Quoting Command-line Arguments

Raymond Chen recently blogged about the way CommandLineToArgvW treats quotes and backslashes. Parsing the command-line into argv[] is something I have had to fight with as well, so besides pointing to Raymond’s excellent post, I wanted to add a few comments of my own here.

We are examining how command-line arguments with spaces and quotes are handled. Part of the problem comes from the fact that DOS/Windows uses backslash as separator in paths. On systems like Unix, where forward slash is used instead, using backslash to escape special characters is less of a problem. But if you ever put a Windows path in a C string literal, you may have run into LTS — the situation where a string becomes unreadable due to escape characters.

Microsoft fixed this in C# with verbatim string literals. C# also implements a simpler method of escaping a quote inside a quoted string — doubling it — which is used in languages like Pascal and BASIC, and is what Raymond’s second hypothetical set of rules suggest.

The compromise we get for parsing command-line arguments in the C runtime library (and CommandLineToArgvW) is documented on MSDN. What the MSDN documentation does not tell you is that there is a second mechanism for inserting a literal quote in a quoted string — or at least there might be, depending on which version of the C runtime library.
Continue reading Quoting Command-line Arguments