5.7 Line Continuation

The sequence of a backslash and a newline is ignored absolutely anywhere in a C program. This makes it possible to split a single source line into multiple lines in the source file. GNU C tolerates and ignores other whitespace between the backslash and the newline. In particular, it always ignores a CR (carriage return) character there, in case some text editor decided to end the line with the CRLF sequence.

The main use of line continuation in C is for macro definitions that would be inconveniently long for a single line (see Macros).

It is possible to continue a line comment onto another line with backslash-newline. You can put backslash-newline in the middle of an identifier, even a keyword, or an operator. You can even split ‘/*’, ‘*/’, and ‘//’ onto multiple lines with backslash-newline. Here’s an ugly example:

/\
*
*/ fo\
o +\
= 1\
0;

That’s equivalent to ‘/* */ foo += 10;’.

Don’t do those things in real programs, since they make code hard to read.

Note: For the sake of using certain tools on the source code, it is wise to end every source file with a newline character which is not preceded by a backslash, so that it really ends the last line.