fix last warnings in larson

examples/larson.c

@@ -19,6 +19,8 @@
  * random seed:    1
  */
 
+#define _XOPEN_SOURCE 500
+
 #include <pthread.h>
 #include <stdio.h>
 #include <sys/time.h>
@@ -158,9 +160,8 @@ static void * exercise_heap( void *pinput) {
 
         volatile char * chptr = ((char *) pdea->array[victim]);
         *chptr++ = 'a';
-        volatile char ch = *((char *) pdea->array[victim]);
-        ch = 'b';
-
+        volatile char ch __attribute__((unused)) = *((char *) pdea->array[victim]);
+        *chptr = 'b';
 
         if( stopflag ) break;
     }
@@ -201,7 +202,7 @@ static void runthreads(long sleep_cnt, int min_threads, int max_threads, int chp
     QueryPerformanceFrequency( &ticks_per_sec );
 
     pdea = &de_area[0];
-    memset(&de_area[0], 0, sizeof(thread_data));	
+    memset(pdea, 0, sizeof(thread_data));	
 
     prevthreads = 0 ;
     for(num_threads=min_threads; num_threads <= max_threads; num_threads++) {