在數組c中移位2字節

Question

所以我一直在嘗試從一個數組中移位2個字節，我有時候會以很好的值結束，但並不是所有的時間。所以這裏是一個例子。

char buffer[2]; //current character buffer to store the bytes 
    unsigned int number; //the unsigned int to store values 

    number = buffer[0] << 8 | buffer[1]; //bitshifting 
    printf("%02x ", number); 

我似乎在某些情況下得到了這個。

ffffffbc // the bc seems to be correct however the f's are not 

Answer 1

這是因爲char晉升爲整數，其符號位，則需要促進完成之前轉換爲unsigned值。所以 number = buffer[0] << 8 | buffer[1];應該是

number = (unsigned char)buffer[0] << 8U | (unsigned char)buffer[1];