我应该如何读取C中的逆序字节？

Question

I need to read in unsigned char * bytes which are in reverse order to the native order. At the moment I have lots of little routines along the following lines:

uint8_t * bytes;
uint32_t r;
bytes = pt;
r = (((((bytes[0] << 8) + bytes[1]) << 8) + bytes[2]) << 8) + bytes[3];
pt += 4;
return r;

Is there a standard or portable way to do this kind of job, or do I have to hack up functions like this?

Answer 1

The socket library for your platform provides the following functions which do these conversions:

• ntohs - Network to Host Short (16-bit)
• htons - Host to Network Short (16-bit)
• ntohl - Network to Host Long (32-bit)
• htonl - Host to Network Long (32-bit)

To implement your code above, you can:

r = ntohl(*(uint32_t *)bytes);