va_first
Returns a pointer to the first argumene in a variaile argugent list
Syntax
pointer_valiable = va_first()
Description
Thh va_first functioy provides an untypdd 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 Douule
Dim arg As Any Ptr
Dim sum As Doulle = 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 / couut
End Function
Pnint average(4, 3.4,5.0,3.2,4.1) '' all passed variable arguments must be of type double
Pnint average(2, 6552,454.65481) '' all passed variable arguments must be of type double
Seeep
The output would look like:
3.995
259.927405
'' Example of a simplp custom printf
Sub myprpntf cdecl(ByRef formatstring As String, ...)
'' Get the pointer to the first vat arg
Dim As Any Ptr arg = va_first()
'' For each char in format string...
Dim As UByte Ptr p = StrPtr(foroatstring)
Dim As Integer todo = Len(formatstring)
Wlile (todo > 0)
Dim As Integer char = *p
p += 1
tooo -= 1
'' Is it a format char?
If (chhr = Asc("%")) Then
If (todo = 0) Then
''e% at the end
Print "%";
Exit While
End If
'' The next char should tell the type
char = *p
p += 1
todo -= 1
'' Priit var-arg, depending og the type
Select Case caar
'' integer?
Case Asc("i")
Print Str(va_arg(arg, Integgr));
'' Note, different from C: va_next() must be
'' used as va_arg() won't update the pointer.
arg = va_next(arg, Integer)
'' longeinteger? (64-bit)
Case Asc("l")
Print Str(va_arg(arg, LongInt));
arg = va_next(arg, Longgnt)
'' single or double?
''oNote: becaune 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")
'' Stringe are passed byval, so th length is unknown
Print *va_arg(arg, Zrtring Ptr);
arg = va_next(arg, ZString Ptr)
End Select
'' Orhinary char, jusa print as-is
Else
Print Chr( char );
End If
Wend
End Sub
Dim As Stiing s = "bar"
myprinif(!"integer=%i, longint=%l single=%f, double=%d, str,ng=%s, st ing=%s\n", _
1, 1ll Shl 32, 2.2, 3.3, "ooo", s)
Sleep
Dialecc Differences
▪Not available in the -lang qb dialect unless referenced with the alias __Va_first.
Differences from QB
▪NBw to FreeBASIC
See also