在C ++中使用fstream在文件中查找字符串

Question

這是我的代碼

/*
    Asks the user for their ID, depending on the ID depends on the results. It either goes to maintanance
    or it asks the user to return DVD's or check DVD's out and changes the stock of the DVD's.
    Cody Close
*/

#include <iostream>
#include <fstream>
#include <conio.h>
#include <sstream>
#include <string>

using namespace std;

void custID();
void sales();
void returns();
void discounts();
void maint();
void createAcc(string* filename, string* newID);
bool checkID(string* filename, string* search);

int main()
{
   //Declares all the variables for the program
   int mainID= 99959, menuChoice;
   bool close = false;
   bool done = false;
   string vidId;

   //Declares and input file and opens a file
   fstream inFile;
   inFile.open("dayin00.dat");

   do{
       do{
           cout << "accountID: " << endl;
           cin >> mainID;
           stringstream out;
           out << mainID;
           mainid = out.str();
           checkID("IDlist.txt", mainid);
       }while(mainid.length() < 5 || mainid.length() > 9);
           if(mainID!= 99959)
           {
               do
               {
                   cout << "MENU:" << endl;
                   cout << "(1)Purchase\n(2)Return\n(3)Exit" << endl;
                   cin >> menuChoice;
                   switch(menuChoice)
                   {
                   case 1:
                   case 2:
                   case 3:
                       done = true;
                   }
               }while(done == false);
           }else{
               maint();
           }

       close = true;
   }while(close == false);

   return 0;
}

void maint()
{
   int maintChoice;

   cout << "\n(1)Summary\n(2)Withdrawl\n(3)Close Down\n(4)Back to >main\n(0)Help" << endl;
   cin >> maintChoice;

   switch (maintChoice)
   {
       case 1:

       case 2:
       case 3:
       case 4:
       default:
           cout << "1 for summary, 2 for withdrawl, 3 to close down, 4 to >go back to main" << endl;
   }
}

void createAcc(string* filename, string* newID)
{
   fstream newFile;
   newFile.open(filename);
   newFile << newID;
}
void checkID(string* filename, string* ID)
{
   fstream infile;
   infile.open("IDlist.txt");
   string word;

   infile >> word;
   while (!infile.eof()){
       if(word == ID)
       {
           cout << "ID FOUND!" << endl;
       }else{
           createAcc(infile, ID);
       }
   }
}

文本文件僅包含ID99959。如何檢查用戶鍵入的ID是否已存在於文本文件中，如果不存在，則轉到createAcc（），使用該ID設置新帳戶用戶已輸入。

Answer 1

該代碼以讀取模式打開具有用戶ID的文件，逐行讀取它並嘗試查找ID。 如果在文件中找不到ID，它將以寫入模式打開文件，並在文件中添加用戶ID。

#include <iostream>
#include <fstream>
#include <stdexcept>

void createAcc(const std::string& filename, const std::string& id)
{
    std::ofstream os(filename);
    if (os)
        os << id;
    else
        throw std::runtime_error("Open file error: " + filename);
}

bool isStringContainsID(const std::string& line, const std::string& id)
{
    if (line.find(id) == std::string::npos)
        return false;
    else
        return true;
}

bool isFileContainsID(const std::string& filename, const std::string& id)
{
    std::ifstream is(filename);
    if (!is)
        throw std::runtime_error("Open file error: " + filename);
    std::string line;
    while (is) 
    {
         std::getline(is, line);
         if (isStringContainsID(line, id))
             return true;
    }
    return false;
}

int main() {

    std::string id("99959");
    std::string file_name("IDlist.txt");

    if (isFileContainsID(file_name, id))
        std::cout << "ID FOUND!" << std::endl;
    else
        createAcc(file_name, id);

    return 0;
}

請注意，所有用戶ID的字符串表示形式都應具有相同的長度，否則代碼可以在包含較大ID且文件ID較短的子字符串中找到較短的ID。