[Mingw-msys] Re: Using spawnvp

[Angus L. <le...@ly...>]

Keith MARSHALL wrote:
>>Thanks, Keith, but I plan to move to CreateProcess instead. Code 
>>written. Further stress testing needed.
> 
> So, you still have the same problem;  Microsoft's implementations
> of `spawn' and `exec' are themselves wrappers for `CreateProcess',
> and it's the argument passing through `CreateProcess' which is
> broken -- it simply passes all the arguments as a single string,
> leaving the child process to reparse this, as its command line!

Understood.

> It may still be worth your while to have a look at the quoting
> routine in the wrappers Jeff and I wrote -- it's been pretty
> thoroughly tested already.

Thanks, I'll look. But I assume that it's the same as the stuff below, no?

> Also remember, that if you abandon `spawn' and `exec' in favour of
> `CreateProcess', your code becomes potentially more difficult to
> port to non-MS-Windows platforms in the future.

Nahhh. I'm going the other way, porting LyX (www.lyx.org) to windoze.

Angus

// Inside a "-protected block, any " character must be escaped.
// Note also that all adjacent \ characters in a block must be escaped
// only if the next character following them is a " (which must
// also be escaped).
// Thus, using <...> to delimit the string,
// <foo \ bar> becomes <"foo \ bar">,
// <foo " bar> becomes <"foo \" bar"> and
// <foo \\" bar> becomes <"foo \\\\\" bar">.
// See http://article.gmane.org/gmane.comp.lib.boost.user/3005
// or http://msdn.microsoft.com/library/en-us/vccelng/htm/progs_12.asp

std::ostringstream new_arg;

std::string::const_iterator it = old_arg.begin();
std::string::const_iterator const end = old_arg.end();

new_arg << '"';

for (; it != end; ++it) {
     char const c = *it;

     if (c == '"') {
         new_arg << "\\\"";

     } else if (c == '\\') {
         std::string::const_iterator it2 = it + 1;
         while (it2 != end && *it2 == '\\')
             ++it2;

         std::string::size_type nbackslashes = std::distance(it, it2);
         if (it2 != end && *it2 == '"')
             nbackslashes *= 2;

         new_arg << std::string(nbackslashes, '\\');
         it = it2 - 1;

     } else {
         new_arg << c;
     }
}

new_arg << '"';