如何在文本文件中添加空格？

Question

I have a text file like this:

100,Nguyen Van A,2004
101,Tran Thi B,2004
102,Vo Van C,2005
103,Truong Thi D,2005

How can I add one blank space right after each "," into that file using C++?

I've tried using find() function but nothing worked.

svFile.open("list_student.txt");
    while (getline(svFile, line, ','))
    {
        if (line.find(",", 0) != string::npos)
            svFile << " ";
    }

Answer 1

Two options, read and write the file character by character, or option 2, read the entire text file into a string and then perform your required changes and write the file back:

Option 1 (Character by Character):

 char ch;
 fstream fin("list_student.txt", fstream::in);
 fstream fout("list_student_result.txt", fstream::out);
 while (fin >> noskipws >> ch) {
    fout << ch;
    if (ch==',')
    {
        fout << ' ';
    }
 }
 fout.close();

Option 2 (Read/Write entire file):

#include <iostream>
#include <fstream>
int main()
{

    // Read the entire file
    std::ifstream t("list_student.txt");
    std::stringstream buffer;
    buffer << t.rdbuf();

    std::string myString = buffer.str();
    size_t start = 0;
    int pos = 0;

    // Set your start character and replace with string here
    std::string comma(",");
    std::string replaceWith(", ");

    // Replace the comma "," with ", " (and a space)
    while ((pos = myString.find(comma, pos)) != std::string::npos) {
        myString.replace(pos, comma.length(), replaceWith);
        pos += replaceWith.length();
    }

    // Write the formatted text back to a file
    std::ofstream out("list_student_result.txt");
    out << myString;
    out.close();

    return 0;
}