STL实践（count_if）

 

vs2003编译器对count_if的实现格式与规范中例子不一样。

count_if的第3个参数输入是一个函数对象，应该是一个返回bool值的函数。在下例中构造了一个类，重载了

bool operator() (string& SalesRecord) ，值得注意。

引用自http://stl.winterxy.com/html/000013.html

#include  < iostream >
#include  < string >
#include  < list >
#include  < algorithm >

using   namespace  std;


class  IsAToothbrush 
... {
public:
  IsAToothbrush(string& InToothbrushCode) : 
      ToothbrushCode(InToothbrushCode) ...{}
  bool operator() (string& SalesRecord) 
  ...{
    return SalesRecord.substr(0,4)==ToothbrushCode;
  }       
private:
  string ToothbrushCode;        
} ;

int  main ( void ) 
... {
    list<string> SalesRecords;

    SalesRecords.push_back("0001 Soap");
    SalesRecords.push_back("0002 Shampoo");
    SalesRecords.push_back("0003 Toothbrush");
    SalesRecords.push_back("0004 Toothpaste");
    SalesRecords.push_back("0003 Toothbrush");

    string VariableToothbrushCode("0003");

    int NumberOfToothbrushes(0);  
    NumberOfToothbrushes  = count_if (SalesRecords.begin(), SalesRecords.end(), 
        IsAToothbrush(VariableToothbrushCode));


    cout << "There were  "
        << NumberOfToothbrushes 
        << " toothbrushes matching code "
        << VariableToothbrushCode
        << " sold" 
        << endl;
}