Question

I’m writing a client and server program with Linux socket programming. I’m confused about something. Although sizeof(char) is guaranteed to be 1, I know the real size of char may be different in different computer. It may be 8bits,16bits or some other size. The problem is that what if client and server have different size of char. For example client char size is 8bits and server char size is 16bits. Client call write(socket_fd, *c, sizeof(char)) and Server call read(socket_fd, *c, sizeof(char)). Does Client sends 8bits and Server wants to receive 16bits? If it is true, what will happen?

Another question: Is it good for me to pass text between client and server because I don’t need to consider the big endian and little endian problem?

Thanks in advance.

Answer 1

@Basile is right. A char is always eight bits in linux. I found this in the book Linux Kernel Development. This book also states some other rules:

1. Although there is no rule that the int type be 32 bits, it is in Linux on all currently supported architectures.

2. The same goes for the short type, which is 16 bits on all current architectures, although no rule explicitly decrees that.

3. Never assume the size of a pointer or a long, which can be either 32 or 64 bits on the currently supported machines in Linux.

4. Because the size of a long varies on different architectures, never assume that sizeof(int) is equal to sizeof(long).

5. Likewise, do not assume that a pointer and an int are the same size.

For the choice of pass by binary data or text data through the network, the book UNIX Network Programming Volume1 gives the two solutions:

1. Pass all numeric data as text strings.

2. Explicitly define the binary formats of the supported datatypes (number of bits, big- or little-endian) and pass all data between the client and server in this format. RPC packages normally use this technique. RFC 1832 [Srinivasan 1995] describes the External Data Representation (XDR) standard that is used with the Sun RPC package.