Object-oriented Software in Ada 95

362 Mixed language programming
function To_C (Item : in Character) return Char;
function To_Ada (Item : in Char ) return Character;
String conversions:
function To_C ( Item : in String;
Append_Nul:in Boolean := True )
return char_array;
function To_Ada ( Item: in char_array;
Trim_Nul : in Boolean := True )
return String;
25.3 An Ada program calling a C function
The following Ada program calls the C function triple. The C function triple returns as an integer value triple
the integer value passed to it. Firstly an interface function Triple is constructed that calls the C function
triple.
with Interfaces.C;
use Interfaces.C;
function Triple( N:in Integer ) return Integer is
function C_Triple(N:in Int) return Int;
pragma Import (C, C_Triple, "c_triple");
begin
return Integer( C_Triple( Int(N) ) );
end Triple;
Note: The use of the type defined in Interfaces.C s:
Int
Represents a C int
Integer The Ada integer type.
In the Ada interface function the pragma import is used to request the compiler to link to an externally
written procedure or function. In this case the function c_triple written in C.
This interface function triple is then called from a simple test program.
with Ada.Text_Io, Ada.Integer_Text_Io, Triple;
use Ada.Text_Io, Ada.Integer_Text_Io;
procedure Main is
begin
Put("3 Tripled is "); Put( Triple(3) ); New_Line;
end Main;
The implementation of the function c_triple in C is:
int c_triple( int n ) /* function to triple argument */
{
return n + n + n;
}
The above code when compiled and linked will produce the following output.
© M A Smith - May not be reproduced without permission