Does a C++ standard library have to be written in C or assembly?

Question

Is it possible to write the complete C++ standard library (including STL of course, but self-contained, only internal dependencies) using only C++? I would imagine containers and <cstdlib> functionality would be doable in terms of chars, bitshifts, and for loops and other byte fancy things, but stuff like exceptions and perhaps std::cout and std::cin seem hard to me without a dependency to begin with. Let's say there is a set of OS functions available, that are completely implemented in assembly (to avoid any C contamination).

I'm assuming the compiler understands everything from classes and virtual functions to templates and function overloading, these are language level things and have no place in a library IMHO.

If this has been asked before or is a trivially stupid question, please forgive me. I'm not trying to start a C<->C++ war here, just trying to figure out the limitations of implementing a beast such as the Standard library...

Thanks!

Answer 1

The only piece of C++ that needs assembly is the exception handling. I suppose that it might be doable in C++ if there exist libraries to handle the necessary register and stack management.

Of course, those libraries would then include assembly. There just isn't any other way to do direct register management.

Answer 2

First thing, it doesn't matter if it's C, C++, or D. Any compilable programming language at the end gives you (mostly) the same assembly object file.

Second thing, STL is written in C++, you cannot write C++ library in C or any other language (well, you can but I assume, that we're talking on reasonable solutions). You cannot implement STL containers in C, because the're strongly use templates.

GCC generate really nice output in asm for exceptions now. I recommend to read about C++ ABI (if you're interested in it).

C++ compiler understands all C++ specific features really nice nowadays. Thanks to really advanced code analysis and optimizations, it's able to produce fast executables (see first paragraph).

I hope that I've at least partly answered your question.

Answer 3

The STL is very heavily reliant on #includeed header files. Those pretty much have to be C++.

Anything that isn't in one of those header files though could in theory be implemented in C, Ada, Assembly, or the other systems-programming language of your choice. However, you'd probably have to be maintaining two interfaces if you don't make at least the top layer C++.

Answer 4

Since pretty much anything written in C can be rewritten fairly easily in C++, you're asking whether assembly code is needed, and the answer is generally no.

Unless we're talking about embedded programming, operating systems have all the necessary file and I/O functionality available through system calls, usually (nowadays) in C format. The library needs to call them, likely through extern "C"{ ... } declarations. The operating system functions are not considered part of the C++ library, and typically aren't exact matches to anything defined in the C++ Standard.

To implement a C++ standard library, you would need to be familiar with the language itself, know the OS calls you're going to use, and have the algorithms you're going to use. At that point, it's a relatively straightforward matter of writing the software.