This documentation is archived and is not being maintained.


Microsoft Specific

The __fastcall calling convention specifies that arguments to functions are to be passed in registers, when possible. The following list shows the implementation of this calling convention.

Element Implementation
Argument-passing order The first two DWORD or smaller arguments are passed in ECX and EDX registers; all other arguments are passed right to left.
Stack-maintenance responsibility Called function pops the arguments from the stack.
Name-decoration convention At sign (@) is prefixed to names; an at sign followed by the number of bytes (in decimal) in the parameter list is suffixed to names.
Case-translation convention No case translation performed.
Note   Future compiler versions may use different registers to store parameters.

Using the /Gr compiler option causes each function in the module to compile as fastcall unless the function is declared with a conflicting attribute, or the name of the function is main.


In the following example, the function named DeleteAggrWrapper is passed arguments in registers:

// Example of the __fastcall keyword
#define FASTCALL    __fastcall
void FASTCALL DeleteAggrWrapper(void* pWrapper);
// Example of the __ fastcall keyword on function pointer
typedef BOOL (__fastcall *funcname_ptr)(void * arg1, const char * arg2, DWORD flags, ...);

END Microsoft Specific

See Also

Argument Passing and Naming Conventions | C++ Keywords