引用的向量不通过函数

Question

函数的引用向量不会将信息保存在内存中.我必须使用指针吗？

谢谢.

#include <iostream>
#include <cstdlib>
#include <vector>
#include <string>

using namespace std;

void menu();
void addvector(vector<string>& vec);
void subvector(vector<string>& vec);
void vectorsize(const vector<string>& vec);
void printvec(const vector<string>& vec);
void printvec_bw(const vector<string>& vec);

int main()
{
    vector<string> svector;

    menu();

    return 0;
}
//functions definitions

void menu()
{
    vector<string> svector;
    int choice = 0;

        cout << "Thanks for using this program! \n"
             << "Enter 1 to add a string to the vector \n"
             << "Enter 2 to remove the last string from the vector \n"
             << "Enter 3 to print the vector size \n"
             << "Enter 4 to print the contents of the vector \n"
             << "Enter 5 ----------------------------------- backwards \n"
             << "Enter 6 to end the program \n";
        cin >> choice;

        switch(choice)
        {

                case 1:
                    addvector(svector);
                    menu();
                    break;
                case 2:
                    subvector(svector);
                    menu();
                    break;
                case 3:
                    vectorsize(svector);
                    menu();
                    break;
                case 4:
                    printvec(svector);
                    menu();
                    break;
                case 5:
                    printvec_bw(svector);
                    menu();
                    break;
                case 6:
                    exit(1);
                default:
                    cout << "not a valid choice \n";

            // menu is structured so that all other functions are called from it.
        }

}

void addvector(vector<string>& vec)
{
    //string line;

     //int i = 0;
        //cin.ignore(1, '\n');
        //cout << "Enter the string please \n";
        //getline(cin, line);
        vec.push_back("the police man's beard is half-constructed");    

}

void subvector(vector<string>& vec)
{
    vec.pop_back();
    return;
}

void vectorsize(const vector<string>& vec)
{
    if (vec.empty())
    {
        cout << "vector is empty";
    }
    else
    {
        cout << vec.size() << endl;
    }
    return;
}

void printvec(const vector<string>& vec)
{
    for(int i = 0; i < vec.size(); i++)
    {
        cout << vec[i] << endl;
    }

    return;
}

void printvec_bw(const vector<string>& vec)
{
    for(int i = vec.size(); i > 0; i--)
    {
        cout << vec[i] << endl;
    }

    return;
}

Answer 1

你的问题是每次调用menu()都会创建一个隐藏前一个向量的新向量,这就是为什么你觉得它们似乎是空的.如果您真的想以递归方式调用菜单,请将您在main中创建的向量引用传递给它.

话虽如此,菜单系统很少会递归.您可能希望循环调用main中的menu()循环,直到用户选择退出为止.