CVA_ARG
Macro to obtain the next argument from a variadic argument list object.
Syntax:
variable = cva_arg ( argument_list, datatype )
Parameters:
argument_list
cva_list data type variable to access for next value
datatype
The datatype of the next value in the variable argument list argument_list
Description:
The cva_arg macro allows the use of a variable number of arguments within a function:
- cva_arg returns the current argument in the list, argument_list, with an expected data type of datatype.
- Before first cva_arg use, argument_list must be initialized with the command cva_start or cva_copy.
- cva_arg automatically increments argument_list to the next argument within the list after obtaining the value of the current argument.
Examples:
'' Example of a simple custom printf
Sub myprintf CDecl(ByRef formatstring As String, ...)
Dim As cva_list args
'' Initialize the cva_list object to first var-arg
cva_start( args, formatstring )
'' 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(cva_arg(args, Integer));
'' long integer? (64-bit)
Case Asc("l")
Print Str(cva_arg(args, 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(cva_arg(args, Double));
'' string?
Case Asc("s")
'' Strings are passed byval, so the length is unknown
Print *cva_arg(args, ZString Ptr);
End Select
'' Ordinary char, just print as-is
Else
Print Chr( char );
End If
Wend
cva_end( args )
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)
Sub myprintf CDecl(ByRef formatstring As String, ...)
Dim As cva_list args
'' Initialize the cva_list object to first var-arg
cva_start( args, formatstring )
'' 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(cva_arg(args, Integer));
'' long integer? (64-bit)
Case Asc("l")
Print Str(cva_arg(args, 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(cva_arg(args, Double));
'' string?
Case Asc("s")
'' Strings are passed byval, so the length is unknown
Print *cva_arg(args, ZString Ptr);
End Select
'' Ordinary char, just print as-is
Else
Print Chr( char );
End If
Wend
cva_end( args )
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)
Version:
- Since fbc 1.07.0
Dialect Differences:
- Not available in the -lang qb dialect unless referenced with the alias __cva_arg.
Differences from QB:
- New to FreeBASIC
See also:
Back to Procedures
Back to Variable Argument list
