c++ - 当要读取的文件已经打开时，文件读取进入无限循环

Question

我写这段代码是为了制作日记或日记。它接受输入，对其进行加密并将其存储在名为“yourDiary.txt”的文件中。当要求解密时，它要求输入密码(当前为“pwd”)。如果密码匹配，它会将“yourDiary.txt”解密为“yourDiaryDecrypted.txt”。它通常工作正常。但是，如果在文本编辑器中打开“yourDiary.txt”，程序就会进入无限循环，“yourDiaryDecrypted.txt”会无限增长。有人请告诉原因。

我找不到问题的根源，所以上传了整个代码。

    // writing on a text file
#include <iostream>
#include <ctime>
#include <fstream>
using namespace std;


string encryptDecrypt(string toEncrypt) {                       //encryption,decryption function
    char key = 'K'; //Any char will work
    string output = toEncrypt;

    for (int i = 0; i < toEncrypt.size(); i++)
        output[i] = toEncrypt[i] ^ key;

    return output;
}
int main () {
  int mode;cout<<"Enter 1 to add new entry, 0 to see the diary\n"; cin>>mode;
  ofstream f ("yourDiary.txt",ios::app);
  time_t now=time(0);
  char *ltm=ctime(&now);
  string line,line2,pwd;
  string encrypted = encryptDecrypt(ltm);                       //timestamp encrypted and added to file
  string decrypted;
  f<<encryptDecrypt("**");                              //to find end of file
  f<<"\n\n\n\n";
  f << encrypted << "\n\n";
  if(mode==1){
    cout<<"speak your heart out. when you feel better enter **++**\n";
    for(;;){
        getline(cin,line);
        if(line=="**++**"){
            encrypted=encryptDecrypt(line);
            f << encrypted <<"\n";
            break;                                  //end cuurrent data entry
        }
        else{
            encrypted=encryptDecrypt(line);
            f << encrypted <<"\n";                          //line to file
        }
    }
    f.close();
  }
  if (mode==0){
    cout<<"enter password\n"; 
    cin.ignore();
    getline(cin,pwd);
    if(pwd=="pwd"){                                 //encryption of password
        ofstream dia("yourDiaryDecrypted.txt",ios::trunc);
        fstream f("yourDiary.txt");
      NEXT: getline(f,line);
        decrypted=encryptDecrypt(line);
        if (decrypted!="**++**"){
            dia<<decrypted<<"\n";
            goto NEXT;                                  //restart loop
        }
        else{
            getline(f,line2);
            decrypted=encryptDecrypt(line2);
            if(decrypted=="**"){
                dia<<decrypted<<"\n";
                goto NEXT;                              //restart loop
            }
            else{
                goto EXIT;                              //break loop
            }
        }
      EXIT: dia.close();f.close();
        cout<<"You can now see your decrypted diary\n  :)\n";
    }
    else{
        cout<<"wait for the password. I will give it to you in due time\n";
    }
  }
  cout<<"press enter to continue";
  cin.ignore();
  return 0;
}

谢谢。

Answer 1

我相信问题不在您的代码中，而是在您运行它并输入数据时。当它以模式 == 1 询问时，我运行了你的代码
cout<<"speak your heart out. when you feel better enter **++**\n";
如果你不输入 **++**当你用它制作 yourDiary.txt 时，它会因此进入无限循环

NEXT: getline(f,line);
    decrypted=encryptDecrypt(line);
    if (decrypted!="**++**"){
        dia<<decrypted<<"\n";
        goto NEXT;

它永远找不到**++**如果你不输入它，它就会一直循环。当我输入 **++** 时它起作用了或者您可以按照评论中的建议使用 while 循环而不是 goto。这需要在 if(mode == 1)

 f<<encryptDecrypt("**"); 
 f<<"\n\n\n\n";
 f << encrypted << "\n\n";

否则，如果您运行 mode == 0，它将在 yourdiary.txt 中打印此内容，如果您再次运行 mode == 0，则会导致无限循环。