C++ Detect input redirection [duplicate]

Answer 1

In standard C++, you can't. However on Posix systems you can using isatty:

#include 
#include 

int const fd_stdin = 0;
int const fd_stdout = 1;
int const fd_stderr = 2;

int main()
{
  if (isatty(fd_stdin)) 
    std::cout << "Standard input was not redirected\n";
  else
    std::cout << "Standard input was redirected\n";
  return 0;
}