[fpc-pascal] Calling C functions from FPC

Jonas Maebe jonas.maebe at elis.ugent.be
Mon Jan 26 08:20:29 CET 2009

On 26 Jan 2009, at 01:24, Ken G. Brown wrote:

> On MacOS X 10.5.6 Intel targeting 10.3.9 PPC:
> What are the gotchas with respect to calling C functions from FPC?

Mark the external C functions you import in your Pascal code as  
"cdecl", e.g.

procedure cTest; cdecl; external;

> What other issues might I have to watch out for?

Make sure that the types in your Pascal and C code match. The easiest  
is to use the ctypes unit. Then you can use the common C-types by  
prefixing them with "c" (e.g., cint, clong, clonglong, cuint, culong,  
culonglong, cfloat, ...). And don't try to free pointers allocated in  
the C code in Pascal code and vice versa.


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