#Caché Native Access (CNA)#

CNA provides an interface for using native C-compatible shared libraries without anything but Caché ObjectScript code. CNA is a wrapper for libffi. CNA consists of native library (libcna) and Caché class (CNA.CNA).

##Installation##

###Linux###

• Build libfii: make libffi. If 'make' says that GLOBALS_HOME is undefined, then define it:

 export GLOBALS_HOME='path to Caché root directory'

• Build libcna: make
• Done! File we are looking for — libcna.so. After all you need to import "cna.xml" in any Caché namespace:

 do $system.OBJ.Load("path to cna.xml", "c")

###Windows###

For Windows-based systems you can try to do the same as for Linux (for building you may use mingw32 or mingw32-w64). Or you can just download binary files. Note: types (32-bit or 64-bit) of libcna, current Caché installation and external libraries must be equal.

##Runnning tests##

If you want to check if CNA works correctly on your system you may run the unit-tests. You will need native library with test functions 'libtest'. If you build CNA by yourself, it is already in the right place. If no — it must be placed in directory cna/tests/. Than you should set ^UnitTestRoot global to the right value and run the tests.

 set ^UnitTestRoot="path to 'cna/tests/' directory"  
 do ##class(%UnitTest.Manager).RunTest()

##Simple example##

Let's try to call strlen function from C standard library. In Windows it should be located in C:\Windows\System32\msvcrt.dll. In Linux — /usr/lib/libc.so. strlen returns the length of the string:

 size_t strlen ( const char * str );

Let's see what you need to do to call it from Caché:

 set cna = ##class(CNA.CNA).%New("path to libcna"); Creates object of CNA.CNA class.
 do  cna.LoadLibrary("path to libc")              ; Loads C standard library in CNA

 set string = cna.ConvertStringToPointer("Hello") ; Converts the string into char array, and saves pointer to the first element
                                                  ; That's how string are stored in C

 set argTypes = $lb(cna.#POINTER)                 ; Creates list of CNA.CNA pararmeters. Each parameter stands for the type of the function argument

 set result = cna.CallFunction("strlen",          ; Passes the name of the function,
                                cna.#SIZET,       ; type of return value,
                                argTypes,         ; list of argument types,
                                string)           ; and comma-separated arguments 

 write result, !                                  ; Writes the result (it should be 5)
 do cna.FreeLibrary()                             ; Frees the library