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The only solution for mitigating ambiguity of a file, such as my_libraryOLD.h, is to rename old files with either a prefix (that would fall within the first eight characters) or add an extension (such as my_library.h.old).
Exceptions
PRE08-C-EX1: Although the C Standard requires only the first eight characters in the file name to be significant, most modern systems have long file names, and compilers on such systems can typically differentiate them. Consequently, long file names in headers may be used, provided that all the implementations to which the code is ported can distinguish between these file names.
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