Nim stdarg

This is a Nim wrapper for the standard C header <stdarg.h>. One can use it to make variadic procedures that can be used from C/C++.

Standard C functions that take va_list (the list object, not "...") as arguments are also wrapped (those from <stdio.h> are in stdarg/io, and those from <wchar.h> in stdarg/wchar).

Example

import stdarg

proc sum(x: int): int {.varargs.} =
  var
    args {.noInit.}: VAList
    a: int
  args.init(x)
  result = x
  while true:
    args.next(a)
    if a == 0:
      break
    result += a

echo sum(1, 2, 3, 0)

To make a procedure that takes variable number of parameters, mark it as {.varargs.} and declare a variable of type VAList. After that, call init with the last parameter name to initialize it. Use next to store the next argument into a variable.

Note that {.varargs.} is a built-in pragma. It tells the compiler that the procedure is able to take more arguments.

Note

• This package is only useful when interacting with C/C++. The built-in varargs[T] should be used in other cases.

• For each VAList initialized with init(), va_end will be automatically invoked (and thus don't need to be called explicitly). For a VAList initialized with another method, va_end must be called once in the same proc as it initialized. However it don't need to be invoked if the list is never initialized.

References

• https://cplusplus.com/reference/cstdarg/
• https://cplusplus.com/reference/cstdio/
• https://cplusplus.com/reference/cwchar/
• https://en.cppreference.com/w/c/experimental/dynamic/asprintf