Value assignment in C#

Question

Without initialization how is it possible to assign values to arrays?

string[] s={"all","in","all"};

I mean why did not the compile show error?.Normally we need to 
initialize ,before assign values.

Just like you showed... Or I don't get the question-part here. — Henk Holterman
– Henk Holterman, Commented Oct 21, 2009 at 18:33
Have we discovered the stackoverflow equivalent of 'how is babby formed?' — Chris
– Chris, Commented Oct 21, 2009 at 18:45
@Seth Smart answer.But Just i finised schooling.I am learning C#.If you know answer of your question explain me Mr Mega Genious. — user193276
– user193276, Commented Oct 21, 2009 at 18:49
You should read section 7.5.10 of the C# specification; it answers all your questions that you've posted here -- how array, object and collection initializers work in C# 3.0. — Eric Lippert
– Eric Lippert, Commented Oct 21, 2009 at 20:58

SolutionYogi · Accepted Answer · 2009-11-27 16:34:45Z

6

It's just syntactic sugar.

This:

string[] s = {"all","in","all"};

is compiled to the same code as:

string[] tmp = new string[3];
tmp[0] = "all";
tmp[1] = "in";
tmp[2] = "all";
string[] s = tmp;

Note that the array reference is not assigned to s until all the elements have been assigned. That isn't important in this particular case where we're declaring a new variable, but it would make a different in this situation:

string[] s = { "first", "second" };
s = new string[] { s[1], s[0] };

The same is true for object and collection initializers - the variable is only assigned at the end.

edited Nov 27, 2009 at 16:34

SolutionYogi

32.4k12 gold badges73 silver badges79 bronze badges

answered Oct 21, 2009 at 18:50

Jon Skeet

1.5m893 gold badges9.3k silver badges9.3k bronze badges

Sign up to request clarification or add additional context in comments.

11 Comments

user193276 Over a year ago

Is this relaxation for Array only?

Neil N Over a year ago

ooh I found a bug in John Skeet's code! s is not defined, line 2. I think you meant tmp[0] = "all";

Jon Skeet Over a year ago

@generix: What exactly do you mean by "relaxation"? It's just a form of syntax.

el2iot2 Over a year ago

@Neil heheh...I confirm...it did just happen :D

Eric Lippert Over a year ago

Interestingly enough, int[] x = {1, 2, 3} does NOT generate the same code as int[] tmp = new int[3]; tmp[0] = 1; tmp[1] = 2; tmp[2] = 3; int[] x = tmp. :-)

|

madan · Accepted Answer · 2009-10-21 18:37:38Z

3

It is possible to declare an array variable without initialization.

Check this out http://msdn.microsoft.com/en-us/library/0a7fscd0%28VS.71%29.aspx

answered Oct 21, 2009 at 18:37

madan

971 silver badge9 bronze badges

2 Comments

Bob Over a year ago

declaring an array without initialization would just be string[] s the example above provides values which the string is initialized with.

Bob Over a year ago

the example above provides values which the string array is initialized with

Pavel Minaev · Accepted Answer · 2009-10-21 18:41:26Z

3

You aren't "assigning a value to array". You are initializing a variable of type "reference to array". The value with which you initialize it is a reference to an array which was created by the use of short array initializer syntax {...}. While it is only permissible in initializer of variables of array type, it is exactly equivalent to new T[] { ... }, where T is deduced from type of variable.

answered Oct 21, 2009 at 18:41

Pavel Minaev

102k27 gold badges222 silver badges293 bronze badges

Comments

Jon Norton · Accepted Answer · 2009-10-21 21:58:33Z

2

I think you want to know why

 string[] s={"all","in","all"};

works when you would expect to be required to initialize the array first like this :

string[] s = new string[];

or

string[] s = new string[] {"all","in","all"};

The answer is just compiler magic. The compiler knows based on the initialization how big to make the array so it just does it behind the scenes for you. Much like the var keyword, the point is to limit the amount of redundant information you're required to type.

edited Oct 21, 2009 at 21:58

answered Oct 21, 2009 at 18:39

Jon Norton

3,01922 silver badges21 bronze badges

1 Comment

user193276 Over a year ago

Is this relaxation for arrays only? Pesron a={ Name="somename"} ??

Bob · Accepted Answer · 2009-10-21 18:35:05Z

1

The {"all","in","all"} part is the initialization. the new string[] part can be omitted because the curly braces and string are short hand notation. Take a look at MSDN on Single Dimension Arrays.

answered Oct 21, 2009 at 18:35

Bob

100k30 gold badges127 silver badges131 bronze badges

Comments

el2iot2 · Accepted Answer · 2009-10-21 18:40:00Z

1

string[] s = new string[] { "all","in","all"};

and its shorthand version

string[] s = {"all","in","all"};

are the same thing. See MSDN (Initializing Arrays section) for more detail.

edited Oct 21, 2009 at 18:40

answered Oct 21, 2009 at 18:34

el2iot2

6,6468 gold badges42 silver badges52 bronze badges

Comments

Dan Diplo · Accepted Answer · 2009-10-21 18:41:27Z

1

You don't need the new string[] part in C#3 or higher - this works fine

string[] s = { "all","in","all"};

It's just a case of the compiler being a bit smarter and working out what you mean - the back end IL will be the same.

answered Oct 21, 2009 at 18:41

Dan Diplo

25.4k4 gold badges71 silver badges90 bronze badges

Comments

Chris · Accepted Answer · 2009-10-21 18:47:58Z

0

You can do so simply because it is allowed, doing so in two steps is not necessary so this is the shorthand. Consider it sugar.

answered Oct 21, 2009 at 18:47

Chris

3763 silver badges4 bronze badges

Collectives™ on Stack Overflow

Value assignment in C#

8 Answers 8

11 Comments

2 Comments

Comments

1 Comment

Comments

Comments

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

8 Answers 8

11 Comments

2 Comments

Comments

1 Comment

Comments

Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related