Valid characters for file name in the #include directive
<p>What are the valid characters for the file name in the <code>#include</code> directive?</p>

<p>Under Linux, for example, I can use pretty much any character except <code>/</code> and <code>\0</code> to have a valid file name, but I would expect C preprocessor to be more restrictive about the names of files I can include.</p>