CPP

c++ bind what are placeholders

// C++ code to demonstrate bind() and
// placeholders
#include <iostream>
#include <functional> // for bind()
using namespace std;
  
// for placeholders
using namespace std::placeholders;
  
// Driver function to demonstrate bind()
void func(int a, int b, int c)
{
    cout << (a - b - c) << endl;
}
  
int main()
{
    // for placeholders
    using namespace std::placeholders;
  
    // Use of bind() to bind the function
    // _1 is for first parameter and assigned
    // to 'a' in above declaration.
    // 2 is assigned to b
    // 3 is assigned to c
    auto fn1 =  bind(func, _1, 2, 3);
  
    // 2 is assigned to a.
    // _1 is for first parameter and assigned
    // to 'b' in above declaration.
    // 3 is assigned to c.
    auto fn2 =  bind(func, 2, _1, 3);
  
    // calling of modified functions
    fn1(10);
    fn2(10);
  
    return 0;
}