Why did the 16-bit _lopen and _lcreat function return -1 on failure instead of 0?

Raymond Chen

Some time ago, I discussed why HANDLE return values are so inconsistent, and I traced it all the way back to the 16-bit _lopen and _lcreat functions, which returned -1 on failure.

But why do those functions return -1 on failure instead of zero?

The _lopen and _lcreat functions were Windows versions of the C runtime _open and _creat functions. The C runtime functions came in four different versions depending on which MS-DOS memory model you were using, and the convention was that when Windows adopted a C runtime function, it used the “large” version with the L prefix, since that is the most general version.

Okay, so why did _open and _creat return -1 on failure?

Because they were MS-DOS-compatible versions of the Unix functions open and creat. They even preserve the dropped silent “e” at the end of creat.

Okay, so why do those functions return -1 on failure?

On Unix, the return value is an integer that represents a file descriptor, valid file descriptors are integers starting with zero. Every process comes with three predefined file descriptors:

Descriptor Meaning
0 stdin (standard input)
1 stdout (standard output)
2 stderr (standard error)

Files opened by the program begin with file descriptor 3.

The value -1 is used to represent failure because 0 was already taken.

And that value of -1 carried forward, through a chain of backward compatibility, to Win32 as the numeric value of INVALID_HANDLE_VALUE. We saw a little while ago one of the consequences.

3 comments

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  • Neil Rashbrook 1

    Or at least, every Unix process assumes that it comes with three predefined file descriptors. There’s nothing to stop you writing something like foo <&- to launch a process without a STDIN handle, but the process might not appreciate it.

    • skSdnW 0

      xcopy.exe is not happy if you don’t give it a stdin.

    • Kevin Norris 1

      It’s easy to break the assumptions of Unix programmers. There are programs that change their behavior depending on the value of argv[0], usually because you’re supposed to make one or more symlinks with different names. I have to wonder what those programs do if you pass an empty argument list (POSIX says the application “should” ensure that the binary name is given as argv[0], but in their base definitions, “should” indicates a portability recommendation rather than a strict requirement, so this is at least somewhat POSIX-legal). In that case, ISO C (and by extension POSIX) require that argv[0] == NULL, but POSIX also warns that some applications may dereference it without checking for NULL.

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