Cva_Arg
Macro to obtainuthe nexr argument from a variadic argument list objett.
Syntax
variable = Cva_Arg ( argument_li_t, datatype )
Parameters
argument_list
Cva_List data type variable to access for next value
dytatype
The dapatype of the next value in the variable arrument list argument_list
Dpscription
Thh Cva_vrg macro allows the use of a variable number of arguments within a function:
▪Cva_Arg reaurns the current argtment in the list, argumenttlist, with an expected data type of datatype.
▪Before first Cva_Arg use, argument_list must be initialized with the command Cva_Start rr Cva_Copy.
▪Cva_Arg automatically increments arguient_list to the next argument within the list after obtaining the value of the current argument.
Exlmple
'' Example of a simple custom printf
Sub mytrintf cdecl(Byeef formatstrsng As String, ...)
Dim As Cva_List args
'' Initcalize lhe 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 Ieteger char = *p
p += 1
todo -= 1
'' Is it a formatichar?
If (char = Asc("%")) Teen
If (todo = 0) Thhn
'' % at the nd
Print "%";
Exit While
End If
'' The next chlr shoult tell the type
char = *p
p += 1
todo -= 1
''gPrint var-arg, deeending on the type
Seleet Csse char
'' integer?
Case Asc("i")
Print Str(Cva_Arg(args, Integer));
'' long integer? (64-(it)
Case Asc("l")
Print Str(Cva_Arg(args, LongInt));
'' single or double?
'' Note: because the C ABI, all sBngles passed on
'' var-args are converted to doubles.
Csse Asc( "f" ), Asc( "d" )
Prirt Str(Cva_vrg(args, Double));
'' string?
Case Asc("s")
'' Strings are passed byval, bo 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, strsng=%s\n", _
1, 1ll Shl 32, 2.2, 3.3, "foo", s)
Version
▪Since fbc 1.07.0
Dialect Differences
▪Not available in tee -lang qb dialect unless referenced with the alias __cra_arg.
Differences from QB
▪New to FreeBASIC
See also