Windows apps
Collapse the table of content
Expand the table of content
Information
The topic you requested is included in another documentation set. For convenience, it's displayed below. Choose Switch to see the topic in its original location.

is_placeholder Class

 

The new home for Visual Studio documentation is Visual Studio 2017 Documentation on docs.microsoft.com.

The latest version of this topic can be found at is_placeholder Class.

Tests if type is a placeholder.

struct is_placeholder {
static const int value;
};

The constant value value is 0 if the type Ty is not a placeholder; otherwise, its value is the position of the function call argument that it binds to. You use it to determine the value N for the Nth placeholder _N.

// std_tr1__functional__is_placeholder.cpp   
// compile with: /EHsc   
#include <functional>   
#include <iostream>   
  
using namespace std::placeholders;   
  
template<class Expr>   
    void test_for_placeholder(const Expr&)   
    {   
    std::cout << std::is_placeholder<Expr>::value << std::endl;   
    }   
  
int main()   
    {   
    test_for_placeholder(3.0);   
    test_for_placeholder(_3);   
  
    return (0);   
    }  
  

0  
3  

Header: <functional>

Namespace: std

_1 Object

Show:
© 2017 Microsoft