Objectvie-C 两个字节 转换成整数

1.整数到转换成4个字节
int length=1491449719;
message[0] = length & 0xFF;
message[1] = (length >> 8) & 0xFF;
message[2] = (length >> 16) & 0xFF;
message[3] = (length >> 24) & 0xFF;

2.四个字节转换成整数
int len = message[0] | (message[1] << 8) | (message[2] << 16) | (message[3] << 24);

两个字节，情况下

1.整数到转换成2个字节
int year=1980;
message[0] = year & 0xFF;
message[1] = (year >> 8) & 0xFF;

2.四个字节转换成整数
int len = message[0] | (message[1] << 8);