Stdcall

Stdcall is a calling convention used primarily on 32-bit Windows systems to define how functions receive arguments, return values, and manage the call stack. It is widely used by the Windows API and by COM interface methods written in C or C++ on 32-bit platforms.

In stdcall, arguments are pushed onto the stack from right to left. The called function is responsible for cleaning up the stack before returning, typically via a ret N instruction that removes the total size of the arguments. The return value, if any, is placed in the EAX register. The ABI also defines which registers must be preserved by the callee; on 32-bit Windows, callee-saved registers include EBX, ESI, EDI, and EBP, while EAX, ECX, and EDX are caller-saved.

Symbol naming on some linkers and toolchains uses a decorated form, with the function name followed by @N to indicate the number of argument bytes, e.g., FunctionName@8. In C or C++, the convention is exposed by the __stdcall keyword or macro. It is also available in languages such as Pascal and Delphi.

On 64-bit Windows, stdcall is not used as a separate convention; the platform uses the Microsoft x64 calling convention, which does not employ name decoration and has fixed register rules. 32-bit code may interoperate with 64-bit code using other interop mechanisms, but stdcall-specific decoration and stack-cleanup semantics apply only to 32-bit environments.

See also: cdecl, fastcall, thiscall, Microsoft x64 calling convention.