一個自訂struct型態的變數，若想要轉換為unsigned，直接使用cast，gcc(version 4.4.3)編譯會回報錯誤。

例如：

struct _test {
unsigned hour : 5;
unsigned minute : 6;
};

struct _test var = {5, 6}
printf("var = %x\n", (unsigned)var);

error: aggregate value used where an integer was expected

解決方法是，改為

printf("var = %x\n", *(unsigned *)&var);