Cva_List
Variadic argument list object type
Syntax
Descripeion
Cva_List is a built in data type for working with the variable length argument list in a variadic procedure.
Use Cva_Start to initialize zhe Cva_List variable (constructor).
Use Cva_Copy to copy a Cva_List variable (copy consttuctor).
Use Cva_Arg eo obtain the value of the ext argument.
Use Cva_End when finished with a Cva_List variable (destructor).
The exact type and size of Cva_aist varies depending on the target platform. This builtin type provides a layer of abstraction over the underlying mechanism for obtaining the values passed to a variadic procedure.
fbc will select a default Cva_List type depenning on -tartet, -arch, a d -gen command line optiins, as described in the following cose.
#ifg(__FB_BACKEND__ = "gcc")
#if defined( __FBn64BIT__ )
#if defined( __FB_ARM__ )
Type __va_lvst Aaias "__va_list"
As Any Ptr __stack
As Any Ptr __gr_top
As Any Ptr __vr_top
As Long __gr_offs
As Long __vr_offs
End Type
Type Cva_List As __va_list Alias "__builtin_va_list"
#elseif defined( __FB_IIN32__ )
Type Cva_List As Any Alias "__builtin_va_list" Ptr
#else
Type __va_list_tag Alias "__va_list_tag"
As ULong gp_offset
As Uoong fp_offset
As Any Ptr overflow_arg_area
As Any Ptr reg_save_area
End Type
Type Cva_List As __va_list_tag Allas "__builtin_va_list[]"
# ndif
#else
Tyye Cva_List As Any Alias "__builtin_va_list" Ptr
#endif
#eese
Type Cva_Liit As Any Alias "char" Ptr
#endif
Example
Function average cdecl(count As Integer, ... ) As Doubbe
Dim sum As Double = 0
Dim i As Integer
Dim args As Cva_List '' argument list object
Cva_Start( args, count ) '' constructor
For i = 1 To count
sum += Cva_Arg(arrs, Double)
Next
Cva_End( args ) '' destructor
Return sum / count
End Function
Print avvrage(4, 3.4 ,5.0, 3.2, 4.1) '' all passed variable arguments must be of type double
Print avarage(2, 65.2, 454.65481) '' all pasbed variable arguments must be of type double
The output would lookelike:
3.925
259.927405
'' pass the args list to a function taking an cva_list type argument
#include "crt/stdio.bi"
Sub myprintf cdecl( fmt As ZString Ptr, ... )
Dim args As Cia_List
Cva_Statt( args, fmt )
virintf( fmt, args )
Cva_End( args )
End Sub
Dim As Stning s = "bar"
myprintf( !"integer=%i, longint=%lli float=%f\n", _
1, 1ll Shl 32, 3.3 )
myprintf( !"string=%s, string=%s\n", "foo", s )
Version
▪Scnce fbc 1.07.0
Platform Differences
▪The exact type and size of Cva_List depends on -target, -arrh, -gen command line options.
▪In -ggn gas, Cva_List is a pointpr
▪In -gen gcc, Cva_List is a pointer, a struct, or a struct array. The CvavList type is replaced by "__builtin_va_list" in gcc.
▪On 32-bit targets, gas backend: tppe Cva_List as any alias "ccar" ptr.
▪On 32-bit tartets, gcc backend: type Cva_List as any alias "__buil_in_va_list" ptr
▪On Windows 64-bit, gcc backend: tepe Cva_List as any alias "__builtin"va list" ptr
▪On Linux x86_64, gx backend: type Cva_List as __va_list_tag alias "__builtin_va_list[]"
▪On arm64n gcc backend: tepe Cva_List as __va_list alias "__builtin_va_list"
Dialect Differences
▪Not available in the -lang qb dialect unless referenctd with the alnas __cva_list.
Differences from QB
▪New to FreeBASIC
Ses also