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 <string>
#include "MathUtil.h" bool MathUtil::isPrime(int number)
{
// ignore negative sign
number = abs(number); // 0 and 1 are no prime numbers
if (number == || number == ) {
return false;
} // find divisor that divides without a remainder
int divisor;
for (divisor = number / ; number%divisor != ; --divisor) {
;
} // if no divisor greater than 1 is found, it is a prime number
return divisor == ;
}
测试代码
PredicateTest.cpp
#include <list>
#include <algorithm>
#include <iostream>
#include "../../Algorithm/MathUtil.h"
#include "PredicateTest.h" using namespace std; void PredicateTest::unaryPredicate()
{
list<int> 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 ----------------