1. 预定义函数对象

C++标准库内含许多预定义的函数对象，也就是内置的函数对象。

你可以充分利用他们，不必自己费心去写一些自己的函数对象。

要使用他们，你只要包含如下头文件

#include <functional>

eg:

set<int, less<int>> coll;  // sort elements with <

set<int, greater<int>> coll;  // sort elements with >

predefinedFuncObjectTest.cpp

deque
     
       coll = { 1, 2, 3, 5, 7, 11, 13, 17, 19 };PRINT_ELEMENTS(coll, "initialized: ");// negate all values in colltransform(coll.cbegin(), coll.cend(),      // source    coll.begin(),                   // destination    negate
      
       ());                 // operationPRINT_ELEMENTS(coll, "negated:     ");// square all values in colltransform(coll.cbegin(), coll.cend(),      // first source    coll.cbegin(),                  // second source    coll.begin(),                   // destination    multiplies
       
        ());             // operationPRINT_ELEMENTS(coll, "squared:     ");
       
      
     

运行结果:

---------------- predefinedFuncObject(): Run Start ----------------

initialized: 1 2 3 5 7 11 13 17 19

negated:     -1 -2 -3 -5 -7 -11 -13 -17 -19

squared:     1 4 9 25 49 121 169 289 361

---------------- predefinedFuncObject(): Run End ----------------

 

2. 预定义函数对象绑定

你可以使用binder将预定义函数对象和其他数值进行绑定。

pdFuncObjectBind.cpp

using namespace std::placeholders;set
     

> coll1 = { 1, 2, 3, 4, 5, 6, 7, 8, 9 };deque

coll2;// Note: due to the sorting criterion greater<>() elements have reverse order:PRINT_ELEMENTS(coll1, "initialized: ");// transform all elements into coll2 by multiplying them with 10transform(coll1.cbegin(), coll1.cend(), // source back_inserter(coll2), // destination bind(multiplies

(), _1, 10)); // operationPRINT_ELEMENTS(coll2, "transformed: ");// replace value equal to 70 with 42replace_if(coll2.begin(), coll2.end(), // range bind(equal_to

(), _1, 70), // replace criterion 42); // new valuePRINT_ELEMENTS(coll2, "replaced: ");// remove all elements with values between 50 and 80coll2.erase(remove_if(coll2.begin(), coll2.end(), bind(logical_and

(), bind(greater_equal

(), _1, 50), bind(less_equal

(), _1, 80))), coll2.end());PRINT_ELEMENTS(coll2, "removed: ");