HP C B.11.11.16 Release Notes

HP C/ANSI C Release Notes

Problem Description and Fixes

Chapter 128

However, you can also insert whitespace to the left of the left operand of ## to more

accurately specify the intended left operand.

For example, if you use

#define foo(f, s...) printf(f, s)

Then the macro call

foo(“Hello world.\n”);

results in the expansion

printf(“Hello world.\n”,);

(Note the comma ",") causing a syntax error.

GNU provides the following workaround for this kind of a situation. If you use:

#define foo(f, s...) printf(f, ## s)

If the variable parameter s is non-null, and if you use:

foo("%s %d\n", "Cycles", "1024");

The result is:

printf("%s %d\n", "Cycles", "1024");

as the expansion as you would expect.

However, if s is null, this erases the comma to the left of the ## in the macro deﬁnition

and resulting expansion is:

printf("Hello world.\n");

Note that the comma is removed.

In order to get the same behavior in HP C, you must insert a space to the left of the

comma to make it clear to the preprocessor that the comma is the left operand of the ##

operator. Thus your deﬁnition for the macro foo is:

#define foo(f, s...) printf(f , ## s)

(Note the space to the left of the ## operator in the macro deﬁnition.)

If the space is not inserted, the left operand of the ## operator is understood to be:

printf(f ,.

Because there is no parameter by that name for foo, it is erased.

When specifying declarations within code in the HP C/ANSI C compiler, do