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As per my understanding, C libraries must be distributed along with compilers. For example, GCC must be distributing it's own C library and Forte must be distributing it's own C library. Is my understanding correct?

But, can a user library compiled with GCC work with Forte C library? If both the C libraries are present in a system, which one will get invoked during run time?

Also, if an application is linking to multiple libraries some compiled with GCC and some with Forte, will libraries compiled with GCC automatically link to the GCC C library and will it behave likewise for Forte.

Jonathan Leffler
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Jay
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6 Answers6

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GCC comes with libgcc which includes helper functions to do things like long division (or even simpler things like multiplication on CPUs with no multiply instruction). It does not require a specific libc implementation. FreeBSD uses a BSD derived one, glibc is very popular on Linux and there are special ones for embedded systems like avr-libc.

Systems can have many libraries installed (libc and other) and the rules for selecting them vary by OS. If you link statically it's entirely determined at compile time. If you link dynamically there are versioning and path rules which come into play. Generally you cannot mix and match at runtime because of bits of the library (from headers) that got compiled into the executable.

The compile products of two compilers should be compatible if they both follow the ABI for the platform. That's the purpose of defining specific register and calling conventions.

Ben Jackson
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    That said, if I were to download or purchase a compiler, I'd feel cheated if it didn't at the very least come with some sort of libc, even if I end up choosing another! – Arafangion May 18 '11 at 06:59
  • As I said, GCC doesn't "come with" a libc. You also can't link programs with it: It's a compiler. A *build environment* includes a compiler, utilities (eg gnu binutils), headers, libraries, etc. – Ben Jackson May 18 '11 at 07:37
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As far as Solaris is concerned, you assumption is incorrect. Being the interface between the kernel and the userland, the standard C library is provided with the operating system. That means whatever C compiler you use (Forte/studio or gcc), the same libc is always used. In any case, the rare ports of the Gnu standard C library (glibc) to Solaris are quite limited and probably lacking too much features to be usable. http://csclub.uwaterloo.ca/~dtbartle/opensolaris/

jlliagre
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None of the other answers (yet) mentions an important feature that promotes interworking between compilers and libraries - the ABI or Application Binary Interface. On Unix-like machines, there is a well documented ABI, and the C compilers on the system all follow the ABI. This allows a great deal of mix'n'match. Normally, you use the system-provided C library, but you can use a replacement version provided with a compiler, or created separately. And normally, you can use a library compiled by one compiler with programs compiled by other compilers.

Sometimes, one compiler uses a runtime support library for some operations - perhaps 64-bit arithmetic routines on a 32-bit machine. If you use a library built with this compiler as part of a program built with another compiler, you may need to link this library. However, I've not seen that as a problem for a long time - with pure C.

Linking C++ is a different matter. There isn't the same degree of interworking between different C++ compilers - they disagree on details of class layout (vtables, etc) and on how exception handling is done, and so on. You have to work harder to create libraries built with one C++ compiler that can be used by others.

Jonathan Leffler
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Only few things of the C library are mandatory in the sense that they are not needed for a freestanding environment. It only has to provide what is necessary for the headers 

<float.h>, <iso646.h>, <limits.h>, <stdarg.h>, <stdbool.h>, <stddef.h>, and <stdint.h>

These usually don't implement a lot of functions that must be provided.

The other type of environments are called "hosted" environments. As the name indicated they suppose that there is some entity that "hosts" the running program, usually the OS. So usually the C library is provided by that "hosting environment", but as Ben said, on different systems there may even be alternative implementations.

Jens Gustedt
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Forte? That's really old.

The preferred compilers and developer tools for Solaris are all contained in Oracle Solaris Studio. C/C++/Fortran with a debugger, performance analyzer, and IDE based on NetBeans, and lots of libraries.

http://www.oracle.com/technetwork/server-storage/solarisstudio/index.html

It's (still) free, too.

rchrd
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I think there a is a bit of confusion about terms: a library is NOT DLL's or .so: in the real sense of programming languages, Libraries are compiled code the LINKER will merge with our binary (.o). So the linker (or the compiler via some directives...) can manage them, but OS can't, simply is NOT a concept related to OS.

We are used to think OSes are written in C and we can rebuild the OS using gcc/libraries or similar, but C is NOT linux / unix.

We can also have an OS written in Pascal (Mac OS was in this manner many years ago..) AND use libraries with our favorite C compiler, OR have an OS written in ASM (even if not all, as in first Windows version), but we must have C libraries to build an exe.

ingconti
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