Converts C/C++ preprocessor include guards from the #ifndef XY_H, #define XY_H to the #pragma once paradigm.

Header files have the problem that they should be included once per compile unit; thus, they usually deploy a scheme that looks like this

/*
 * some funky comment, doxygen, copyright info
 */
#ifndef MY_HEADERFILE_H
#define MY_HEADERFILE_H

class declare_and_define_whatever_you_want
{
...
};
#endif /* maybe a comment that this belongs to MY_HEADERFILE_H */

Since this lead to a few bugs (namely, sometimes there are #define naming conflicts, or copy&paste errors), I've wrote a script to make the same file look like this:

/*
 * some funky comment, doxygen, copyright info
 */
#pragma once

class declare_and_define_whatever_you_want
{
...
};

• C preprocessor (only tested with the GCC cpp)
• python 2.3+ (I think. Tested with 2.7.5)

• The include guards should be the surround the whole semantic content of the file. That means that #ifndef must be on the first non-comment, non-whitespace, non-empty line of your source code and that it must end with the matching #ifndef line, which may only be followed by empty or whitespace-only lines.
• The #define constants must be UPPERCASE_UNDERSCORE_0_TO_9_ONLY style.