variants c

//(I)

#define INSTANCE_LAYER_COUNT 2
const char *g_pInstanceLayers[] = {"VK_LAYER_NV_optimus","VK_LAYER_LUNARG_standard_validation"};

//#define INSTANCE_LAYER_COUNT 0
//const char *g_pInstanceLayers[] = {0};

#if INSTANCE_LAYER_COUNT > 0
    // somFunc(...,INSTANCE_LAYER_COUNT,...);
#endif

//(II)

const char *g_pInstanceLayers[] = {"VK_LAYER_NV_optimus","VK_LAYER_LUNARG_standard_validation"};

int nNumberOfEllements = 0;

nNumberOfEllements = sizeof(g_pInstanceLayers) / sizeof(char*);
//or nNumberOfEllements = sizeof(g_pInstanceLayers) / sizeof(g_pInstanceLayers[0]);

printf("Number of ellements in the g_pInstanceLayers array is %d\n", nNumberOfEllements);

if(nNumberOfEllements)
{
    // somFunc(...,nNumberOfEllements,...);
}