C++编程实现以下功能： 1、定义职工类employee：字段成员：职工号num，姓名name，年龄age，工资salary； 成员函数：返回职工号getnum()；友元函数：重载运算符>>，<<。 2、编写函数按职工号从小到大的顺序将 5 个职工的数据输出到磁盘文件 file1.txt中保存，int savetofile()；该函数返回输入数据的个数。 3、编写函数从键盘输入一个员工的数据，增加到文件file1.txt 的末尾，int insertfile(int n)；插入完成后将新的员工的数量返回。 4、编写函数从文件中输出全部员工的数据，void outfromfile(int n)。 5、编写函数从键盘输入一个号码，从文件中查找有无此职工号，如有则显示此职工是第几个职工以及此职工的全部数据，如没有，输出“无此人”，void findfile(int n)。

以下是实现以上功能的代码：

#include <iostream>
#include <fstream>
#include <string>
#include <algorithm>

using namespace std;

class employee {
private:
    int num;
    string name;
    int age;
    int salary;

public:
    employee(int n = 0, string nm = "", int a = 0, int s = 0) : num(n), name(nm), age(a), salary(s) {}

    int getnum() const {
        return num;
    }

    friend istream& operator>>(istream& is, employee& e) {
        is >> e.num >> e.name >> e.age >> e.salary;
        return is;
    }

    friend ostream& operator<<(ostream& os, const employee& e) {
        os << e.num << "\t" << e.name << "\t" << e.age << "\t" << e.salary << endl;
        return os;
    }

    bool operator<(const employee& e) const {
        return num < e.num;
    }
};

int savetofile(employee arr[], int n) {
    sort(arr, arr+n); // 按职工号从小到大排序
    ofstream ofs("file1.txt");
    if (!ofs) {
        cerr << "Failed to open file1.txt" << endl;
        return 0;
    }
    for (int i = 0; i < n; i++) {
        ofs << arr[i];
    }
    ofs.close();
    return n;
}

int insertfile() {
    ifstream ifs("file1.txt");
    if (!ifs) {
        cerr << "Failed to open file1.txt" << endl;
        return 0;
    }
    int n = 0;
    employee e;
    while (ifs >> e) {
        n++;
    }
    ifs.close();

    ofstream ofs("file1.txt", ios::app);
    if (!ofs) {
        cerr << "Failed to open file1.txt" << endl;
        return 0;
    }
    cout << "Enter data for the new employee (num name age salary): ";
    cin >> e;
    ofs << e;
    ofs.close();
    return n+1;
}

void outfromfile(int n) {
    ifstream ifs("file1.txt");
    if (!ifs) {
        cerr << "Failed to open file1.txt" << endl;
        return;
    }
    employee e;
    for (int i = 0; i < n; i++) {
        if (!(ifs >> e)) {
            cerr << "Failed to read from file1.txt" << endl;
            ifs.close();
            return;
        }
        cout << e;
    }
    ifs.close();
}

void findfile(int n) {
    ifstream ifs("file1.txt");
    if (!ifs) {
        cerr << "Failed to open file1.txt" << endl;
        return;
    }
    employee e;
    int i = 0;
    while (ifs >> e) {
        i++;
        if (e.getnum() == n) {
            cout << "This employee is the " << i << "th employee." << endl;
            cout << e;
            ifs.close();
            return;
        }
    }
    cout << "No such employee." << endl;
    ifs.close();
}

int main() {
    employee arr[5] = {
        employee(2, "Tom", 25, 3500),
        employee(3, "Jerry", 30, 4500),
        employee(1, "Alice", 20, 2500),
        employee(4, "Bob", 35, 5500),
        employee(5, "David", 40, 6500)
    };

    int n = savetofile(arr, 5);
    cout << "Saved " << n << " employees to file1.txt" << endl;

    n = insertfile();
    cout << "Inserted a new employee. Now there are " << n << " employees in file1.txt" << endl;

    cout << "All employees in file1.txt: " << endl;
    outfromfile(n);

    int num;
    cout << "Enter a number to search: ";
    cin >> num;
    findfile(num);

    return 0;
}

这里使用了文件流来读写文件，并且重载了运算符>>和<<来方便地输入输出职工数据。插入新员工时使用了文件流的ios::app模式来在文件末尾添加数据。