GetExitCodeProcess

GetExitCodeProcess is used to check the exit code of a process. By convention in Windows, Unix and in C++, exit code 0 (e.g. as returned from main) denotes success. In C++ this value is available as the macro symbol EXIT_SUCCESS from <stdlib.h>. On other systems EXIT_SUCCESS needs not be 0, but in C++ exit code 0 always denotes success, possibly in addition to the value of EXIT_SUCCESS.

The Windows and Unix-land convention is that any other exit code denotes failure, but the only portable failure value in C++ is the one denoted by EXIT_FAILURE. In Windows this is conventionally the value 1. Unfortunately that conflicts with the value of a Windows error code, about “incorrect function” (as reported by errlook.exe). For this reason one may choose to use Windows' own general failure value E_FAIL to indicate a general failure, instead of using the portable but imperfect EXIT_FAILURE.

Two relevant differences between Windows and Unix-land:

• In Windows a non-zero exit code is often an error code that tells you something about the cause of failure. It can be passed to a tool such as Microsoft's errlook to get a textual description, the same as via the API function FormatMessage. In Unix-land process exit codes used as failure cause indications are much less common.
• In Unix-land tools can generally be relied on to indicate failure or success via the exit code. This is not so in Windows. Even many of the built-in and standard commands fail to do so.

Especially the latter point is important for use of GetExitCodeProcess. You need to know that the process you're checking, is one that produces a meaningful exit-code.

Also note well that the code STILL_ACTIVE is defined as a low number, as I recall around 270 or thereabouts, and can be produced by a process, so that it is not a reliable indicator of whether a process is still active or not. I.e., don't use GetExitCodeProcess to poll for a process to finish. Depending on the process & circumstances, such code might hang.