C++:搜索并写入文件以替换字符串

所以我创建了一个简单的测试应用程序。它的目的是读取或写入文本文件。它正在寻找字符串"固件："。这个想法是，一个设备将有一个包转移到它上面并存储，然后激活。我想存储该包的名称（例如：Update1），当我需要时，查询它并获取包名称（从文件中读取）。

问题1:它似乎没有写入文件。问题2:当我将其写入文件时，如果存在"Firmware：pkgName"行，我如何用新的程序包名称替换pkgName？

这个程序运行和编译，所以可以把它放在IDE或文本编辑器中，它只是不能完全实现我想要的。我正在使用log.txt作为我的示例文件进行读取。我相信有一种更简单的方法可以做到这一点。我已经做了一段时间了，我已经被难住了。

谢谢你的帮助！

#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 filen" << 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();
}

以下是我的log.txt文件的内容（除了包含"Firmware："的行之外，其他内容都很琐碎）

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