PeekNamedPipe失败，但GetLastError返回0

Question

I'm confused by the Windows API. I try to see if there are bytes left in an anonymous pipe using PeekNamedPipe . This function fails, but GetLastError() does not return an error.

The relevant part of my code is

if( !PeekNamedPipe( handle, NULL, 0, NULL, &numBytesAvailable, NULL ) )
  throw PeekNamedPipeException( "GetLastError() returned " + std::to_string( GetLastError() ) );

This throws an error, generating the following message:

terminate called after throwing an instance of 'PeekNamedPipeException'
  what():  GetLastError() returned 0

But if PeekNamedPipe fails, GetLastError should not return 0 ( == ERROR_SUCCESS ), right?

Thank you for your help!

Answer 1

It's probably because more system functions are called (behind the scenes) between the PeekNamedPipe and your call to GetLastError .

Store the value from GetLastError in a temporary variable, and use that when constructing the string.