What does var mean in C

Question

In C   how does keyword var work

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It means the data type is derived  implied  from the context   From http   msdn microsoft com en-us library bb383973 aspx     Beginning in Visual C  3 0  variables   that are declared at method scope can   have an implicit type var  An   implicitly typed local variable is   strongly typed just as if you had   declared the type yourself  but the   compiler determines the type  The   following two declarations of i are   functionally equivalent    var i   10     implicitly typed int i   10    explicitly typed   var is useful for eliminating keyboard typing and visual noise  e g    MyReallyReallyLongClassName x   new MyReallyReallyLongClassName      becomes  var x   new MyReallyReallyLongClassName      but can be overused to the point where readability is sacrificed

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Did you ever hated to write such variable initializers   XmlSerializer xmlSerializer   new XmlSerialzer typeof int     So  starting with C  3 0  you can replace it with  var xmlSerializer   new XmlSerialzer typeof int     One notice  Type is resolved during compilation  so no problems with performance  But Compiler should be able to detect type during build step  so code like var xmlSerializer  won t compile at all

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It means that the type of the local being declared will be inferred by the compiler based upon its first assignment     This statement  var foo    quot bar quot      Is equivalent to this statement  string foo    quot bar quot    Notably  var does not define a variable to be of a dynamic type   So this is NOT legal  var foo    quot bar quot   foo   1     Compiler error  the foo variable holds strings  not ints  var has only two uses   It requires less typing to declare variables  especially when declaring a variable as a nested generic type  It must be used when storing a reference to an object of an anonymous type  because the type name cannot be known in advance  var foo   new   Bar    quot bar quot      You cannot use var as the type of anything but locals   So you cannot use the keyword var to declare field property parameter return types

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var  means the compiler will determine the explicit type of the variable  based on usage  For example   var myVar   new Connection      would give you a variable of type Connection

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var is a  contextual keyword  in C  meaning you can only use it as a local variable implicitly in the context of the same class that you are using the variable  If you try to use it in a class that you call from  Main  or some other exterior class  or an interface for example you will get the error CS0825  lt  https   docs microsoft com en-us dotnet csharp misc cs0825    See the remarks about when you can and can t use it in the documentation here   lt  https   docs microsoft com en-us dotnet csharp programming-guide classes-and-structs implicitly-typed-local-variables remarks    Basically  you should only use this when you are declaring a variable with an implicit value such as  var myValue    This is the value   This saves a little time in comparison to saying  string  for example but IMHO not much time is saved and places a constraint on the scalability of your project

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As the name suggested  var is variable without any data type  If you don t know which type of data will be returned by any method  such cases are good for using var  var is Implicit type which means system will define the data type itself  The compiler will infer its type based on the value to the right of the     operator  int string etc  are the explicit types as it is defined by you explicitly  Var can only be defined in a method as a local variable Multiple vars cannot be declared and initialized in a single statement  For example  var i 1  j 2  is invalid    int i   100    explicitly typed  var j   100     implicitly typed

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It declares a type based on what is assigned to it in the initialisation   A simple example is that the code   var i   53    Will examine the type of 53  and essentially rewrite this as   int i   53    Note that while we can have   long i   53    This won t happen with var  Though it can with   var i   53l     i is now a long   Similarly   var i   null     not allowed as type can t be inferred  var j    string  null     allowed as the expression  string  null has both type and value    This can be a minor convenience with complicated types  It is more important with anonymous types   var i   from x in SomeSource where x Name Length  gt  3 select new  x ID  x Name   foreach var j in i    Console WriteLine j ID ToString           j Name     Here there is no other way of defining i and j than using var as there is no name for the types that they hold

[c#] What does "var" mean in C#?

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