Question

I had been doing some file IO in a project i am currently working on and so far I have been reading in a whole block of data using the following fast and convenient method:

struct Header { ... };
class Data { ... };
// note that I have not used compiler directives to pack/align/order bytes
// partly because I don't know how to.

Header _header;
Data _data;
std::ifstream fin(filename);
fin.read((char*)&_header, sizeof(Header));
fin.read((char*)&_data, sizeof(Data));
fin.close();

My question is whether it is ok to assume the bytes are aligned and order in the same way for every compiler and every different computer?

For example, if I take the Header struct and compile a client program, on linux, and a server program on windows. Are the bytes in the same order such that there will be no issues receiving and sending both ways?

Answer 1

No, that’s not guaranteed at all. There is a specific network byte order and as far as I know, both WinAPI and POSIX provide local to network translation functions. In addition, the alignment you can control with compiler directives. But you have to explicitly take care of both of these things.