CODEWITHSUNDEEP
c-preprocessor
Phylliida
Phylliida

Reputation: 4383

Why do c preprocessor directives ignore the \ newline rule when it is followed directly after a #?

Normally, via the standards, any \ followed directly by a newline is converted into the code without the newline and backslash. For example:

int yams\
yams;

turns into

int yamsyams;

and

int cheese // blerg \
more blerg

turns into

int cheese // blerg more blerg

This behavior can be nice with very long single line code.

However, it seems that

#\
This code not part of the macro

While

#a\
This code is part of the macro.

And even

#        \
This code is not part of the macro

While

#    a\
This code is part of the macro

Why is this the one exception to the "\ newline" being removed rule?

Upvotes: 4

Views: 570

Answers (1)

Jonathan Wakely
Jonathan Wakely

Reputation: 171303

As described in [lex.phases], replacing the backslash-newline is done by the preprocessor, and should happen very early, in phase 2, which is before splitting the source into preprocessor tokens (phase 3) and before handling preprocessor directives such as #define or #include (phase 4).

So in all your examples you should see the backslash-newline removed.

Upvotes: 3

Related Questions