用C++重写一个文本文件

Question

使用一个处理文件流的程序。我想编辑存储在文本文件中的一行文本。根据我的理解，最好的方法是从原始文件中复制所有内容并将其覆盖在一个新文件中，并在编辑过程中进行编辑。我一直无法在网上找到一个清晰的例子，并想知道我能否看到一个例子。

例如文本文件包含：

user1 pass1 55 

user2 pass2 56 

user3 pass3 57 

我想编辑对地方有：

user1 pass1 55 

user2 pass2 44 

user3 pass3 57 

这里是我的情况下删节代码：

#include <iostream> 
#include <fstream> 

using namespace std; 
//function prototypes 
void addUser(); 
void part1(); 
int main(); 

//global variables 
    string username; 
    string password; 
    int balance; 
void addUser(){ 
    //open a file in write mode 
     ofstream myfile; 
     myfile.open("userinfo.txt", ios::app);//append the text file 
     if(myfile.is_open()){ 
     cout<<"Please Create a Username: "; 
     string inputCheck;//a string to compare name 
     cin>>inputCheck; 
     cout<<"Please Create a Password: "; 
     cin>>password; 
     cout<<"Current Balance: "; 
     cin>>balance; 
     myfile<<inputCheck<<' '<<password<<' '<<balance<<"\n"; 
     myfile.close(); 
     cout<<"User account '"<<inputCheck<<"' has been created"<<endl; 
     }//ends create a password else 
    part1(); 
} 

void part1() 
{ 
    cout<<"1.Add User\n2.Edit Information"<<endl; 
    int input; 
    cin>>input; 
    if(input == 1){ 
     addUser(); 
    }else if(input == 2){ 
    //find the user 
    cout<<"Enter the username: "; 
    string checkUser; 
    cin>>checkUser; 
    ifstream infile("userinfo.txt"); //CREATING IFSTREAM 
    ofstream outfile("pleasework.txt"); 
    bool foundUser = false; 
    while(infile>>username>>password>>balance){ 
     if(checkUser==username){ 
     foundUser = true; 
     break; 
     } 
    } 
    if(foundUser){ 
    cout<<"Current Balance: "<<balance<<endl; 
    cout<<"Enter new balance: "; 
    int newBalance; 
    cin>>newBalance;  
    if(infile.is_open()){ 
     outfile<<username<<' '<<password<<' '<<newBalance<<endl; 
     //How do I get all of the other unedited accounts in here?!?!?!?! 
     } 
    }//end input 2 
     infile.close(); 
outfile.close(); 
    } 

}//end part 1 

int main(){ 
    part1(); 
} 

Answer 1

下面是一些伪代码，这可能有助于：

方法1：

open existing file in 'read' mode 
open new file in 'write' mode 
for each line in existing: 
    if line doesn't need update: 
     write line to new file 
    else: 
     make changes to values from line 
     write updated line to new file 
close existing file 
close new file 
move new file over existing file 

方法2：

open existing file in 'read/write' mode 
data = array of lines 
for each line in existing: 
    read values into data 
clear existing file 
add/delete rows in data if necessary 
for each row in data: 
    update values in row 
    write updated line to existing file 
close existing file 

Answer 2

呼叫

main(); 

以递归方式给你留下未定义的行为。所以你不能指望任何可靠的东西。