How to use boost bind with a member function - c++

Question

The following code causes cl.exe to crash (MS VS2005).
I am trying to use boost bind to create a function to a calls a method of myclass:
#include "stdafx.h"
#include <boost/function.hpp>
#include <boost/bind.hpp>
#include <functional>
class myclass {
public:
void fun1() { printf("fun1()\n"); }
void fun2(int i) { printf("fun2(%d)\n", i); }
void testit() {
boost::function<void ()> f1( boost::bind( &myclass::fun1, this ) );
boost::function<void (int)> f2( boost::bind( &myclass::fun2, this ) ); //fails
f1();
f2(111);
}
};
int main(int argc, char* argv[]) {
myclass mc;
mc.testit();
return 0;
}
What am I doing wrong?

Answer 1

Use the following instead:
boost::function<void (int)> f2( boost::bind( &myclass::fun2, this, _1 ) );
This forwards the first parameter passed to the function object to the function using place-holders - you have to tell Boost.Bind how to handle the parameters. With your expression it would try to interpret it as a member function taking no arguments.
See e.g. here or here for common usage patterns.
Note that VC8s cl.exe regularly crashes on Boost.Bind misuses - if in doubt use a test-case with gcc and you will probably get good hints like the template parameters Bind-internals were instantiated with if you read through the output.

Answer 2

Boost.Bind is a library that simplifies and generalizes capabilities that originally required std::bind1st() and std::bind2nd()
Example 1.1: std::for_each() with a compatible function
#include <vector>
#include <algorithm>
#include <iostream>
void print(int i)
{
std::cout << i << '\n';
}
int main()
{
std::vector<int> v{1, 3, 2};
std::for_each(v.begin(), v.end(), print);
}
The third parameter of std::for_each() is a function or function object that expects a sole parameter. In Example 1.1, std::for_each() passes the numbers in the container v as sole parameters, one after another, to print().
If you need to pass in a function whose signature doesn’t meet the requirements of an algorithm, it gets more difficult. For example, if you want print() to accept an output stream as an additional parameter, you can no longer use it as is with std::for_each().
Example 1.2. std::for_each() with std::bind1st()
#include <vector>
#include <algorithm>
#include <functional>
#include <iostream>
class print : public std::binary_function<std::ostream*, int, void>
{
public:
void operator()(std::ostream *os, int i) const
{
*os << i << '\n';
}
};
int main()
{
std::vector<int> v{1, 3, 2};
std::for_each(v.begin(), v.end(), std::bind1st(print{}, &std::cout));
}
Like Example 1.1, Example 1.2 writes all numbers in v to standard output. However, this time, the output stream is passed to print() as a parameter. To do this, the function print() is defined as a function object derived from std::binary_function.
With Boost.Bind, you don’t need to transform print() from a function to a function object. Instead, you use the function template boost::bind(), which is defined in boost/bind.hpp.
Example 1.3: std::for_each() with boost::bind()
#include <boost/bind.hpp>
#include <vector>
#include <algorithm>
#include <iostream>
void print(std::ostream *os, int i)
{
*os << i << '\n';
}
int main()
{
std::vector<int> v{1, 3, 2};
std::for_each(v.begin(), v.end(), boost::bind(print, &std::cout, _1));
}
Example 1.3 uses print() as a function, not as a function object. Because print() expects two parameters, the function can’t be passed directly to std::for_each(). Instead, boost::bind() is passed to std::for_each() and print() is passed as the first parameter to boost::bind().
Since print() expects two parameters, those two parameters must also be passed to boost::bind(). They are a pointer to std::cout and _1.
_1 is a placeholder. Boost.Bind defines placeholders from _1 to _9. These placeholders tell boost::bind() to return a function object that expects as many parameters as the placeholder with the greatest number. If, as in Example 1.3, only the placeholder _1 is used, boost::bind() returns a unary function object – a function object that expects a sole parameter. This is required in this case since std::for_each() passes only one parameter.
std::for_each() calls a unary function object. The value passed to the function object – a number from the container v – takes the position of the placeholder _1. boost::bind() takes the number and the pointer to std::cout and forwards them to print().
Please note that boost::bind(), like std::bind1st() and std::bind2nd(), takes parameters by value. To prevent the calling program from trying to copy std::cout, print() expects a pointer to a stream. Boost.Ref provides a function which allows you to pass a parameter by reference.
Example 1.4 illustrates how to define a binary function object with boost::bind(). It uses the algorithm std::sort(), which expects a binary function as its third parameter.
Example 1.4. std::sort() with boost::bind()
#include <boost/bind.hpp>
#include <vector>
#include <algorithm>
#include <iostream>
bool compare(int i, int j)
{
return i > j;
}
int main()
{
std::vector<int> v{1, 3, 2};
std::sort(v.begin(), v.end(), boost::bind(compare, _1, _2));
for (int i : v)
std::cout << i << '\n';
}
In Example 1.4, a binary function object is created because the placeholder _2 is used. The algorithm std::sort() calls this binary function object with two values from the container v and evaluates the return value to sort the container. The function compare() is defined to sort v in descending order.
Since compare() is a binary function, it can be passed to std::sort() directly. However, it can still make sense to use boost::bind() because it lets you change the order of the parameters. For example, you can use boost::bind() if you want to sort the container in ascending order but don’t want to change compare()
Example 1.5. std::sort() with boost::bind() and changed order of placeholders
#include <boost/bind.hpp>
#include <vector>
#include <algorithm>
#include <iostream>
bool compare(int i, int j)
{
return i > j;
}
int main()
{
std::vector<int> v{1, 3, 2};
std::sort(v.begin(), v.end(), boost::bind(compare, _2, _1));
for (int i : v)
std::cout << i << '\n';
}

Answer 3

The following works for me.
class test_component
{
private:
void on_wait_complete(const int i);
};
void test_component::on_wait_complete (const int i)
{
cout << "on_wait_complete was called" << endl;
return;
}
int main()
{
// timerPtr_ is a variable declared in class test_component.
timerPtr_->async_wait(boost::bind(&test_component::on_wait_complete, this, _1));
}