NAME
__USE —
compile time macro that marks a
variable as being used
SYNOPSIS
#include
<sys/cdefs.h>
void
__USE(x);
DESCRIPTION
The__USE macro can be used to omit warnings produced by
certain compilers when variables are being set, but not used in a function.
There are cases where it is simpler to mark a variable as used, as opposed to ifdef out its use:
#ifdef DEBUG_FOO
#define DPRINTF(a) printf a
#else
#define DPRINTF(a)
void
foo(void) {
int var;
var = getval();
DPRINTF(("val is %d0, var));
}
In this case, ifdefing the code would make it:
void
foo(void) {
#ifdef DEBUG_FOO
int var;
var = getval();
DPRINTF(("val is %d0, var));
#else
(void)getval();
#endif
}
This is not desirable because it duplicates code. With the
__USE macro this can be written as:
void
foo(void) {
int var;
var = getval();
#ifdef DEBUG_FOO
DPRINTF(("val is %d0, var));
#else
__USE(var);
#endif
}
without producing compiler warnings.
Although it is simple to write:
(void)var;
abstracting this into the macro allows for alternate implementations, as well as changing it to an empty implementation so that the liveness of the variable can be re-evaluated.
IMPLEMENTATION NOTES
__USE is implemented as:
#define __USE(a) ((void)(a))
SEE ALSO
CAVEATS
__USE should be used sparingly as it can
cause valid warnings to be hidden.
Use of this macro is non-portable; this is part of the implementation namespace and should only be used in NetBSD code.