Bool NullFunc(const struct timespec *when, const char *who)
{
   return TRUE;
}

#define UNUSED(x) (void)(x)

void f(int x) {
    UNUSED(x);
    ...
}

auto lambda = [](workerid_t workerId) -> void { };

auto lambda = [](__attribute__((unused)) _workerid_t workerId) -> void { } ;

#ifdef __GNUC__
#  define UNUSED(x) UNUSED_ ## x __attribute__((__unused__))
#else
#  define UNUSED(x) UNUSED_ ## x
#endif

#ifdef __GNUC__
#  define UNUSED_FUNCTION(x) __attribute__((__unused__)) UNUSED_ ## x
#else
#  define UNUSED_FUNCTION(x) UNUSED_ ## x
#endif

void foo(int UNUSED(bar)) { ... }

static void UNUSED_FUNCTION(foo)(int bar) { ... }

int foo (__attribute__((unused)) int bar) {
    return 0;
}

void foo(int __attribute__((unused))key)
{
}

void foo(int key)
{
   int hash = 0;
   int bkt __attribute__((unused)) = 0;

   api_call(x, hash, bkt);
}

#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wunused-parameter"
<code with unused parameters here>
#pragma GCC diagnostic pop

If (MSVC)
    Set (CMAKE_EXE_LINKER_FLAGS "$ {CMAKE_EXE_LINKER_FLAGS} / NODEFAULTLIB: LIBCMT")
    Add_definitions (/W4 /wd4512 /wd4702 /wd4100 /wd4510 /wd4355 /wd4127)
    Add_definitions (/D_CRT_SECURE_NO_WARNINGS)
Elseif (CMAKE_COMPILER_IS_GNUCXX OR CMAKE_COMPILER_IS_GNUC)
    Add_definitions (-Wall -W -pedantic)
Else ()
    Message ("Unknown compiler")
Endif ()

if (when || who || format || data || len);

void foo(int x) {
    x; /* unused */
    ...
}