Why do multi-line macros have backslashes at the end of each line?

Question

In a macro declaration like:

#define WAIT_SPI2_TRANSMISSON_END() {while ((SPI2_SR & SPI_SR_TXCTR_MASK) != 0) {\\
                                     if(         


        

Answer 1

It is so called continued line. It means that your line is continued in line that follows. It is simply sometimes easier to read stuff if written this way.

BTW - continued lines are 'glued' at preprocessor pass.

Read here about step #3: gcc docs

Excerpt:

 /\
 *
 */ # /*
 */ defi\
 ne FO\
 O 10\
 20

is equivalent to:

#define FOO 1020

It is noteworthy to say that continued lines do not have to be used within preprocessor macros. It is perfectly legal top write this:

f\
lo\
at f = 5.0; 

which is the same as:

float f = 5.0;