Question

I am in the middle of reading The Linux Programming Interface and Linux programming by examples. Both are very good books and explain Linux API very well. But quite often I find myself thinking that in real world projects I would prefer C++ standard library, Boost or some other good C++ library (there are many well written and portable C++ libs) over C API whenever possible. This naturally bags a question – why do I need to use Linux API directly when good C++ compiler and libs (Boost, TBB and etc) are available on target platforms? I guess the same could be said about Windows API too, but I don’t know much about Windows system programing.

Answer 1

This is not new to C++. In C, there have been two ways to open files for a long, long time:

// Only on POSIX
int fdes = open("file.txt", O_RDONLY);

Or:

// Any hosted C environment, POSIX or otherwise
FILE *fp = fopen("file.txt", "rb");

So why would anyone ever use the POSIX-specific version? The answer is simple — there are a large number of system calls which work with POSIX file descriptors. For example, select. You can also make things other than files, like pipes and sockets, and you can pass them to other processes. There is a long tradition of using POSIX file descriptors, and we have a large number of books and references on how to do network programming with them.

So the trade-off is between the portable version and the powerful version. It always has been.

The other half of this is that time you work with files on Linux you are working with the POSIX interface. Libraries just hide it from you. Boost uses it, the C runtime uses it, the JRE uses it, and GHC uses it. Many (most?) language runtimes are written in C, and direct access to the system calls is preferred.