Linux，c ++，负退出代码，澄清？

Question

In Linux, c++ can we return exit codes? ie is this code valid:

int main()
{
  return -1;
}

The reason I am asking if this code is compiled and executed from bash/zsh, the return value would be 255, I thin this due to the fact that its using an 8 bit return code, and that implies that return codes are only allowed to be between positive.

Is this correct?

Answer 1

The relevant system call is _exit() , and POSIX itself specifies that only the bottom 8 bits of the status given to _exit() are normally usable:

_exit(status)
The value of status may be 0 , EXIT_SUCCESS , EXIT_FAILURE , or any other value, though only the least significant 8 bits (that is, status & 0377 ) shall be available from wait() and waitpid() ;

Though it goes on to say that "the full value shall be available from waitid() ", but on Linux, I seem to still get just the low eight bits.

Answer 2

NO, exit code passed to exit(2) is merged with data for cases in which your program is interrupted by means of a signal sent to it. exit(2) return code is only the least signifiant byte of the code returned by wait(2) . See pages for wait(2) and exit(2) for an explanation of how the return code is formed.