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import "C"
Calling C From Go
27 Mar 2013
Tags: go c

Miki Tebeka
Technical Lead, Adconion
miki.tebeka@gmail.com
http://mikitebeka.com
@tebeka

* Why C?

After all we have Go, which is much better :)

However, there is a *huge* volume of software written in C.
We'd like to re-use it and not re-write it.

* import "C" (A.K.A cgo)

Provides an easy bridge between Go and C

The Downside
- Hard to find docs (see reference slide)
- Pay attention to memory leaks
- Compilation time grows
- For C++ you need `extern`"C"` and C like wrapper
- Users need C compilers and libraries installed
- Cross compilation [[https://code.google.com/p/go/issues/detail?id=4714][does not work]]

Note that are other options (such as [[http://www.swig.org/][swig]])



* Minimal Example

.play import-c/sqrt.go


* Strings

.play import-c/str.go

* Ahhhhhh!

.image import-c/picard1.jpg 400 600

* Strings

.play import-c/str2.go

* But ...

.image import-c/picard2.jpg 400 600

* Strings

.play import-c/str3.go

* Structs

.play import-c/struct.go

* Calling Go from C

`callback.c`

.code import-c/callback/callback.c

`callback.h`

.code import-c/callback/callback.h

* Calling Go from C

`callback.go`

.code import-c/callback/callback.go

* Go Style Errors

.play import-c/err.go

* Case Study - snowball

- [[https://bitbucket.org/tebeka/snowball]]
- Port of [[http://snowball.tartarus.org/][snowball]] stemmer to Go
- Had to flatten directories and rewrite #include
- Wasn't that painful

.play import-c/stem.go

* snowball - imports and definition

.code import-c/snowball.go  /START_IMPORT/,/END_IMPORT/

* snowball - New and free

.code import-c/snowball.go  /START_NEW/,/END_NEW/


* snowball - Stem

snowball uses `sb_symbol*` for string

.code import-c/snowball.go  /START_STEM/,/END_STEM/

* snowball - List

The list of languages is a `static`char*` array with a `NULL` sentinal

.code import-c/snowball.go  /START_LIST/,/END_LIST/


* References

- [[http://golang.org/cmd/cgo/][cgo docs]]
- [[http://golang.org/doc/articles/c_go_cgo.html][C? Go? Cgo!]]
- [[http://golang.org/misc/cgo/][cgo examples]]
- [[https://code.google.com/p/go-wiki/wiki/cgo][cgo wiki]]
- [[http://stackoverflow.com/search?q=%5Bgo%5D+cgo][StackOverflow]]

* Lets Hack!

.image import-c/real-programmers.jpg 400 600