This is a royal pain to have to convert or even more annoying to have to rig your programs to read data the wrong way on the other platform.
The advantage of using a text file based format (like XML) is that text files are pretty much read and written to the exact same way no matter the bit order on your OS. Using something like an XML library has the added advantage of a node system so its even easier to read your attributes and values instead of having to parse everything. Plus the added flexibility of being able to script your data quazi-HTML style.
You could use something like JSON or even Lua, which people have also recommended for adding a higher level of functionality. I like how simple XML is however.
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