Title: How to create functions that can accept variable number of parameters such as Format()?
Question: How to create functions that can accept variable number of parameters such as Format()?
Answer:
Sometimes it's necessary to pass undefined number of [different type] variables
to a function -- look at Format() function in Delphi and *printf() functions in
C/C++ for example. Once you analyze the following code, you'll be on your way to creating mysterious variable parameter functions...
{
FunctionWithVarArgs()
skeleton for a function that can accept vairable number of multi-type variables here are some examples on how to call this function:
FunctionWithVarArgs([ 1, True, 3, '5', '0' ] );
FunctionWithVarArgs([ 'one', 5 ] );
FunctionWithVarArgs([]);
}
procedure FunctionWithVarArgs(const ArgsList: array of const);
var
ArgsListTyped: array[0..$FFF0 div SizeOf(TVarRec)] of TVarRec absolute ArgsList;
n: integer;
begin
for n := Low(ArgsList) to
High(ArgsList) do
begin
with ArgsListTyped[n] do
begin
case VType of
vtInteger: begin
{handle VInteger here}
end;
vtBoolean: begin
{handle VBoolean here}
end;
vtChar: begin
{handle VChar here}
end;
vtExtended: begin
{handle VExtended here}
end;
vtString: begin
{handle VString here}
end;
vtPointer: begin
{handle VPointer here}
end;
vtPChar: begin
{handle VPChar here}
end;
vtObject: begin
{handle VObject here}
end;
vtClass: begin
{handle VClass here}
end;
vtWideChar: begin
{handle VWideChar here}
end;
vtPWideChar: begin
{handle VPWideChar here}
end;
vtAnsiString: begin
{handle VAnsiString here}
end;
vtCurrency: begin
{handle VCurrency here}
end;
vtVariant: begin
{handle VVariant here}
end;
else
begin
{handle unknown type here}
end;
end;
end;
end;
end;
{
example function created using the above skeleton
AddNumbers() will return the sum of all the integers passed to it
AddNumbers( [1, 2, 3] ) will return 6
}
function AddNumbers(const ArgsList: array of const): integer;
var
ArgsListTyped: array[0..$FFF0 div SizeOf(TVarRec)] of TVarRec absolute ArgsList;
n: integer;
begin
Result := 0;
for n := Low(ArgsList) to
High(ArgsList) do
begin
with ArgsListTyped[n] do
begin
case VType of
vtInteger: Result := Result + VInteger;
end;
end;
end;
end;