Object-oriented Software in Ada 95

25 Mixed language programming
This chapter describes how code written in another language can be called from an Ada program. This
allows the Ada programmer to take advantage of the wealth of code previously written in other languages.
25.1 Linking to other code
The designers of Ada 95 realised that if the language was to prosper then it must co-exist in a world where code
was written in languages other than Ada. Ada provides mechanisms that allow code written in the programming
languages C, Fortran and COBOL to be directly called. Other languages such as C++ may also be called using the
C interface.
25.2 Selected types and functions from Interfaces.C
The following are a selection of types and functions from the package Interfaces.C. This Ada package
allows the calling of functions written in the C language. In particular mechanisms are provided to convert
between instance of Ada types and instances of C types.
25.2.1 Integer, character and floating point types
By using the following types an Ada variable or expression can be converted to a form compatible with the C
language.
Integer Types Char types Floating point types
Char
Wchar_T
Int
Short
Long
Size_T
C_Float
Double
Long_Double.
For example to pass the integer value Item as a parameter to a C function that expects a long double the
following expression can be used: Long_Double(Item).
25.2.2 C String type
The following declaration:
type Char_Array is Array (Size_T range ) of aliased Char;
is used to declare a C array of characters. In C an array of characters terminated by the null character is used to
represent a string. For example, the following will declare a string Name containing the text "Miranda" that
may be passed to a C function that requires a C string parameter.
Name : constant Char_Array := "Miranda" & nul;
Note:
25.2.3 Selected functions
The use of nul to represent the null character. Remember null is an Ada reserved word.
Character conversions:
© M A Smith - May not be reproduced without permission