如何使用 std::transform(） 函数

How to use std::transform() function

本文关键字：函数 transform std 何使用      更新时间：2023-10-16

好吧，基本上我需要使用 std：：transform(( 函数。但是，我正在尝试将对象函数作为最后一个参数传入，但它似乎不起作用。

class isprime {
  public:
    // declares the constructor and the operator() overloading
    isprime(){ number = 0, primes.push_back(2);};
    bool operator()(int);
  private:
    // various private functions and variables
   int number;
   list<int> primes;    //creats a list via the stl library
   void morePrimes(int);    //function to generate more prime numbers
   bool it; // Iterator for the morePrimes list
   bool primeCheck;         // Bool used in the morePrimes function
};

bool isprime::operator()(int number)
{
    if(number == 1)             //returns false for 1
        return false;
    if(number > primes.back()){     //Tests to see if the list of primes range would include the number, if not it runs the morePrimes function
        morePrimes(number);
    }
    it = binary_search(primes.begin(),primes.end(),number); //uses stl find to see if the number is in the list of primes.
    if(it)  //if the returned iterator points to a value = to number then number is prim.
        return true;
    return false;       //returns false if the number wasnt found
};
 transform(random_list.begin(), random_list.end(), isprime_list.begin(), test());

上面我包含了我用于转换的类、函数和调用。有人知道为什么这不起作用吗？我想不通。

如果您在某处提供void isprime::more_primes(int)，则删除test()中的括号可能就足够了：

int main()
{
    auto gen = bind(uniform_int_distribution<>(), mt19937());
    list<int> random_list;
    for (int i=0; i<5; i++) random_list.push_back(gen());
    list<int> isprime_list(random_list.size());
    isprime test;
    transform(random_list.begin(), random_list.end(), isprime_list.begin(), test);
}

在 Coliru 上看到它"运行"(好吧，编译(：http://coliru.stacked-crooked.com/a/3d908cb5cdc5c543

#include <list>
#include <algorithm>
using namespace std;
class isprime {
    public:
        // declares the constructor and the operator() overloading
        isprime(){ number = 0, primes.push_back(2);};
        bool operator()(int);
    private:
        // various private functions and variables
        int number;
        list<int> primes;     // creats a list via the stl library
        void morePrimes(int); // function to generate more prime numbers
        bool it;              // Iterator for the morePrimes list
        bool primeCheck;      // Bool used in the morePrimes function
};
bool isprime::operator()(int number)
{
    if(number == 1)              // returns false for 1
        return false;
    if(number > primes.back()){ // Tests to see if the list of primes range would include the number, if not it runs the morePrimes function
        morePrimes(number);
    }
    it = binary_search(primes.begin(),primes.end(),number); // uses stl find to see if the number is in the list of primes.
    if(it)                      // if the returned iterator points to a value = to number then number is prim.
        return true;
    return false;               // returns false if the number wasnt found
}
void isprime::morePrimes(int) {}
#include <random>
#include <functional>
#include <iostream>
#include <iterator>
int main()
{
    auto gen = bind(uniform_int_distribution<>(), mt19937());
    list<int> random_list;
    for (int i=0; i<5; i++) random_list.push_back(gen());
    list<int> isprime_list(random_list.size());
    isprime test;
    transform(random_list.begin(), random_list.end(), isprime_list.begin(), test);
}
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