编程序实现以下功能: (1) 按职工号由小到大的顺序将5个员工的数据(包括号码、姓名、年龄、工资)输出到磁盘文件中保存。 (2) 从键盘输入两个员工的数据(职工号大于已有的职工号)，增加到文件的末尾。 (3) 输出文件中全部职工的数据。 (4) 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，就输出“无此人”。可以反复多次查询，如果输入查找的职工号为0，就结束查询。

下面是一个实现以上功能的C++程序：

#include <iostream>
#include <fstream>
#include <string>
#include <algorithm>
using namespace std;

struct Employee {
    int id;
    string name;
    int age;
    double salary;
};

bool cmp(Employee a, Employee b) {
    return a.id < b.id;
}

void saveToFile(Employee employees[], int n, string filename) {
    ofstream ofs(filename, ios::out);
    if (!ofs) {
        cerr << "Failed to open file for writing!" << endl;
        return;
    }
    sort(employees, employees + n, cmp);
    for (int i = 0; i < n; i++) {
        ofs << employees[i].id << " "
            << employees[i].name << " "
            << employees[i].age << " "
            << employees[i].salary << endl;
    }
    ofs.close();
}

Employee readFromKeyboard() {
    Employee employee;
    cout << "Input id, name, age, salary: ";
    cin >> employee.id >> employee.name >> employee.age >> employee.salary;
    return employee;
}

void appendToFile(Employee employee, string filename) {
    ofstream ofs(filename, ios::app);
    if (!ofs) {
        cerr << "Failed to open file for appending!" << endl;
        return;
    }
    ofs << employee.id << " "
        << employee.name << " "
        << employee.age << " "
        << employee.salary << endl;
    ofs.close();
}

void displayAll(string filename) {
    ifstream ifs(filename, ios::in);
    if (!ifs) {
        cerr << "Failed to open file for reading!" << endl;
        return;
    }
    int count = 0;
    Employee employee;
    while (ifs >> employee.id >> employee.name >> employee.age >> employee.salary) {
        cout << employee.id << " "
            << employee.name << " "
            << employee.age << " "
            << employee.salary << endl;
        count++;
    }
    ifs.close();
    if (count == 0) {
        cout << "No employees found!" << endl;
    }
}

void searchById(string filename) {
    ifstream ifs(filename, ios::in);
    if (!ifs) {
        cerr << "Failed to open file for reading!" << endl;
        return;
    }
    int id;
    bool found = false;
    Employee employee;
    cout << "Input id to search (0 to exit): ";
    cin >> id;
    while (id != 0) {
        int count = 0;
        found = false;
        ifs.seekg(0, ios::beg);
        while (ifs >> employee.id >> employee.name >> employee.age >> employee.salary) {
            count++;
            if (employee.id == id) {
                found = true;
                cout << "Employee #" << count << ": " << endl
                    << "id: " << employee.id << " "
                    << "name: " << employee.name << " "
                    << "age: " << employee.age << " "
                    << "salary: " << employee.salary << endl;
                break;
            }
        }
        if (!found) {
            cout << "No employee with id " << id << " found!" << endl;
        }
        cout << "Input id to search (0 to exit): ";
        cin >> id;
    }
    ifs.close();
}

int main() {
    const int MAX_EMPLOYEES = 5;
    string filename = "employees.txt";
    Employee employees[MAX_EMPLOYEES] = {
        {103, "Tom", 30, 5000.0},
        {101, "Jerry", 28, 4500.0},
        {104, "Alice", 35, 8000.0},
        {105, "Bob", 32, 6000.0},
        {102, "Marry", 26, 4000.0}
    };
    int n = MAX_EMPLOYEES;
    saveToFile(employees, n, filename);
    cout << "Saved " << n << " employees to file " << filename << endl;

    Employee employee1 = readFromKeyboard();
    appendToFile(employee1, filename);
    cout << "Appended 1 employee to file " << filename << endl;

    Employee employee2 = readFromKeyboard();
    appendToFile(employee2, filename);
    cout << "Appended 1 employee to file " << filename << endl;

    displayAll(filename);

    searchById(filename);

    return 0;
}

在这个程序中，我们定义了一个结构体Employee，包含职工号码、姓名、年龄和工资等信息。程序中使用了STL库中的ofstream、ifstream、sort等函数来实现文件的读写和数据的排序等操作。

程序中首先将5个员工的数据保存到文件中，然后从键盘输入两个员工的数据，并将它们追加到文件末尾。接着输出文件中全部职工的数据，最后实现了按职工号从文件中查找职工的功能。

注意，在处理文件时，我们需要对文件是否成功打开进行检查，避免文件操作失败导致程序崩溃。此外，我们在读写文件时使用了文件流的seekg函数来实现文件的随机读取，这样可以快速定位到文件中指定位置的数据。