This is the default calling convention used when interfacing to C/C++ routines compiled with either gcc or Microsoft Visual C++.
C calling convention subprogram parameters are pushed on the
stack by the caller from right to left. The caller itself is in charge of
cleaning up the stack after the call. In addition, the name of a routine
C calling convention is mangled by adding a leading underscore.
The name to use on the Ada side when importing (or exporting) a routine
C calling convention is the name of the routine. For
instance the C function:
int get_val (long);
should be imported from Ada as follows:
function Get_Val (V : Interfaces.C.long) return Interfaces.C.int; pragma Import (C, Get_Val, External_Name => "get_val");
Note that in this particular case the
External_Name parameter could
have been omitted since, when missing, this parameter is taken to be the
name of the Ada entity in lower case. When the
is missing, as in the above example, this parameter is set to be the
External_Name with a leading underscore.
When importing a variable defined in C, you should always use the
calling convention unless the object containing the variable is part of a
DLL (in which case you should use the
DLL calling convention,
see DLL Calling Convention).