As the title says I need to know if there is a corresponding syntax as java's ... in method parameters, like
void printReport(String header, int... numbers) { //numbers represents varargs
System.out.println(header);
for (int num : numbers) {
System.out.println(num);
}
}
(code courtesy of wikipedia)
Yes you can write something like this:
void PrintReport(string header, params int[] numbers)
{
Console.WriteLine(header);
foreach (int number in numbers)
Console.WriteLine(number);
}
Try using the params keyword, placed before the statement, eg
myFunction(params int[] numbers);
Yes, there is. As Adriano said you can use C# 'params' keyword.
An example is the in link below:
params (C# Reference)
http://msdn.microsoft.com/en-us/library/w5zay9db.aspx
"The params keyword lets you specify a method parameter that takes a variable number of arguments.
You can send a comma-separated list of arguments of the type specified in the parameter declaration, or an array of arguments of the specified type. You also can send no arguments.
No additional parameters are permitted after the params keyword in a method declaration, and only one params keyword is permitted in a method declaration."
You can declare a method to har a variable number of parameters by using the params keyword. Just like when using ... in Java, this will give you an array and let you call the metods with a variable number of parameters:
http://msdn.microsoft.com/en-us/library/w5zay9db(v=vs.71).aspx
This should be
void printReport(String header, params int[] numbers)
I believe you mean params
public void printReport(string header, params int[] list)
{
Console.WriteLine(header);
for (int i = 0 ; i < list.Length; i++)
{
Console.WriteLine(list[i]);
}
Console.WriteLine();
}
You can use params, although this must always come last in the list:
public void PrintReport(string header, params int[] numbers)
{
It is however possible to combine params optional parameters (such as [CallerMemberName]) by using named arguments, which works even if the parameters are of the same type.
Declare the method like this:
public static void PrintReport(
[CallerMemberName] string callerName = "",
[CallerFilePath] string sourceFilePath = "",
params string[] inputStrings)
{
and call it like this:
PrintReport(inputStrings: new[] { "string 1", "string 2" } );
Related
Can I implicitly create an array from one single element in C#?
For instance, I have this method
public void MyMethod(string[] arrayString)
At some point in my code I have
string str = "myStr";
MyMethod(str)
Of course the second linhe is an error, because I am passing a string while MyMethod expects a string[].
Is there any clean way to call MyMethod without using
MyMethod(new string[] {str})
If you use a params array, this will be fine:
public void MyMethod(params string[] arrayString)
string str = "myStr";
MyMethod(str)
The only way I know would be to overload the method, so that you also have
MyMethod(string)
{
return MyMethod(new string[] {str});
}
You might be able to do it with a params array, but I'm not entirely sure how that would work if you tried to pass in a string array, rather than multiple strings.
I would just add a second overload of MyMethod
public void MyMethod(string str)
{
MyMethod(new[]{str});
}
For the sake of completeness, here's another couple of options, though surely not recommended -- I'd use params as in the accepted answer.
MyMethod(Enumerable.Repeat(str, 1).ToArray());
I've also seen this on occasion, though it's hard to justify unless you're unaware of array initializers:
T[] MakeArray<T>(params T[] elements)
{
return elements;
}
used thus:
string[] grades = MakeArray("A", "B", "C", "D", "F", "Incomplete");
or, in this case:
MyMethod(MakeArray(str));
How about an extension method?
public static T[] WrapInArray<T>(this T t)
{
return new T[]{ t };
}
For example, printf in c can take any number of parameters like printf("%d %d %s %s...",a,b,c,d,...) and is documented as below
printf( const char *format [, argument]... );
How can I define such functions in C#?
Using the params keyword:
void WriteAll(params object[] args) {
for(int i = 0; i < args.Length; i++)
Console.WriteLine(args[i]);
}
args will be an array with all the arguments you pass. Note that it must be the last formal argument.
use params object[] arg as the last argument.
http://msdn.microsoft.com/en-us/library/w5zay9db%28v=vs.71%29.aspx
see for more detail
private void Print(params object[] values)
{
foreach (var item in values)
{
Console.WriteLine(item);
}
}
this code will print to the console every item you'll send at the object array using the "params" keyword. you can call this method with as many parameters you like (or none).
link:
http://msdn.microsoft.com/en-us/library/w5zay9db(v=vs.110).aspx
in c# the you'll use the params key word.
public static void UseParams2(params object[] list)
{
for (int i = 0; i < list.Length; i++)
{
Console.Write(list[i] + " ");
}
Console.WriteLine();
}
Just pass an object with your parameters
private void MyVoid(MyParameterObject params)
{
}
There are several approaches in this case:
You can define a type that holds all fields you need to pass and return between methods. Better then simple object array, cause it's typesafe.
You can define dictionary where place parameter names and values. Better then simple object array, cause it's typesafe.
(This depends on quantity of the parameters, and on use logic of the code) You can define overrloads of the same function.
func A (AA aa)
func A(AA aa, BB bb =null)
func A(AA aa, BB bb = null, CC cc = null)
and so on...
Can I forward a params parameter to another method?
e.g.,
void MyStringMethod(string format, params object[] list)
{
String.Format(format, list);
}
Works for me.
void Main()
{
Method1("{0},{1},{2},{3}","Can","I","do","this").Dump();
}
String Method1(string format, params object[] list)
{
return String.Format(format,list);
}
returns
Can,I,do,this
yes ... but!
I know this is technically not a different answer, however I've been burned so many times with really hard to debug errors (caused by using params in what looked like really simple scenarios) that I feel compelled to post this comment.
Please be very careful when you use params. Ideally don't use them, unless you feel you absolutely have to, and then make sure you don't use the same data type in front of the params! This can make quickly reading the code (scanning) it and knowing what it will do very difficult, or worse, give you an unexpected and hard to find bug.
For example, in the code below, it's not easy to see what will be printed to the Console. Is the (1,2,3) being passed to WhoKnocked actually being identified as int 1 followed by int[] [2,3] or perhaps int[] [1,2,3]?
void Main()
{
Console.WriteLine(WhoKnocked(1,2,3));
}
public string WhoKnocked(int x, params int[] knocks)
{
return "It's mee!";
}
public string WhoKnocked(params int[] knocks)
{
return "No, it's not, its you!";
}
lastly, here's another example that might give you some surprising results.
void Main()
{
Greet(1,"foo", "bar");
Greet(1, 2, "bar");
Greet(1,"foo", new object());
Greet(1,2,3);
Greet(1,2,3,4);
}
public void Greet(int i, params object[] foo)
{
Console.WriteLine("Number then param array of objects!");
}
public void Greet(int i, int x, params object[] foo)
{
Console.WriteLine("Number, ...nuther number, and finally object[]!");
}
public void Greet(int i, string x, params object[] foo)
{
Console.WriteLine("number, then string, then object[]!");
}
produces the following output
Number, then String, then Object[]!
Number, ...nuther Number, and finally Object[]!
Number, then String, then Object[]!
Number, ...nuther Number, and finally Object[]!
Number, ...nuther Number, and finally Object[]!
The params keyword is just a form of syntactic sugar designed to allow you to make method calls as if they had a dynamic parameter count. All it is really is just a compiler transformation of multiple arguments to an array instantiation. That's all it is, an array.
An array is just another object that could be passed to other methods and whatnot so yes, you can forward that array of you wish.
I believe you can, it is just an array of objects. If you then call another function that expects a param list then you can get unexpected results (depending on what you expect of course:-). Notice in the third case you only get 2 params.
void Test()
{
DoIt(1, 2, 3, 4);
}
private void DoIt(params object[] p)
{
Console.WriteLine(p.Length);
DoIt2(p);
DoIt2(p, 5);
}
private void DoIt2(params object[] p)
{
Console.WriteLine(p.Length);
}
Does C# support a variable number of arguments?
If yes, How does C# support variable no of arguments?
What are the examples?
How are variable arguments useful?
EDIT 1: What are the restrictions on it?
EDIT 2: The Question is not about Optional param But Variable Param
Yes. The classic example wourld be the params object[] args:
//Allows to pass in any number and types of parameters
public static void Program(params object[] args)
A typical usecase would be passing parameters in a command line environment to a program, where you pass them in as strings. The program has then to validate and assign them correctly.
Restrictions:
Only one params keyword is permitted per method
It has to be the last parameter.
EDIT: After I read your edits, I made mine. The part below also covers methods to achieve variable numbers of arguments, but I think you really were looking for the params way.
Also one of the more classic ones, is called method overloading. You've probably used them already a lot:
//both methods have the same name and depending on wether you pass in a parameter
//or not, the first or the second is used.
public static void SayHello() {
Console.WriteLine("Hello");
}
public static void SayHello(string message) {
Console.WriteLine(message);
}
Last but not least the most exiting one: Optional Arguments
//this time we specify a default value for the parameter message
//you now can call both, the method with parameter and the method without.
public static void SayHello(string message = "Hello") {
Console.WriteLine(message);
}
http://msdn.microsoft.com/en-us/library/dd264739.aspx
C# supports variable length parameter arrays using the params keyword.
Here's an example.
public static void UseParams(params int[] list)
{
for (int i = 0; i < list.Length; i++)
{
Console.Write(list[i] + " ");
}
Console.WriteLine();
}
There's more info here.
Yes, params:
public void SomeMethod(params object[] args)
params has to be the last argument and can be of any type. Not sure if it has to be an array or just an IEnumerable.
I assume you mean a variable number of method parameters. If so:
void DoSomething(params double[] parms)
(Or mixed with fixed parameters)
void DoSomething(string param1, int param2, params double[] otherParams)
Restrictions:
They must all be the same type (or of a child type) as is true for arrays as well
There can only be one for each method
They must come last in the parameter list
That's all I can think of at the moment though there could be others. Check the documentation for more information.
Is there an equivalent to func_get_arg (php) in C#?
func_get_arg ( int $arg_num ):
Gets the specified argument from a user-defined function's argument list.
This function may be used in conjunction with func_get_args() and func_num_args() to allow user-defined functions to accept variable-length argument lists.
It basically means the index can be used to get the argument value...
Thanks
C# is statically typed, so function signatures matter. You can't just call a method with any number of arguments, which really means there is no need for func_get_arg.
That said, you can get pretty close if you have a method such as this one:
void MyMethod(params object[] args)
{
var indexOfArgument = 42; // or whatever
var valueOfArgument = args[indexOfArgument]; // should also check array bounds
}
Of course if all your arguments are typed as System.Object there's not much you can do with them, but from a syntactic viewpoint it's close (plus, you could also have a method that accepts params T[] args for any type T).
in C# there's a method "__arglist()"
or you can easily make a function accept variable number of parameters like this
int Average(params int[] ints)
{
int total = 0;
foreach(int i in ints) // loop to the number of parameters
total += i;
return (ints.Length > 0 ? total / ints.Length : 0);
}
As I understand it, the purpose of func_get_arg in PHP is to have a variable number of arguments to a function. Here's the equivilent to that in C#:
public void Foo(string realArg, int anotherRealArg, params int[] variableArgs)
{
Console.WriteLine("My real string argument was " + realArg);
Console.WriteLine("My real integer argument was " + anotherRealArg);
Console.WriteLine("And I was given " + variableArgs.Length + " extra arguments");
}
// Usage
Foo("Bar", 1, 2, 3, 4, 5);
Within the method, variableArgs is a regular array. Before accessing it, you'll want to check its Length to be sure you don't get an IndexOutOfRangeException.