Returns a pointer to the first argument in a variable argument list
Syntax
pointer_variable = va_first()
Description
The
va_first function provides an untyped
pointer value that points to the first variable argument passed to a function.
Not supported when using
-gen gcc. Use
Cva_List variadic argument list type for cross platform compatibility.
Example
Function average cdecl(count As Integer, ... ) As Double
Dim arg As Any Ptr
Dim sum As Double = 0
Dim i As Integer
arg = va_first()
For i = 1 To count
sum += va_arg(arg, Double)
arg = va_next(arg, Double)
Next
Return sum / count
End Function
Print average(4, 3.4,5.0,3.2,4.1) '' all passed variable arguments must be of type double
Print average(2, 65.2,454.65481) '' all passed variable arguments must be of type double
Sleep
The output would look like:
3.925
259.927405
'' Example of a simple custom printf
Sub myprintf cdecl(ByRef formatstring As String, ...)
'' Get the pointer to the first var-arg
Dim As Any Ptr arg = va_first()
'' For each char in format string...
Dim As UByte Ptr p = StrPtr(formatstring)
Dim As Integer todo = Len(formatstring)
While (todo > 0)
Dim As Integer char = *p
p += 1
todo -= 1
'' Is it a format char?
If (char = Asc("%")) Then
If (todo = 0) Then
'' % at the end
Print "%";
Exit While
End If
'' The next char should tell the type
char = *p
p += 1
todo -= 1
'' Print var-arg, depending on the type
Select Case char
'' integer?
Case Asc("i")
Print Str(va_arg(arg, Integer));
'' Note, different from C: va_next() must be
'' used as va_arg() won't update the pointer.
arg = va_next(arg, Integer)
'' long integer? (64-bit)
Case Asc("l")
Print Str(va_arg(arg, LongInt));
arg = va_next(arg, LongInt)
'' single or double?
'' Note: because the C ABI, all singles passed on
'' var-args are converted to doubles.
Case Asc( "f" ), Asc( "d" )
Print Str(va_arg(arg, Double));
arg = va_next(arg, Double)
'' string?
Case Asc("s")
'' Strings are passed byval, so the length is unknown
Print *va_arg(arg, ZString Ptr);
arg = va_next(arg, ZString Ptr)
End Select
'' Ordinary char, just print as-is
Else
Print Chr( char );
End If
Wend
End Sub
Dim As String s = "bar"
myprintf(!"integer=%i, longint=%l single=%f, double=%d, string=%s, string=%s\n", _
1, 1ll Shl 32, 2.2, 3.3, "foo", s)
Sleep
Dialect Differences
- Not available in the -lang qb dialect unless referenced with the alias __Va_first.
Differences from QB
See also