Why in Linux compiler we have to give additional arguments while compiling and running C programs?

I have implemented semaphores in Linux last year. But for that I have to use -lpthread.

Now while implementing log10() function in C, I surfed the INTERNET and I saw that I have to use -lm.

I want to know why these kind of command line arguments are necessary in Linux.And Does this rule is compiler oriented?

(In windows Turboc compiler, I never used these kind of 开发者_如何学JAVAarguments.)

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You are instructing the compiler to look for certain libraries and use them to try and produce a final object file.

When you were doing your threading code, you used threading primitives. These threading primitives are implemented in a library called pthread, -lpthread tells the linker to use the library pthread, without providing this switch the compiler will not be able to produce a valid object file as it is missing threading code implementation.

On the file system the libraries can be found in /usr/lib and lib (among others) when you look in these directories you will see files start with the lib prefix. for example libpthreadxxxxxx. You will have to do your own research to figure out what the xxxx means.

The development cycle using unix style tools is very granular on the surface, when you use heavyweight IDE's (read: visual studiio for C++), the IDE implicetly links against loads of standard libraries, so often you do not need to supply the name of the libraries you will commonly use. However, when you start doing more advanced programming you will probably have to install and configure your IDE to use external code libraries. If you were to use threading primitives in visual studio, you most likely will not have to provide the compiler with information on where to look for threading primitives, Microsoft considers this a common library and every new project will implicitly link against it.

A little discussion on GCC

GCC is a very diverse compiler producing code for various different usage scenarios. As such they try to be neutral and do not make assumptions. For example pthread is a particular threading primitives implementation. However, even through now on Linux at least it is the defacto standard, it is not the only one. Other Unix implementation have had different implementation. When such choices exist it is not fair for the compiler developers to implicitly link against libraries. They do however implicitly link against standard libraries; for example G++ is just a wrapper command to the internal compiler code, it is a C++ front-end so it implicitly links against an implementation of the C++ standard library. Similarly the C front end links against a the standard C library.

People often do not want to use certain standard library implementation, and instead they might want to use another implementation, in such cases you have to explicetly inform the compiler to use an implementation that you provide. Such use cases are very granular and are surface level issues with G++. In visual studio, you would have to tinker a lot to make such changes generally, since it is not an anticipated use-case anymore.

wikipedia will provide you with more information.

Edit: I'll fix the spelling and Grammatical issues later :D

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The option -l indicates to gcc what libraries must be used for linking. -lpthread stands for "use the pthread library", and -lm stands for "use the m library" which is the math library. These commands are relative to gcc, not linux.

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Because by default, gcc only links the C library (libc), which contains the well-known functions printf, scanf, and many more.

log10 exists in a different library called libm, and thus you need to explictly tell gcc to link that library, with -lm. The same logic applies for -lpthread.

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This is purely a backwards, harmful practice. Separating parts of the standard library into separate .so files does nothing but increase load time and memory usage. Good luck getting anyone to change it though... Just accept that you have to do it (and that POSIX specifically allows, but does not require, that an implementation require -lm for using the math functions and -lpthread for using threads, etc.) and move on to more important things.

Or, go pester Drepper about it on the glibc bug tracker/mailing list. He won't change his mind, but if you enjoy flamewars you can get some kicks...