Ada Programming, Libraries, Interfaces

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The Interfaces package helps in interfacing with other programming languages. Ada is one of the few languages where interfacing with other languages is part of the language standard. The language standard defines the interfaces for C, Cobol and Fortran. Of course any implementation might define further interfaces — GNAT, for example, defines an interface to C++.

Interfacing with other languages is actually provided by pragma Export,

• pragma Import and pragma Convention.

In Ada 2012 these clauses have an alternate form using "with" in place of "pragma."

Example

As an example, here is a complete program that queries the terminfo (terminal information) database on Unix systems to get the dimensions of the current terminal window. It interfaces with C language functions in the ncurses package, so it must be linked with ncurses (e.g. with the -lncurses switch) when it is compiled.

with Ada.Text_IO;
with Interfaces.C;
with Interfaces.C.Pointers;
with Interfaces.C.Strings;

procedure ctest is
use Interfaces.C;

type int_array is array (size_t range <>) of aliased int with Pack;

package Int_Pointers is new Pointers (
Index => size_t,
Element => int,
Element_Array => int_array,
Default_Terminator => 0
);

-- int setupterm (char *term, int fildes, int *errret);
function Get_Terminal_Data (
terminal  : Interfaces.C.Strings.chars_ptr;
file_descriptor  : int;
error_code_pointer : Int_Pointers.Pointer
) return int
with Import => True, Convention => C, External_Name => "setupterm";

-- int tigetnum (char *name);
function Get_Numeric_Value (name : Interfaces.C.Strings.chars_ptr) return int
with Import => True, Convention => C, External_Name => "tigetnum";

function Format (value : int) return String is
result : String := int'Image (value);
begin
return (if result(1) = ' ' then result(2..result'Last) else result);
end Format;

error_code  : aliased int;
error_code_pointer : Int_Pointers.Pointer := error_code'Access;

begin
if Get_Terminal_Data (Interfaces.C.Strings.Null_Ptr, 1, error_code_pointer) = 0 then
Ada.Text_IO.Put_Line (
"Window size: " &
Format (Get_Numeric_Value (Interfaces.C.Strings.New_String ("cols"))) & "x" &
Format (Get_Numeric_Value (Interfaces.C.Strings.New_String ("lines")))
);
else
Ada.Text_IO.Put_Line ("Can't access terminal data");
end if;
end ctest;

Child Packages

Interfaces.C
Interfaces.C.Extensions (GNAT)

• Interfaces.C.Pointers
• Interfaces.C.Streams (GNAT)
• Interfaces.C.Strings
• Interfaces.CPP (GNAT)
• Interfaces.COBOL
• Interfaces.Fortran
• Interfaces.OS2Lib (GNAT, OS/2)

Interfaces.OS2Lib.Errors (GNAT, OS/2)

• Interfaces.OS2Lib.Synchronization (GNAT, OS/2)
• Interfaces.OS2Lib.Threads (GNAT, OS/2)
• Interfaces.Packed_Decimal (GNAT)
• Interfaces.VxWorks (GNAT, VxWorks)

Interfaces.VxWorks.IO (GNAT, VxWorks)

See also

Wikibook

• Ada Programming
• Ada Programming/Libraries
• Ada Programming/Libraries/Standard
• Ada Programming/Libraries/Ada
• Ada Programming/Libraries/System

Ada 95

• Annex B Interface to Other Languages (Annotated)
• B.2 The Package Interfaces (Annotated)

Ada 2005

• Annex B Interface to Other Languages (Annotated)
• B.2 The Package Interfaces (Annotated)

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