Re: C/C++ calling convention

James Kanze <>
Thu, 26 Aug 2010 03:20:55 -0700 (PDT)
On Aug 26, 12:25 am, "BGB / cr88192" <> wrote:

"James Kanze" <> wrote in message
On Aug 25, 3:44 pm, Goran Pusic <> wrote:

On Aug 25, 4:18 pm, Stanis=B3aw Findeisen <> wrote=



Any compiler provides you with a way to specify what calling
convention you want from a list of calling conventions chosen by that
compiler (look for e.g. __cdecl).

On most machines, there is only one reasonable way to pass
arguments when calling a function, and most compilers do not
need or have extensions to specify many different calling
conventions---they use the standard ``extern "language"''.

well, if one excludes 32 bit Windows, where in practice 4 calling
conventions are commonly used:
cdecl; stdcall; fastcall; and thiscall (modified cdecl).

By "most machines", I meant most types of machines. Windows is
a bit of an exception, although even here, it's only really an
exception when using VC++, who decided not to use the standard
mechanism. (cdecl and stdcall resolve to ``extern "C"'' and
``extern "Pascal"'', I think. And thiscall is an extension of
cdecl, only relevant for ``extern "C++"''. The language also
allows a compiler to define something like ``extern "Fast"'',
although why one would use a slow call when a fast one is
available is beyond me.)

in most cases, fastcall can be ignored (it is almost never
used for external linkage AFAICT), and thiscall can simply be
regarded as a special case of cdecl.

this is a major reason for modifier tags like WINAPI and
similar: they wrap the calling convention keywords.

on 64-bit Windows, there is a single calling convention (Win64);
on 64-bit Linux and OSX, there is a single calling convention (AMD64);

As is the case under Solaris, HP/UX and AIX. And probably every
other system around.

on 32-bit Linux, in practice pretty much everyone just uses

On 32-bit Linux, I've never used anything.

IIRC, MS-DOS was a mess though, with many compilers doing
things differently, so code from one compiler would not
normally link correctly with code produced by another.

Yes and no. All of the C compilers I tried did the same thing.
All of the C++ compilers were different. But that's the case
almost universally today as well.

32-bit Windows mostly stabilized the calling convention and
object-file format mess (nearly everything is either cdecl or
stdcall, and uses COFF...).

Windows defines an ABI for C, I think (which it uses when
calling into system DLL's).

James Kanze

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