Predicate是一种特殊的辅助函数，它会返回Boolean，常常被用来作为排序或者查找准则。

Predicate会有1个或者2个操作数。

 

Unary Predicate(单参判断式)

例子：

我们先写一个算法，如下：

MathUtil.h

#ifndef _Math_Util_H_#define _Math_Util_H_using namespace std;class MathUtil{public:    static bool isPrime(int number);};#endif

 

MathUtil.cpp

#include 
     
      #include "MathUtil.h"bool MathUtil::isPrime(int number){    // ignore negative sign    number = abs(number);    // 0 and 1 are no prime numbers    if (number == 0 || number == 1) {        return false;    }    // find divisor that divides without a remainder    int divisor;    for (divisor = number / 2; number%divisor != 0; --divisor) {        ;    }    // if no divisor greater than 1 is found, it is a prime number    return divisor == 1;}
     

测试代码

PredicateTest.cpp

#include 
     
      #include 
      
       #include 
       
        #include "../../Algorithm/MathUtil.h"#include "PredicateTest.h"using namespace std;void PredicateTest::unaryPredicate(){    list
        
          coll;    int startNumber, endNumber;    cout << "Input Start Number: " << endl;    cin >> startNumber;    cout << "Input End Number: " << endl;    cin >> endNumber;    // insert elements from start number to end number    for (int i = startNumber; i <= endNumber; ++i) {        coll.push_back(i);    }    // search for prime number    auto pos = find_if(coll.cbegin(), coll.cend(),  // range        MathUtil::isPrime);                    // predicate    if (pos != coll.end()) {        // found        cout << *pos << " is first prime number found" << endl;    }    else {        // not found        cout << "no prime number found" << endl;    }}void PredicateTest::run(){    printStart("unaryPredicate()");    unaryPredicate();    printEnd("unaryPredicate()");}
        
       
      
     

 

运行结果：

---------------- unaryPredicate(): Run Start ----------------

Input Start Number:

30

Input End Number:

50

31 is first prime number found

---------------- unaryPredicate(): Run End ----------------