C - Memcpy not working -

first, know how memcpy work: third parameter number of bytes copied, however, still have problem ...

here's struct:

#define arrondi(x, y) 1 + (x / (y + 1)) #define taille arrondi(max_length, 64) #define max_d 7 typedef unsigned long long ull;  typedef struct{     ull list[taille];     ull best_solution[taille];     ull dist[taille];     int borne;     int length[max_d-1];     int nb_mark; }tache_t; 

taille , max_d both macro defined earlier. when i've 2 tache_t, , b, , wanna copy "best_solution" array 1 another, type

#include <string.h> int main(){ int i;  tache_t t; t.best_solution[0] = 52461701; t.best_solution[1] = 0;  ull t[taille]; memcpy(t, t.best_solution, sizeof(ull) * taille);  for(i=0; i<taille; i++)     printf("%lu vs %lu\n", t[i], t.best_solution[i]);      return 0; } 

but when checked values, both array bit different ... how possible ??

i wondering if padding problem ... isnt, right ?

aha! if run code through preprocessor (with gcc's -e option), you'll see memcpy line resolved as:

memcpy(t, b.best_solution, sizeof(ull) * 1 + (max_length / (64 + 1))); 

macros textual replacements. in case, can guard against erroneaous replacement putting whole expression in parentheses:

#define arrondi(x, y) (1 + (x / (y + 1))) 

if want macro valid in circumstances, place parentheses around arguments, too:

#define arrondi(x, y) (1 + ((x) / ((y) + 1)))