C++ Exceptions – Is throwing c-string as an exception bad?

It is much better to throw a standard exception object. In general, the best practice is to throw something derived from std::exception so that if in some situation it does cause your program to terminate, the implementation has a better chance of printing a useful diagnostic.

Because it isn’t hard to do this, I would never recommend throwing a raw string literal.

#include <stdexcept>

void someFunction()
{
    try {
        // code
        if (some error) {
            throw std::runtime_error( "Description of error." );
        }
    }
    catch (const std::exception& ex) {
        std::cerr << ex.what() << "\nFatal error" << std::endl;
    }
}