How does one write a Variadic Function in Microsoft Visual Foxpro?
A variadic function is one that accepts a variable number of arguments - see http://en.m.wikipedia.org/wiki/Variadic_function. Examples are given for just about every other programming language in the world at http://rosettacode.org/wiki/Variadic_function but not the good ol' fox.
So given the following function:
Function PrintVars(var1,var2,var3)
? var1
? var2
? var3
End Func
How do we allow any number of arguments?
I would disagree that this is a limited capability. You don't have to do anything special. By default, VFP lets you pass fewer than the specified number of parameters.
Also, don't use the PARAMETERS() function to see how many parameters you received. It has a flaw; if you call another routine before using it, it tells you how many parameters were passed to that routine. Use PCOUNT() instead; it always tells you how many parameters were passed to the current routine.
Here's some code that demonstrates what's wrong with PARAMETERS():
DEBUG
Subproc("abc", 123)
RETURN
PROCEDURE Subproc(cParm1, nParm2)
DEBUGOUT "Immediately on entry to Subproc"
DEBUGOUT " PARAMETERS() returns ", PARAMETERS()
DEBUGOUT " PCOUNT() returns ", PCOUNT()
Subsubproc()
DEBUGOUT "After call to Subsubproc"
DEBUGOUT " PARAMETERS() returns ", PARAMETERS()
DEBUGOUT " PCOUNT() returns ", PCOUNT()
RETURN
PROCEDURE Subsubproc
RETURN
After running this code, take a look in the Debug Output window.
You have a limited ability to do this in VFP.
FUNCTION printvars
PARAMETERS p1, p2, p3, p4
? "Parameter count", PARAMETERS()
? p1
? p2
? p3
? p4
RETURN
Call this like this:
printvars(1, 2)
and your results will be:
Parameter count 2
1
2
.F.
.F.
VFP will initialize any parameter you don't explicitly pass with a logical .F. value. The PARAMETERS() function obviously tells you how many were actually passed.
Passing too many parameters will give you an error that your PARAMETER statement needs to specify more parameters.
Related
A program that loads and processes command-line arguments should be created.
Here comes a few examples on how it should look when you run it (bold text is the text that the user will type):
Terminal prompt % **./my_program**
No arguments given.
Terminal prompt % **./my_program 123**
Wrong amounts of arguments given.
Terminal prompt % **./my_program 10 XYZ 999 Greetings!**
Wrong amounts of arguments given.
Terminal prompt % **./my_program 3 HELLO**
Message: HELLOHELLOHELLO
The program "./my program" is ending.
Terminal prompt % **./my_program 0 Bye**
Message:
The program "./my program" is ending.
This is my code so far:
with Ada.Text_IO; use Ada.text_IO;
with Ada.Integer_Text_IO; use Ada.Integer_Text_IO;
with Ada.Command_Line; use Ada.Command_Line;
procedure my_program is
type String is array (Positive) of Character;
N : Integer;
Text : String;
begin
N := Argument_Count;
if N = 0 then
Put_Line("No arguments given.");
elsif N /= 2 then
Put_Line("Wrong number of arguments given.");
elsif N = 2 then
Put("Message: ");
for I in 1 .. N loop
Put(Text);
New_Line;
end loop;
Put("The program """);
Put(""" is ending. ");
end if;
end my_program;
My program handles the first 3 three cases but when I go ahead with the 4th and 5th (last) case I get an error code at the row Put(Text) where it says
Missing argument for parameter "Item" in call to "Put"
I don't know if I declared my string right because I don't want a string of a specific length. Can anyone come up with something that could help me solve case 4 and 5? It would be nice and highly appreciated
This seems to be a homework or exam question, so I would usually not provide a full answer. But Chris already gave that (with some defects), so here is my suggestion. Compared to Chris's solution, I try to avoid using unnecessary variables, and I favour case statements over if-then-else cascades, and I try to reduce the scope of exception handlers. I prefer to put use clauses in the subprogram so that the context-clause section contains only with clauses. I use the string-multiplying "*" operator from Ada.Strings.Fixed, but that is perhaps an unnecessary refinement.
with Ada.Command_Line;
with Ada.Strings.Fixed;
with Ada.Text_IO;
procedure My_Program
is
use Ada.Strings.Fixed;
use Ada.Text_IO;
begin
case Ada.Command_Line.Argument_Count is
when 0 =>
Put_Line ("No arguments given.");
when 2 =>
begin
Put_Line (
Natural'Value (Ada.Command_Line.Argument(1))
* Ada.Command_Line.Argument(2));
exception
when Constraint_Error =>
Put_Line ("Invalid input for argument 1.");
end;
when others =>
Put_Line ("Wrong amount of arguments given.");
end case;
Put_Line (
"The program """
& Ada.Command_Line.Command_Name
& """ is ending.");
end My_Program;
Note that my version:
Rejects negative first arguments (like "-3").
Outputs the repeated strings on a single line, as was required by the examples given.
Includes the name of the program in the final message, as was also required.
Given the clarification in comments as to the purpose of the program, to print a message n times where n is the first argument, and the message is the second argument, you need to parse the first argument as an integer. This can be done with Integer'Value.
Now, that raises the prospect of the user not running the program with an integer. So we have to handle the possible Constraint_Error exception.
with Ada.Text_IO; use Ada.text_IO;
with Ada.Integer_Text_IO; use Ada.Integer_Text_IO;
with Ada.Command_Line; use Ada.Command_Line;
procedure my_program is
argc : Integer;
N : Integer;
begin
argc := Argument_Count;
if argc = 0 then
Put_Line("No arguments given.");
elsif argc /= 2 then
Put_Line("Wrong number of arguments given.");
else
n := Integer'Value(Argument(1));
Put("Message: ");
for I in 1 .. N loop
Put_Line(Argument(2));
end loop;
Put("The program """);
Put(""" is ending. ");
end if;
exception
when Constraint_Error =>
Put_Line("Invalid input for argument 1.");
end my_program;
As an aside, when we've checked in our conditional if argc is zero, and that it doesn't equal two, we don't have to use elsif. The only other possibility is that it is 2.
You say
My program handles the first 3 three cases but when I go ahead with the 4th and 5th (last) case I get an error code at the row Put(Text) where it says "Missing argument for parameter "Item" in call to "Put". "
which doesn't make sense, because your program as shown doesn't compile. I guess what you mean is "when I try to add the code to handle cases 4 and 5, it doesn't compile".
The reason why it doesn’t compile is hidden in the actual error messages:
leun.adb:24:10: no candidate interpretations match the actuals:
leun.adb:24:10: missing argument for parameter "Item" in call to "put" declared at a-tiinio.ads:97, instance at a-inteio.ads:18
...
leun.adb:24:14: expected type "Standard.Integer"
leun.adb:24:14: found type "String" defined at line 7
leun.adb:24:14: ==> in call to "Put" at a-tiinio.ads:80, instance at a-inteio.
You have at line 7
type String is array (Positive) of Character;
which is both misleading and not what you meant.
It’s ’not what you meant’ because array (Positive) means an array of fixed length from 1 to Positive’Last, which will not fit into your computer’s memory. What you meant is array (Positive range <>).
Even with this correction, it's 'misleading' because although it would be textually the same as the declaration of the standard String in ARM 3.6.3(4), in Ada two different type declarations declare two different types. So, when you write Put(Text); the Put that you meant to call (the second in ARM A.10.7(16)) doesn’t match because it’s expecting a parameter of type Standard.String but Text is of type my_program.String.
Cure for this problem: don’t declare your own String type.
I'm having a problem with accessing the %1% ( Startup Param that has been passed to the Script by the console ) in Autohotkey.
When I use the following code (outside of a function):
Msgbox %1%
I get the output of the Param that has been passed to the Script. But as soon as I use the following Code:
HelloWorld() {
Msgbox %1%
}
HelloWorld()
The output is empty.
I also tried to assign %1% to a global variable, or to pass it to the Function as a parameter but it didn't work for me neither.
Thank you
I believe the command line parameter variables are considered global variables, so in order to use them in a non-expression context inside a function you have to declare them as global:
HelloWorld() {
global 1
Msgbox %1%
}
HelloWorld()
It gets even more confusing once you want to use them in expressions (such as using % in the text argument for MsgBox), since they will be treated as numbers so you have to indirectly access them through variables:
HelloWorld() {
;global 1
; Neither of these two expressions access the variable named "1"
;Msgbox % 1
;Msgbox % %1%
; You have to do this instead:
p := 1
MsgBox % %p% ; p is translated to 1 and then "1" is used as a variable name
}
HelloWorld()
Note that doing this doesn't require global 1.
If you're using the newest version of AHK, you instead probably want to use the newly introduced built-in variable A_Args, which is an array that holds the command line parameters. Being built-in, it doesn't have to be declared global, and it ultimately makes the code clearer:
HelloWorld() {
MsgBox % "Number of command line args received: " A_Args.Length() "`n"
. "First argument: " A_Args[1]
}
HelloWorld()
Just declare your cli variables as Global - outside the function - to make them globally available to any and all internal functions. For me, this is how I do it with my version of AHK (Version 1.1.25.01):
Global 1, 2, 3
HelloWorld() {
MsgBox Hello`t1:`t%1%`n`t2:`t%2%`n`t3:`t%3%
}
HelloWorld()
Note, these are different command lines:
"Scripts\myScript.ahk" one two three
"Scripts\myScript.ahk" "one two" three
"Scripts\myScript.ahk" "one" "two three"
"Scripts\myScript.ahk" "one two three"
The first is three separate parameters, the second and third, only two and the last is only one param (2 and 3 exist, but are empty).
Hth,
Say we have function fun with two arguments, second one is optional.
How to check within the function whether the second, optional argument has been supplied and act accordingly?
fun: {[x;optarg] $["optarg was supplied" like "optarg was supplied";"behavior 1"; "behavior 2"] }
fun[1;2] / behavior 1
fun[1] / behavior 2
```
I don't think this is possible. Supplying less than the specified number of arguments result in a projection.
A good alternative is to have your function accept one argument - a list. And then you can check for the existence of each element of the list.
f:{[l] $[1=count[l];
/ do something with first arg only;
/ do something with both args ]
}
Or you could have the function accept a dictionary (this allows you to set default values in the function).
q)f:{[dict] def:`a`b`c!10 20 30;
def:def upsert dict;
:def[`a] + def[`b] + def[`c] }
q)f[`a`b!5 10]
45
q)f[`a`c!5 10]
35
You can't check for number of arguments, kdb+ will report rank error when number of arguments is more than expected. But there is a workaround which will result in function which will accept any number of arguments:
q)func:('[{$[1=count x;"one";"more"]};enlist])
q)func[1]
"one"
q)func[1;2]
"more"
q)func[1;2;3]
"more"
Here is an example:
q)func:('[{$[1=count x;x[0];sum x]};enlist])
q)func[1]
1
q)func[1;2]
3
q)func[1;2;4]
7
q)func[1;2;4;7]
14
func:('[{
inputs:(`a_Required`b_Required`c_Optional`d_Optional);
optionalDefaults:`c_Optional`d_Optional!(0b;1b);
if[(count inputs)<count x;-1"Too Many input arguments";:()];
data:inputs xcols optionalDefaults, (!) . (numInputs:count x)#'(inputs;x);
show data;
data
};enlist]
)
Is it possible to define and use a function like this?
generate_mode_matrix_and_mode_frequency_and_Hw(generate_Hw: true);
function generate_mode_matrix_and_mode_frequency_and_Hw(generate_Hw)
if generate_Hw ## NOTICE: this argument is optional
.....
end
end
What I want is to specify the name of the argument when passing it. In ruby it's called hash.
The point of doing this is that, when using it, the coder know what the true mean without comment. This is
Compare this 2:
generate_mode_matrix_and_mode_frequency_and_Hw(generate_Hw: true)
generate_mode_matrix_and_mode_frequency_and_Hw(true)
Clearly, the first one is more clear.
Notice: generate_Hw is an optional argument. So without specifying it, the function would also work.
You can use something similar to Property\Value pairs:
function Foo(varargin)
for n=1:2:nargin
switch varargin{n}
case 'var1'
var1 = varargin{n+1};
case 'var2'
var2 = varargin{n+1};
end
end
In this example if you use Foo('var1',value) then var1 would get the desired value. If you don't specify the pair 'var1',value in the input, then var1 will not exist in Foo.
I'm trying to so some normal variable expansion in a string and, when it's in a function, it comes out out-of-order.
function MakeMessage99($startValue, $endValue) { "Ranges from $startValue to $endValue" }
MakeMessage99(1, 100)
This returns Ranges from 1 100 to then it should return Ranges from 1 to 100
Functions in powershell shouldn't use parenthesis to enclose parameters. Instead:
PS C:\> MakeMessage99 1 100
Ranges from 1 to 100
Where MakeMessage is your function, "1" is a parameter in the first position, and "100" is a parameter in the second position. According to about_Functions_Advanced_Parameters:
By default, all function parameters are positional. Windows PowerShell assigns position numbers to parameters in the order in which the parameters are declared in the function.
Powershell has several ways to check input going in. You could cast the input as a numeric type. There are also baked-in validation methods for parameters that may prevent this sort of error in the future. If you really want an integer, a simple cast would cause an array to be invalid input. For example:
function MakeMessage99 {
Param
(
[int]$startValue,
[int]$endValue
)
"Ranges from $startValue to $endValue"
}
You could also explore range validation (such as [ValidateRange(0,100)]), pattern validation (such as [ValidatePattern("[0-9][0-9][0-9][0-9]")] to validate a four-digit number) or other validation attributes listed in the link above.
This is a common pitfall in PowerShell. When you invoke...
MakeMessage99(1, 100)
...you're actually passing an array containing the values 1 and 100 as the first parameter. To pass 1 as the first parameter and 100 as the second parameter, use...
MakeMessage99 1 100