How do I enable C++ styled comments in gcc while leaving ANSI enabled?
On recent releases of gcc, -ansi is documented as being the same as -std=c89. The new comment syntax is only available with the C99 standard, so -std=c99 would allow it.
There is also -std=gnu89, which is the same as -std=c89 but allowing all gcc extensions (including the C++-style comment syntax, which was a GNU extension long before it was added to the standard).
Also look at the -pedantic flag, which could give you some useful warnings.
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