project1st<Arg1, Arg2>

Category: functors Component type: type


Project1st is a function object that takes two arguments and returns its first argument; the second argument is unused. It is essentially a generalization of identity to the case of a Binary Function.


int main()
  vector<int> v1(10, 137);
  vector<char*> v2(10, (char*) 0);
  vector<int> result(10);

  transform(v1.begin(), v1.end(), v2.begin(), result.begin(),
            project1st<int, char*>());
  assert(equal(v1.begin(), v1.end(), result.begin()));


Defined in the standard header functional, and in the nonstandard backward-compatibility header function.h. This function object is an SGI extension; it is not part of the C++ standard.

Template parameters

Parameter Description Default
Arg1 project1st's first argument type, and its result type.  
Arg2 project1st's second argument type.  

Model of

Adaptable Binary Function

Type requirements


Public base classes

binary_function<Arg1, Arg2, Arg1>


Member Where defined Description
first_argument_type Adaptable Binary Function The type of project1st's first argument: Arg1
second_argument_type Adaptable Binary Function The type of project1st's second argument: Arg2
result_type Adaptable Binary Function The type of the result: Arg1.
Arg1 operator()(const Arg1& x, const Arg2&) const Adaptable Binary Function Function call. The return value is x.

New members

All of project1st's members are defined in the Adaptable Binary Function requirements. project1st does not introduce any new members.


See also

Function objects, identity, project2nd, select1st, select2nd
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