Newlines in Arguments (The C Preprocessor)

#### 3.10.7 Newlines in Arguments ¶

The invocation of a function-like macro can extend over many logical lines. However, in the present implementation, the entire expansion comes out on one line. Thus line numbers emitted by the compiler or debugger refer to the line the invocation started on, which might be different to the line containing the argument causing the problem.

Here is an example illustrating this:

    #define ignore_second_arg(a,b,c) a; c

    ignore_second_arg (foo (),
                       ignored (),
                       syntax error);

The syntax error triggered by the tokens `syntax error` results in an error message citing line three—the line of ignore_second_arg— even though the problematic code comes from line five.

We consider this a bug, and intend to fix it in the near future.