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# std::bind1st, std::bind2nd

From cppreference.com
< cpp‎ | utility‎ | functional

Defined in header `<functional>` |  |
template< class F, class T > std::binder1st<F> bind1st( const F& f, const T& x ); | (1) | (until C++17) (deprecated since C++11)
template< class F, class T > std::binder2nd<F> bind2nd( const F& f, const T& x ); | (2) | (until C++17) (deprecated since C++11)

Binds a given argument `x` to a first or second parameter of the given binary function object `f`. That is, stores `x` within the resulting wrapper, which, if called, passes `x` as the first or the second parameter of `f`.

1) Binds the first argument of `f` to `x`. Effectively calls std::binder1st<F>(f, typename F::first_argument_type(x)).

2) Binds the second argument of `f` to `x`. Effectively calls std::binder2nd<F>(f, typename F::second_argument_type(x)).

### [edit] Parameters

f | - | pointer to a function to bind an argument to
x | - | argument to bind to `f`

### [edit] Return value

A function object wrapping `f` and `x`.

### [edit] Exceptions

(none)

### [edit] Example

Run this code

    #include <iostream>
    #include <algorithm>
    #include <functional>
    #include <cmath>
    #include <vector>

    int main()
    {
        std::vector<double> a= {0, 30, 45, 60, 90, 180};
        std::vector<double> r(a.size());
        double pi = std::acos(-1);

        std::transform(a.begin(), a.end(), r.begin(),
            std::bind1st(std::multiplies<double>(), pi / 180.));
    // equivalent lambda: [pi](double a){ return a*pi/180.; });

        for(size_t n = 0; n < a.size(); ++n)
            std::cout << a[n] << " deg = " << r[n] << " rad\n";
    }

Output:

    0 deg = 0 rad
    30 deg = 0.523599 rad
    45 deg = 0.785398 rad
    60 deg = 1.0472 rad
    90 deg = 1.5708 rad
    180 deg = 3.14159 rad

### [edit] See also

binder1stbinder2nd (until C++17)(until C++17) | function object holding a binary function and one of its arguments (class template) [edit]

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