with - string vs string c#




What is the difference between String and string in C#? (20)

Against what seems to be common practice among other programmers, I prefer String over string , just to highlight the fact that String is a reference type, as Jon Skeet mentioned.

https://code.i-harness.com

Example ( note the case ):

string s = "Hello world!";
String s = "Hello world!";

What are the guidelines for the use of each? And what are the differences ?


As the others are saying, they're the same. StyleCop rules, by default, will enforce you to use string as a C# code style best practice, except when referencing System.String static functions, such as String.Format , String.Join , String.Concat , etc...


C# is a language which is used together with the CLR.

string is a type in C#.

System.String is a type in the CLR.

When you use C# together with the CLR string will be mapped to System.String .

Theoretically, you could implement a C#-compiler that generated Java bytecode. A sensible implementation of this compiler would probably map string to java.lang.String in order to interoperate with the Java runtime library.


Coming late to the party: I use the CLR types 100% of the time (well, except if forced to use the C# type, but I don't remember when the last time that was).

I originally started doing this years ago, as per the CLR books by Ritchie. It made sense to me that all CLR languages ultimately have to be able to support the set of CLR types, so using the CLR types yourself provided clearer, and possibly more "reusable" code.

Now that I've been doing it for years, it's a habit and I like the coloration that VS shows for the CLR types.

The only real downer is that auto-complete uses the C# type, so I end up re-typing automatically generated types to specify the CLR type instead.

Also, now, when I see "int" or "string", it just looks really wrong to me, like I'm looking at 1970's C code.


I'd just like to add this to lfousts answer, from Ritchers book:

The C# language specification states, “As a matter of style, use of the keyword is favored over use of the complete system type name.” I disagree with the language specification; I prefer to use the FCL type names and completely avoid the primitive type names. In fact, I wish that compilers didn’t even offer the primitive type names and forced developers to use the FCL type names instead. Here are my reasons:

  • I’ve seen a number of developers confused, not knowing whether to use string or String in their code. Because in C# string (a keyword) maps exactly to System.String (an FCL type), there is no difference and either can be used. Similarly, I’ve heard some developers say that int represents a 32-bit integer when the application is running on a 32-bit OS and that it represents a 64-bit integer when the application is running on a 64-bit OS. This statement is absolutely false: in C#, an int always maps to System.Int32 , and therefore it represents a 32-bit integer regardless of the OS the code is running on. If programmers would use Int32 in their code, then this potential confusion is also eliminated.

  • In C#, long maps to System.Int64 , but in a different programming language, long could map to an Int16 or Int32 . In fact, C++/CLI does treat long as an Int32 . Someone reading source code in one language could easily misinterpret the code’s intention if he or she were used to programming in a different programming language. In fact, most languages won’t even treat long as a keyword and won’t compile code that uses it.

  • The FCL has many methods that have type names as part of their method names. For example, the BinaryReader type offers methods such as ReadBoolean , ReadInt32 , ReadSingle , and so on, and the System.Convert type offers methods such as ToBoolean , ToInt32 , ToSingle , and so on. Although it’s legal to write the following code, the line with float feels very unnatural to me, and it’s not obvious that the line is correct:

    BinaryReader br = new BinaryReader(...);
    float val = br.ReadSingle(); // OK, but feels unnatural
    Single val = br.ReadSingle(); // OK and feels good
  • Many programmers that use C# exclusively tend to forget that other programming languages can be used against the CLR, and because of this, C#-isms creep into the class library code. For example, Microsoft’s FCL is almost exclusively written in C# and developers on the FCL team have now introduced methods into the library such as Array ’s GetLongLength , which returns an Int64 value that is a long in C# but not in other languages (like C++/CLI). Another example is System.Linq.Enumerable ’s LongCount method.

I didn't get his opinion before I read the complete paragraph.


It's a matter of convention, really. string just looks more like C/C++ style. The general convention is to use whatever shortcuts your chosen language has provided (int/Int for Int32 ). This goes for "object" and decimal as well.

Theoretically this could help to port code into some future 64-bit standard in which "int" might mean Int64 , but that's not the point, and I would expect any upgrade wizard to change any int references to Int32 anyway just to be safe.


Just for the sake of completeness, here's a brain dump of related information...

As others have noted, string is an alias for System.String . They compile to the same code, so at execution time there is no difference whatsoever. This is just one of the aliases in C#. The complete list is:

object:  System.Object
string:  System.String
bool:    System.Boolean
byte:    System.Byte
sbyte:   System.SByte
short:   System.Int16
ushort:  System.UInt16
int:     System.Int32
uint:    System.UInt32
long:    System.Int64
ulong:   System.UInt64
float:   System.Single
double:  System.Double
decimal: System.Decimal
char:    System.Char

Apart from string and object , the aliases are all to value types. decimal is a value type, but not a primitive type in the CLR. The only primitive type which doesn't have an alias is System.IntPtr .

In the spec, the value type aliases are known as "simple types". Literals can be used for constant values of every simple type; no other value types have literal forms available. (Compare this with VB, which allows DateTime literals, and has an alias for it too.)

There is one circumstance in which you have to use the aliases: when explicitly specifying an enum's underlying type. For instance:

public enum Foo : UInt32 {} // Invalid
public enum Bar : uint   {} // Valid

That's just a matter of the way the spec defines enum declarations - the part after the colon has to be the integral-type production, which is one token of sbyte , byte , short , ushort , int , uint , long , ulong , char ... as opposed to a type production as used by variable declarations for example. It doesn't indicate any other difference.

Finally, when it comes to which to use: personally I use the aliases everywhere for the implementation, but the CLR type for any APIs. It really doesn't matter too much which you use in terms of implementation - consistency among your team is nice, but no-one else is going to care. On the other hand, it's genuinely important that if you refer to a type in an API, you do so in a language neutral way. A method called ReadInt32 is unambiguous, whereas a method called ReadInt requires interpretation. The caller could be using a language which defines an int alias for Int16 , for example. The .NET framework designers have followed this pattern, good examples being in the BitConverter , BinaryReader and Convert classes.


Lower case string is an alias for System.String . They are the same in C# .

There's a debate over whether you should use the System types ( System.Int32 , System.String , etc.) types or the C# aliases ( int , string , etc). I personally believe you should use the C# aliases , but that's just my personal preference.


String ( System.String ) is a class in the base class library. string (lower case) is a reserved work in C# that is an alias for System.String. Int32 vs int is a similar situation as is Boolean vs. bool . These C# language specific keywords enable you to declare primitives in a style similar to C.


The best answer I have ever heard about using the provided type aliases in C# comes from Jeffrey Richter in his book CLR Via C# . Here are his 3 reasons:

  • I've seen a number of developers confused, not knowing whether to use string or String in their code. Because in C# the string (a keyword) maps exactly to System.String (an FCL type), there is no difference and either can be used.
  • In C#, long maps to System.Int64 , but in a different programming language, long could map to an Int16 or Int32 . In fact, C++/CLI does in fact treat long as an Int32 . Someone reading source code in one language could easily misinterpret the code's intention if he or she were used to programming in a different programming language. In fact, most languages won't even treat long as a keyword and won't compile code that uses it.
  • The FCL has many methods that have type names as part of their method names. For example, the BinaryReader type offers methods such as ReadBoolean , ReadInt32 , ReadSingle , and so on, and the System.Convert type offers methods such as ToBoolean , ToInt32 , ToSingle , and so on. Although it's legal to write the following code, the line with float feels very unnatural to me, and it's not obvious that the line is correct:
BinaryReader br = new BinaryReader(...);
float val  = br.ReadSingle(); // OK, but feels unnatural
Single val = br.ReadSingle(); // OK and feels good

So there you have it. I think these are all really good points. I however, don't find myself using Jeffrey's advice in my own code. Maybe I am too stuck in my C# world but I end up trying to make my code look like the framework code.


There is no difference.

The C# keyword string maps to the .NET type System.String - it is an alias that keeps to the naming conventions of the language.

Similarly, int maps to System.Int32 .


There's a quote on this issue from Daniel Solis' book .

All the predefined types are mapped directly to underlying .NET types. The C# type names (string) are simply aliases for the .NET types (String or System.String), so using the .NET names works fine syntactically, although this is discouraged. Within a C# program, you should use the C# names rather than the .NET names.


Yes, that's no difference between them, just like the bool and Boolean .


This YouTube video demonstrates practically how they differ.

But now for a long textual answer.

When we talk about .NET there are two different things one there is .NET framework and the other there are languages ( C# , VB.NET etc) which use that framework.

" System.String " a.k.a "String" ( capital "S") is a .NET framework data type while "string" is a C# data type.

In short "String" is an alias ( the same thing called with different names) of "string". So technically both the below code statements will give the same output.

String s = "I am String";

or

string s = "I am String";

In the same way there are aliases for other c# data type as shown below:-

object: System.Object , string: System.String , bool: System.Boolean , byte: System.Byte , sbyte: System.SByte , short: System.Int16 and so on

Now the million dollar question from programmer's point of view So when to use "String" and "string"?

First thing to avoid confusion use one of them consistently. But from best practices perspective when you do variable declaration it's good to use "string" ( small "s") and when you are using it as a class name then "String" ( capital "S") is preferred.

In the below code the left hand side is a variable declaration and it declared using "string". At the right hand side we are calling a method so "String" is more sensible.

string s = String.ToUpper() ;

String is not a keyword and it can be used as Identifier whereas string is a keyword and cannot be used as Identifier. And in function point of view both are same.


String stands for System.String and it is a .NET Framework type. string is an alias in the C# language for System.String . Both of them are compiled to System.String in IL (Intermediate Language), so there is no difference. Choose what you like and use that. If you code in C#, I'd prefer string as it's a C# type alias and well-known by C# programmers.

I can say the same about ( int , System.Int32 ) etc..


string and String are identical in all ways (except the uppercase "S"). There are no performance implications either way.

Lowercase string is preferred in most projects due to the syntax highlighting


string is a reserved word, but String is just a class name. This means that string cannot be used as a variable name by itself.

If for some reason you wanted a variable called string , you'd see only the first of these compiles:

StringBuilder String = new StringBuilder();  // compiles
StringBuilder string = new StringBuilder();  // doesn't compile 

If you really want a variable name called string you can use @ as a prefix:

StringBuilder @string = new StringBuilder();

Another critical difference: highlights them differently.


string is just an alias for System.String . The compiler will treat them identically.

The only practical difference is the syntax highlighting as you mention, and that you have to write using System if you use String .


There is one difference - you can't use String without using System; beforehand.







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