Question

我想尝试对登录/注册程序进行编码。使用外部.txt文件作为数据库，我想在其中保留“注册”用户和密码。问题：我真的不能测试用户名的重复

    // Currently stuck here
    //Issue is that the if statment is not testing the way i want it to (comparing the usernames)

    //The .txt file that i am using contains the content: "Usernames: "

    //getline(myfile,line) returns "Usernames:" which is not really finding if there are any duplicates of usernames


    ifstream myfile(filename.c_str());

    while(getline(myfile,line)){

            cout<< line;

            if(line.find("Username: " + userregtry) == string::npos){

                    myfile.close();

                    ofstream writein(filename.c_str(),ios::app);

                    writein<< "Username: " << userregtry << "\n" ;
            }
            else{

                    cout<< "\nThis username has been taken\nPlease try another username: ";
            }
    }

Answer 1

假设每行有一个名字

有几个问题：

如果名称不在第一行，则认为该名称不存在，然后关闭文件，停止搜索
如果第一行中存在该名称，则警告您，然后继续；如果第二行中没有该名称的先验，则您认为该名称不存在
如果文件为空，它将保持为空

您需要查看所有行，然后才能考虑该名称不存在。

解决方案：

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

int main()
{
  string filename = "/tmp/foo";
  string userregtry;

  cout << "\nPlease enter username: ";

  for (;;) {
    if (!(cin >> userregtry))
      break;

    ifstream myfile(filename.c_str());
    bool found = false;
    string line;

    while (getline(myfile,line)) {
      if (line.find("Username: " + userregtry) != string::npos) {
        found = true;
        break;
      }
    }

    myfile.close();

    if (found)
      cout<< "\nThis username has been taken\nPlease try another username: ";
    else {
      ofstream writein(filename.c_str(),ios::app);
      writein<< "Username: " << userregtry << "\n" ;
      break;
    }
  }

  return 0;
}

从空文件执行：

/tmp % ./a.out
Please enter username: aze
/tmp % ./a.out
Please enter username: aze
This username has been taken
Please try another username: qsd
/tmp % ./a.out
Please enter username: qsd
This username has been taken
Please try another username: aze
This username has been taken
Please try another username: iop
/tmp % cat foo
Username: aze
Username: qsd
Username: iop

假设文件包含一行Usernames: name1 name2 ... namen

有几个问题：

您的代码没有找到名称，除非它位于第一个位置
添加新名称时，所有其他名称都会丢失
用户名或用户名 s 吗？

不终止唯一行的解决方案：

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

int main()
{
  string filename = "/tmp/foo";
  string line;

  {
    ifstream myfile(filename.c_str());

    if (getline(myfile,line))
      line += ' '; // to have a space before and after each name including the last
  }

  string userregtry;

  cout << "Please enter username: ";

  for (;;) {
    if (!(cin >> userregtry))
      return 0;

    if (line.find(' ' + userregtry + ' ') != string::npos)
      cout << "This username has been taken\nPlease try another username: ";
    else {
      ofstream writein(filename.c_str(),ios::app);

      if (line.empty())
        writein << "Usernames: ";
      else
        writein << ' ';

      writein << userregtry;
      return 0;
    }
  }
}

从空文件执行：

Please enter username: aze
/tmp % ./a.out
Please enter username: aze
This username has been taken
Please try another username: qsd
/tmp % ./a.out
Please enter username: aze
This username has been taken
Please try another username: qsd
This username has been taken
Please try another username: wxc
/tmp % cat foo ; echo "#"
Usernames: aze qsd wxc#

测试.txt文件中的重复用户名

1 个答案: