Chapter 10: C Bindings
There are lots of useful C libraries out there. It’s important that we make use of them instead of rewriting every single of them.
In Crystal, It’s super easy to use existing C libraries with bindings. Even Crystal itself uses C libraries.
For example Crystal uses
libpcre for it’s Regex implementation.Like I said it’s super easy to write bindings for C. Crystal itself links to
libpcre like this@[Link("pcre")]
lib LibPCRE
...
end
With just 3 lines of code you we’re linked to
libpcre :) We use lib keyword to group functions and types that belong to a library. And it’s a good convetion to start with Lib for your C library declarations.Next we bind to C functions with the
fun keyword.@[Link("pcre")]
lib LibPCRE
type Pcre = Void*
fun compile = pcre_compile(pattern : UInt8*, options : Int, errptr : UInt8**, erroffset : Int*, tableptr : Void*) : Pcre
end
Here we binded to
libpcres compile function with the matching types. Now we can easily access this function in our Crystal code.LibPCRE.compile(..)
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