Three streams just exist: cout (terminal output), cin (terminal input), and cerr (error output, which also goes to the terminal).When writing error messages, use cerr rather than cout. In simple examples, the two appear to be the same. However, they behave differently when you use Unix redirection operators when you run your program. In particular, if you redirect output to a file, error messages printed to cerr will still appear on the user's terminal whereas error messages printed to cout will be mixed into the output file.File streams are of type ifstream (input) or ofstream (output).ifstream fp_in; // declarations of streams fp_in and fp_outofstream fp_out;fp_in.open("myfile.txt", ios::in); // open the streamsfp_out.open("myfile.txt", ios::out);fp_in.close(); // close the streamsfp_out.close(); A file should be closed if you are done with it, but the program will continue running for a while longer. This is particularly important when you intend to open a lot of files, as there may be a limit on how many you can have open at once. It is also a good idea if you intend to open a file for input, and then re-open the file for output.Declaring the pointer and opening the file can be combined:ifstream fp_in("myfile.txt", ios::in); // declare and openThe parameters ios::in and ios::out specify the mode in which the file is to be opened. Depending on the implementation of C++, it may be possible to specify a variety of other mode options, such as appending to the end of an existing file, triggering an error rather than overwriting an existing file, or specifying that a file is binary for operating systems (e.g. MS-DOS) which distinguish binary and ASCII files. C++
Topic: I/o operations
How to getting a stream in i/o ?
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