not1,not2,bind1st and bind2nd detailed

1. Introduction

The bind1st and bind2nd functions are used to convert a two-dollar operator (binary FUNCTOR,BF) into a unary operator (unary Functor,uf). To achieve this, they require two parameters: the BF to be converted and a value (v).

Perhaps this explanation after the people are not very clear, then speak a little vernacular it. The expressions we write when we do comparisons are like x > K, x < K, where k is a parameter indicating that the expression in your program is to be compared with the K value. The above two expressions correspond to the bind2nd, the simple understanding is that the K as the second parameter of the comparison expression. If you use bind1st, the corresponding expression is k > X,k < X, that is, K is the first parameter of a comparison expression. You may notice that there is no comparison in this, but don't worry about it, you will see how to achieve the comparison. Let's take two examples to see the usage of bind1st and bind2nd.

• f = std::bind1st (functor, v); ' F (x) ' is equivalent to ' functor (V, x) '
• f = std::bind2nd (functor, v); ' F (x) ' is equivalent to ' functor (x, v) '

2.bind1st and bind2nd examples

int a[] = {12};std::vectorint4) ; // remove all elements less than 100 arr.erase (std::remove_if (Arr.begin (),  int)), Arr.end ());

The comparison expression here is equivalent to Arr.value < 100, and if you use bind1st it means the opposite.

// remove all elements greater than 100 arr.erase (std::remove_if (Arr.begin (),  int)), Arr.end ());

The expression here is equivalent to < Arr.value, but in order to delete elements greater than 100 you can also use bind2nd

// remove all elements greater than 100 arr.erase (std::remove_if (Arr.begin (),  int)), Arr.end ());

Before said = comparison, for example x <= K How to achieve it, STD also provides a good thing not1, we can say! (x > K) and x <= K are equivalent, let's look at the following expression:

// remove all elements less than or equal to 100 arr.erase (std::remove_if (Arr.begin (),  int)), Arr.end ());

3. Description

not1 is a negation of the return value is a single-purpose function , STD also has Not2 it is negative return value is the function of the binocular

3.1 not1 Example

1 //NOT1 Example2#include <iostream>//Std::cout3#include <functional>//std::not14#include <algorithm>//std::count_if5 6 structisodd {7   BOOL operator() (Const int& x)Const{returnX%2==1;}8typedefintArgument_type;9 };Ten  One intMain () { A   intValues[] = {1,2,3,4,5}; -   intCX = std::count_if (values, values+5, Std::not1 (IsOdd ())); -Std::cout <<"there is"<< CX <<"elements with even values.\n"; the   return 0; -}

View Code3.2 Not2 Example

1 //Not2 Example2#include <iostream>//Std::cout3#include <functional>//Std::not2, Std::equal_to4#include <algorithm>//Std::mismatch5#include <utility>//std::p air6 7 intMain () {8   intFoo[] = {Ten, -, -, +, -};9   intBar[] = {0, the, -, $, -};Tenstd::p air<int*,int*>Firstmatch,firstmismatch; OneFirstmismatch = Std::mismatch (foo, foo+5, Bar, std::equal_to<int>()); AFirstmatch = Std::mismatch (foo, foo+5, Bar, Std::not2 (std::equal_to<int>())); -Std::cout <<"First mismatch in bar are"<< *firstmismatch.second <<'\ n'; -Std::cout <<"First match in Bar is"<< *firstmatch.second <<'\ n'; the   return 0; -}

View Code

Examples need to include header files

#include <vector>

#include <algorithm>

#include <functional>

not1,not2,bind1st and bind2nd detailed