Question

So I’ve created a simple test application. It’s purpose is to either read or write to a text file. It’s looking for the string “Firmware: “. The idea is that a device will have a package transferred to it and stored, then activated. I want to store the name of that package (Ex: Update1) and when I need to, query that and get the package name back (Read from the file).

Problem 1: It doesn’t seem to be writing to the file.
Problem 2: When I get it to write to the file, in the case in which the line “Firmware: pkgName” exists, how do I replace pkgName with the new package name?

This program runs and compiles, so feel free to throw it in an IDE or text editor, it just doesn’t fully do what I want. I am using log.txt as my sample file to read from. I’m sure there’s a more simple way to do this. I’ve been at this for some time and I’ve become stumped.

Thanks for the help!

#include <cstdlib>
#include <iostream>
#include <string>
#include <fstream>

using namespace std;

int writeFile(string filename, string pkgName);
int readFile(string filename);

int main(void) {
    string filename = "log.txt", userInput, pkgName;
    system("touch log.txt");

    while (true) {
        cout << "Write or Read?\n>>>";
        cin >> userInput;

        if (userInput == "Write") {
            cout << "What's your package name?\n>>>";
            cin >> pkgName;
            writeFile(filename, pkgName);
        } else if (userInput == "Read") {
            readFile(filename);
        } else {
            cout << "Invalid Input";
        }
    }
}

int writeFile(string filename, string pkgName) {
    bool found, exists = true;
    string line, word;
    fstream firmwareFile;
    int pos, size, num = 1;
    firmwareFile.open(filename.c_str(), ios::in | ios::out | ios::app);
    //firmwareFile << "This is a test.";
    if (firmwareFile.is_open()) {
        while (!found) {
            getline(firmwareFile, line);
            pos = line.find("Firmware: ");
            if (pos != string::npos) {
                //Found It
                found = true;
                exists = true;
                size = line.size();
                word = line.substr(10, ((size - pos) + 10));
                cout << word << " is the old package name" << endl;
                //TODO - Replace that with the new package name
                firmwareFile.close();
            } else if (firmwareFile.eof()) {
                //Doesn't Exist
                found = true;
                exists = false;
                cout << "No last firmware package available.\n";
            } else {
                //Still Looking
                found = false;
                cout << "Searching line #" << num <<  endl;
            }
            num++;
            if (!exists) {
                firmwareFile << endl << "Firmware: " << pkgName << endl;
                cout << "Wrote package name to file\n" << endl;
            }
            firmwareFile.close();
        }   
    } else {
        cout << "Unable to open file";
    }
}

int readFile(string filename) {
    bool found;
    string line, word;
    fstream firmwareFile;
    int pos, size, num = 1;
    firmwareFile.open(filename.c_str(), ios::in | ios::out | ios::app);
    if (firmwareFile.is_open()) {
        while (!found) {
            getline(firmwareFile, line);
            pos = line.find("Firmware: ");
            if (pos != string::npos) {
                found = true;
                size = line.size();
                word = line.substr(10, ((size - pos) + 10));
                cout << word << endl;
            } else if (firmwareFile.eof()) {
                found = true;
                cout << "No last firmware package available.\n";
                firmwareFile << endl << "Firmware: ";
            } else {
                cout << "Searching line #" << num << endl;
            }
            num++;
        }
        firmwareFile.close();
    } else {
        cout << "Unable to open file";
        firmwareFile.close();
    }
    firmwareFile.close();
}

Here is the contents of my log.txt file (Everything but the line containing “Firmware: ” is trivial)

You
Think
It's
Here
But
It's
Not
So
That
Sucks
Doesn't
It
?
Firmware: Update1
I
Hope
You
Caught
It
!

Answer 1

You can simplify things if you write another file with only the relevant line changed:

std::ifstream cfg("log.txt");
std::ofstream tmp("log.tmp");
std::string line;
std::string pkgName;

while(std::getline(cfg, line)) {
    if (line.find("Firmware:") != std::string::npos) {
        line = "Firmware: " + pkgName; 
    }
    tmp << line << '\n';
}

Now, renaming and deleting files is platform specific. If you want a portable solution, I suggest you look into Boost Filesystem library.