boost库使用—函数回调

boost库使用—函数回调

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result_of

确定表达式的类型

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包含头文件：

#include <boost/utility/result_of.hpp>

using namespace boost;

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案例：

#include <iostream>
#include <boost/utility/result_of.hpp>
using namespace std;

int main()
{
	typedef double(*Func)(double);
	Func func = sqrt;
	result_of<Func(double)>::type x = func(5.0);
	cout << "type:"<<typeid(x).name() << endl;
	

	system("pause");
	return 0;
}

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ref 和 cref

boost.ref 应用代理模式，引入对象包装器的概念；函数对象作为参数时使用较多；降低了复制的代价

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包含头文件：

#include <boost/ref.hpp>

using namespace boost;

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原型：

ref:  boost::reference_wrapper<T> ref(T& t);
cref: boost::reference_wrapper<T> ref(T const& t);

ref 用于包装按引用传递的值。
cref 用于包装按const引用传递的值。

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#include <iostream>
#include <boost/ref.hpp>

using namespace std;

void test(int &n)
{
	n = n + 10;
	cout << "n:"<<n << endl;//20
}

int main()
{
	int n = 10;
	test(ref(n));
	cout << "n:" << n << endl;//20
	system("pause");
	return 0;
}

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bind + function

关于两种说明在微信公众号：CPP后台服务器开发 中有，欢迎参观

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bind + function + ref

案例：

#include <iostream>
#include "boost/bind.hpp"
#include "boost/ref.hpp"
#include <boost/function.hpp>

struct A
{
	A(int aValue) : m_value(aValue)
	{
		std::cout << "A()" << std::endl;
		m_value = 10;
	}

	A(const A& a)
	{
		std::cout << "A(const A&)" << std::endl;
		this->m_value = a.m_value;
	}

	int m_value;
};

void f(A a)
{
	std::cout << "f(A)" << std::endl;
}

void g(A& a)
{
	std::cout << "g(A&)" << std::endl;
}

void test(int x,int y)
{
	std::cout << "x:" << x << std::endl;
	std::cout << "y:"<< y << std::endl;
}
typedef boost::function<void(void)>Func;
typedef boost::function<void(int)>Func2;
int main()
{
	A a(10);

	std::cout << "...f1..." << std::endl;
	boost::bind(&f, a)();
	std::cout << "...f2..." << std::endl;
	boost::bind(&f, boost::ref(a))();

	std::cout << "...g1..." << std::endl;
	boost::bind(&g, a)();
	std::cout << "...g2..." << std::endl;
	boost::bind(&g, boost::ref(a))();
	Func F(boost::bind(&g, boost::ref(a)));
	F();
	int x = 2,y =5;
	Func F2(boost::bind(&test, boost::ref(x), boost::ref(y)));
	F2();
	system("pause");
	return 0;
}

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