... (Ellipsis)


Used in place of procedure parameter to pass a variable number of arguments, or as the upper bound in an array declaration to denote that the number of elements will be determined by the initializer.

Syntax:
declare { sub | function } proc_name cdecl ( param_list, ... ) { | [ Byref ] As return_type }

#define identifier( [ parameters, ] variadic_parameter... ) body

dim array_symbol ([lbound to] ...) [as datatype] => { expression_list }

Description:
Variadic Procedures

The ellipsis (three dots, ...) is used in procedure declarations and definitions to indicate a variable argument list.

A first argument (at least) must always be specified and the procedure must be called with the C calling convention cdecl.

In the procedure body, cva_list data type, and cva_arg marco can be used to expand the ellipsis parameter (...) to obtain the values of the arguments passed to the variadic procedure. The argument list, once initialized with cva_start or copied with cva_copy, can be passed to another procedure taking a cva_list parameter.

On some targets, for backwards compatibility, va_first, va_arg and va_next can still be used to handle the variable arguments.

Only numeric types and pointers are supported as variable arguments (all bytes and shorts passed on variable arguments are implicitly converted to integers, all singles passed on variable arguments are implicitly converted to doubles). Strings can be passed, in which case a Zstring Ptr to the string data is taken.

A variadic procedure name can never be overloaded.

Variadic Macros

Using an ellipsis behind the last parameter in a #define or #macro declaration allows creation of a variadic macro. This means it is possible to pass any number of arguments to the variadic_parameter, which can be used in the body as if it was a normal macro parameter. The variadic_parameter will expand to the full list of arguments passed to it, including commas, and can also be completely empty.

Array Upper Bound

Using an ellipsis in place of the upper bound in an array declaration causes the upper bound to be set according to the data that appears in the expression_list. When the ellipsis is used in this manner, an initializer must appear, and cannot be Any.


Examples:
Declare Function foo CDecl (x As Integer, ...) As Integer


Dim As Integer myarray(0 To ...) = {0, 1, 2, 3}
Print LBound(myarray), UBound(myarray)   '' 0, 3


'' Using a variadic macro to wrap a variadic function
#include "crt.bi"
#define eprintf(Format, args...) fprintf(stderr, Format, args)
eprintf(!"Hello from printf: %i %s %i\n", 5, "test", 123)

'' LISP-like accessors allowing to modify comma-separated lists
#define car(a, b...) a
#define cdr(a, b...) b


Differences from QB:
See also:
Back to Procedures
Back to Variable Argument list
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