使用I / O流从一个文件读取并写入另一个文件

Question

I'm going through a text-book where an exercise entails copying text from one file and write it's lower-case equivalent to another file. I can't seem to find a way to do that using just I/O streams (most of the solutions I found online use stream buffers).

My code is this

int main()
{
string f_name1, f_name2;
cout << "enter the file names" << '\n';

cin >> f_name1>>f_name2;
ofstream fs{ f_name1 };
ifstream fsi{f_name1};
ofstream fs2{f_name2};

fs << "LoRem ipSUM teXt TaXi";

char ch;

while (fsi.get(ch)) {


    fs2 << ch;
}

After running nothing is written to the second file (f_name2). It's just a blank file.

Edit:

This doesn't work either

int main()
{
string f_name1, f_name2;
cout << "enter the file names" << '\n';

cin >> f_name1>>f_name2;
ofstream fs{ f_name1 };
ifstream fsi{f_name1};
ofstream fs2{f_name2};

fs << "LoRem ipSUM teXt TaXi";

char ch;

while (fsi>>ch) {


    fs2 << ch;
}

}

Answer 1

1. You are complicating your task for no apparent gain. There is no need for

    ofstream fs{ f_name1 }; fs << "LoRem ipSUM teXt TaXi"; 

2. Use a text editor and create the contents of the input file outside the program.

Here's an updated version of your main fuction:

int main()
{
   string f_name1, f_name2;
   cout << "enter the file names" << '\n';

   cin >> f_name1 >> f_name2;

   ifstream fs1{f_name1};
   if ( !fs1 )
   {
      std::cerr << "Unable to open " << f_name1 << " to read from.\n";
      return EXIT_FAILURE;
   }

   ofstream fs2{f_name2};
   if ( !fs2 )
   {
      std::cerr << "Unable to open " << f_name2 << " to write to.\n";
      return EXIT_FAILURE;
   }

   // Using ostream::put() seems the right function to use
   // for writing when you are using istream::getc() for reading.
   char ch;
   while (fs1.get(ch))
   {
      fs2.put(std::tolower(ch));
   }
}

Answer 2

Hmm. So you're writing to the file and then reading the contents and writing out again. Okay...

You might need to fs.flush() after the fs << code. The data can be buffered, waiting for a newline character to trigger a flush, or doing one yourself.

I'd also put in some print statements in your while loop to make sure you're getting what you think you're getting.