(int,int)> f = [=](int a, int b) {
    this->doSomethingArgs(a, b);
}

(I don't have a C++11 capable compiler at hand right now, so I can't check this one.)

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