Write a C++ program that implements flipping the contents of each line of a string in a text file and outputs the flipped result to another text file. Both the input file name and output file name are specified by the user.

Sure, here's a C++ program that implements flipping the contents of each line of a string in a text file and outputs the flipped result to another text file.

#include <iostream>
#include <fstream>
#include <string>
#include <algorithm>

using namespace std;

int main()
{
    string inputFileName, outputFileName;
    cout << "Enter input file name: ";
    cin >> inputFileName;
    cout << "Enter output file name: ";
    cin >> outputFileName;

    ifstream inputFile(inputFileName);
    if (!inputFile.is_open())
    {
        cout << "Failed to open input file!" << endl;
        return 1;
    }

    ofstream outputFile(outputFileName);
    if (!outputFile.is_open())
    {
        cout << "Failed to open output file!" << endl;
        return 1;
    }

    string line;
    while (getline(inputFile, line))
    {
        reverse(line.begin(), line.end());
        outputFile << line << endl;
    }

    inputFile.close();
    outputFile.close();

    cout << "File has been flipped and saved successfully!" << endl;

    return 0;
}

The program first prompts the user to enter the input file name and output file name. It then opens the input file and output file using `ifstream` and `ofstream`, respectively. If either file cannot be opened, the program reports an error and exits.

The program then reads each line from the input file using `getline`, reverses the line using `reverse`, and writes the reversed line to the output file using `outputFile << line << endl`. Finally, the program closes both files and reports success.

Note that this program assumes that the input file contains one line of text per line, and that each line ends with a newline character. If the input file does not conform to this format, the program may not work correctly.