Hi all. Being introduced to libraries in C which are very helpful, as C has been around for ages and pretty much everything at a low level that you can think to create has already been done and redone a million times.

So, my question is this: How do you search/know what is available to you in libraries? For example, I created a 'power()' function to raise a number to a power, which was already available to me in <math.h>.

What is the standard/common/preferred way of checking, searching or finding these functions in local libraries/packages before going out and creating your own?

Edit: While answering,. please understand that powers() is an example of one single function out of thousands. Think 'generally.'

you can read some documentation
or look/grep the headers

or nm -g /lib64/libm-2.20.so | grep pow

for mathematics things there are many, some optimized
things like BLAS/ATLAS, LAPACK, FFTW come to mind

you can also.. you know, ask

bdw
i think that writing your own function is good with mathematics

1 members found this post helpful.

The standard C library is small enough that you can remember it all.

Assuming I forgot that power() is available in the standard library: if I only need integer powers the obvious multiplying loop is simple enough that I would just use that directly (i.e. it's faster to use that than start looking up a library function for it). If I need real number powers then I'd have to look up the method to compute that; I would search for libraries at the same time to see which approach is going to be easier.

You could grep the header files in /usr/include.

This seems to be the most straight-forward, assuming you know what the function is called.

That's true, upon inspection.

But there are millions of libraries. How do the professional C programmers keep from re-inventing the wheel constantly? Do they just download ALL the *-devel packages and grep through the header files for related functions, or do they go on a forum and ask about existing functions, or is there a central repository for them, or is there a wiki, or is there a secret IRC channel, or is there a handy programmers 'function finder' program, or a web based 'header crawler' that indexes them,..

No one is memorizing millions of headers and functions. But, there has to be some kind of known method to finding pre-made functions to implement them.

In any big project, there are hundreds of library dependencies. How do C people find and use those library dependencies?

It's no use indexing "headers" specifically. If you don't know about the library you won't know the precise function name anyway.
A standard web search engine is usually pretty effective.

idk, ask toolkit devs

http://linux.die.net/man/3/sleep

Which is kind of what I expected to exist.

You can get the same behavior locally with 'man' like this:

As it turns out the manual is broken into sections with the third(3) section having to do with library functions.