Red Hat Bugzilla – Bug 43110
Preprocessor misinterprets multiple concatinations
Last modified: 2007-04-18 12:33:30 EDT
From Bugzilla Helper: User-Agent: Mozilla/4.77 [en] (X11; U; Linux 2.4.2-2smp i686) Description of problem: When the preprocessor encounters The preprocessor throws an error at me when it encounters double concatinations How reproducible: Always Steps to Reproduce: The following code, run through the preprocessor (gcc -E) gives an error. With egcs (egcs -E) it works #define MC_FUNC(op,xy) \ static void motion_comp_##op####xy##_16x16_c MC_FUNC(put,); Actual Results: the preprocessor bundeled with gcc 2.96 gives me warning: pasting "motion_comp_put" and "##" does not give a valid preprocessing token Expected Results: I was hoping to get static void motion_comp_put_16x16_c ; as output from the preprocessor Additional info:
The C standard sais if pasting two tokens with ## does not create a valid preprocessor token, then the behaviour is undefined. gcc has a warning about this, so that you can fix the code, if you use just a single ## it will work just fine. The fact that it used to work with older gcc cannot be an excuse or broken code.