fstream does not save changes C++

Question

I made a program that is supposed to be a simple text editor that can create (if not existed) a .cpp file, read the content of the file and display it on the console, and modify the content and save the changes when Ctrl+S is pressed.

The program does all the above, except saving the changes. Can anybody explain what the problem is?

Here is below the full code:

#include <iostream>
#include <fstream>
#include <filesystem>

namespace fs = std::filesystem;
void work(std::fstream& file, const std::string& path)
{
    std::string previous;
    while (not file.eof()) {
        std::getline(file, previous);
        if (not previous.empty())
            std::cout << previous << '\n';
    }
    char c;
    std::string buff;
    while (true) {
        c = std::cin.get();
        buff += c;
        switch (c) {
            case 19:
                if (not file.is_open()) {
                    file.open(path, std::ios::in | std::ios::out);
                    if (not file.is_open()) {
                        std::cerr << "Unable to open!" << std::endl;
                        exit(EXIT_FAILURE);
                    }
                }
                file.seekp(0, std::ios::end);
                buff.pop_back();
                for (char x : buff)
                    file.put(x);
                std::cout << "Saved!" << std::endl;
                buff.clear();
                file.close();
                break;
            default:
                continue;
        }
    }
}

int main()
{
    const std::string path = "D:\\some_file.cpp";
    if (not fs::exists(path)) {
        std::ofstream new_file(path);
        if (not new_file.is_open()) {
            std::cerr << "Unable to create the file!" << std::endl;
            return EXIT_FAILURE;
        }
        else
            new_file.close();
    }
    std::fstream file(path, std::ios::in | std::ios::out);
    work(file, path);
}

Probably unrelated: [Watch out for `while(not file.eof())`](https://stackoverflow.com/q/5605125/4581301) — user4581301, Jul 10 '23 at 19:20
Side note: Never post the full code. Post a [mre]. Odds are really good that you'll find the mistake while making the minimal example and not have to ask the question. — user4581301, Jul 10 '23 at 19:21
Recommendation: In `case 19:` without context 19 is meaningless. You want to use terms that describe what's really happening in the code and what the 19 stands for. — user4581301, Jul 10 '23 at 19:25
Good to know. Incorporate that into the identifier name so you don't have to tell people. — user4581301, Jul 10 '23 at 19:30
@n.m.willseey'allonReddit it actually prints ^s with the message "Saved!" but it never saves the changes — Zerocool_m12, Jul 10 '23 at 19:49

score 3 · Accepted Answer · answered Jul 10 '23 at 19:44

At the end of the first while loop in work, file must be in the eof state (or worse). If a stream has any flags set then all subsequent operations on the stream will immediately fail and do nothing. To return the stream to a working state you need to call file.clear().

Also note that while (not file.eof())) is usually incorrect as it will read an extra line. You should do this instead:

while (std::getline(file, previous)) {
    std::cout << previous << '\n';
}

fstream does not save changes C++

1 Answers1