std::bind,std::cref的简单使用

#include 
#include 
#include 
 
void f(int n1, int n2, int n3, const int& n4, int n5)
{
    std::cout << n1 << ' ' << n2 << ' ' << n3 << ' ' << n4 << ' ' << n5 << '\n';
}
 
int g(int n1)
{
    return n1;
}
 
struct Foo {
    void print_sum(int n1, int n2)
    {
        std::cout << n1+n2 << '\n';
    }
    int data = 10;
};
 
int main()
{

    //占位符，来记录参数的位置

    using namespace std::placeholders; //for _1, _2, _3...
 
    // demonstrates argument reordering and pass-by-reference
    int n = 7;

    //std::cref是按址传递，其他是按值传递，_2是第二个参数

    auto f1 = std::bind(f, _2, _1, 42, std::cref(n), n);
    n = 10;
    f1(1, 2, 1001); // 1 is bound by _1, 2 is bound by _2, 1001 is unused
 
    // nested bind subexpressions share the placeholders
    auto f2 = std::bind(f, _3, std::bind(g, _3), _3, 4, 5);
    f2(10, 11, 12);
 
    // common use case: binding a RNG with a distribution

   //很简单的生成0-10的随机数

    std::default_random_engine e;
    std::uniform_int_distribution<> d(0, 10);
    std::function<int()> rnd = std::bind(d, e);
    for(int n=0; n<10; ++n)
        std::cout << rnd() << ' ';
    std::cout << '\n';
 
    // bind to a member function
    Foo foo;
    auto f3 = std::bind(&Foo::print_sum, foo, 95, _1);
    f3(5);
 
    // bind to member data
    auto f4 = std::bind(&Foo::data, _1);
    std::cout << f4(foo) << '\n';
}

Output:

2 1 42 10 7
12 12 12 4 5
1 5 0 2 0 8 2 2 10 8
100
10