A helper template function that creates an adaptor to convert a binary function object into a unary function object by binding the first argument of the binary function to a specified value.

The binary function object to be converted to a unary function object.

_Left

The value to which the first argument of the binary function object is to be bound.

Return Value

The unary function object that results from binding the first argument of the binary function object to the value _Left.

Remarks

Function binders are a kind of function adaptor and, because they return function objects, can be used in certain types of function composition to construct more complicated and powerful expressions.

If _Func is an object of type Operation and c is a constant , then bind1st ( _Func, c ) is equivalent to the binder1st class constructor binder1st<Operation> ( _Func, c ) and is more convenient.

// functional_bind1st.cpp
// compile with: /EHsc
#include <vector>
#include <functional>
#include <algorithm>
#include <iostream>
using namespace std;
// Creation of a user-defined function object
// that inherits from the unary_function base class
class greaterthan5: unary_function<int, bool>
{
public:
result_type operator( ) ( argument_type i )
{
return (result_type) (i > 5);
}
};
int main( )
{
vector <int> v1;
vector <int>::iterator Iter;
int i;
for ( i = 0 ; i <= 5 ; i++ )
{
v1.push_back( 5 * i );
}
cout << "The vector v1 = ( " ;
for ( Iter = v1.begin( ) ; Iter != v1.end( ) ; Iter++ )
cout << *Iter << " ";
cout << ")" << endl;
// Count the number of integers > 10 in the vector
int result1a;
result1a = count_if( v1.begin( ), v1.end( ), bind1st( less<int>( ), 10 ) );
cout << "The number of elements in v1 greater than 10 is: "
<< result1a << "." << endl;
// Compare: counting the number of integers > 15 in the vector
// with a user defined function object
int result1b;
result1b = count_if( v1.begin( ), v1.end( ), greaterthan5( ) );
cout << "The number of elements in v1 greater than 15 is: "
<< result1b << "." << endl;
// Count the number of integers < 10 in the vector
int result2;
result2 = count_if( v1.begin( ), v1.end( ), bind2nd( less<int>( ), 10 ) );
cout << "The number of elements in v1 less than 10 is: "
<< result2 << "." << endl;
}

The vector v1 = ( 0 5 10 15 20 25 )
The number of elements in v1 greater than 10 is: 3.
The number of elements in v1 greater than 15 is: 4.
The number of elements in v1 less than 10 is: 2.