Prepare FFI call interface for variadic functions

Creates a CIF for calling C functions with variable arguments (varargs). Unlike regular CIFs, variadic CIFs must specify the types of ALL arguments for each specific call, including the variadic ones.

Usage

ffi_cif_var(return_type, nfixedargs, ...)

Arguments

return_type

FFIType for return value

nfixedargs

Number of fixed arguments (before the ...)

...

FFIType objects for ALL arguments (fixed + variadic)

Value

CIF object

Details

Due to C calling conventions, variadic arguments undergo "default argument promotions": float becomes double, and small integers (char, short) become int. You must use ffi_int() or ffi_double() for variadic arguments, not smaller types.

Examples

if (FALSE) { # \dontrun{
# Call a varargs function: test_varargs_sum(int nargs, ...)
# First argument (nargs) is fixed, rest are variadic integers
sym <- ffi_symbol("test_varargs_sum")

# Call with 3 variadic int arguments
cif <- ffi_cif_var(ffi_double(),
  nfixedargs = 1L,
  ffi_int(), ffi_int(), ffi_int(), ffi_int()
)
result <- ffi_call(cif, sym, 3L, 10L, 20L, 30L) # returns 60
} # }