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- C Identifiers What is Identifier? An identifier is a name that identifies unique things. Here things may be a person, object, idea or anything. The following diagram clearly represents the concept of identifier. Identifiers In C. Identifier as the name suggest are used identify elements in C Programming.
In C, C++, C# and other programming languages, an identifier is a name that is assigned by the user for a program element such as variable, type, template, class, function or namespace. It is usually limited to letters, digits, and underscores. Certain words, such as 'new,' 'int' and 'break,' are reserved keywords and cannot be used as identifiers. Identifiers are used to identify a program element in the code.
Sets the decimal precision to be used to format floating-point values on output operations. Behaves as if member precision were called with n as argument on the stream on which it is inserted/extracted as a manipulator (it can be inserted/extracted on input streams or output streams). This manipulator is declared in header. Parameters n New value for the.
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Computer languages have restrictions for which characters can appear in an identifier. For example, in early versions of the C and C++ languages, identifiers were restricted to a sequence of one or more ASCII letters, digits, which may not appear as the first character, and underscores. Later versions of these languages support almost all Unicode characters in an identifier with the exception of white space characters and language operators.
You designate an identifier by declaring it early in the code. Then, you can use that identifier later in the program to refer to the value you assigned to the identifier.
Rules for Identifiers
When naming an identifier, follow these established rules:
- An identifier cannot be a C# keyword. Keywords have predefined special meanings to the compiler.
- It cannot have two consecutive underscores.
- It can be a combination of numbers, letters, connectors, and Unicode characters.
- It must start with a letter of the alphabet or an underscore, not a number.
- It should not include white space.
- It cannot have more than 511 characters.
- It has to be declared before it is referred.
- Two identifiers cannot have the same name.
- Identifiers are case sensitive.
For implementations of programming languages that are compiled, identifiers are often only compile-time entities. That is, at run time the compiled program contains references to memory addresses and offsets rather than the textual identifier tokens—these memory addresses or offsets having been assigned by the compiler to each identifier.
Verbatim Identifiers
Adding the prefix '@' to a keyword enables the keyword, which is normally reserved, to be used as an identifier, which can be useful when interfacing with other programming languages. The @ is not considered part of the identifier, so it might not be recognized in some languages. It is a special indicator to not treat what comes after it as a keyword, but rather as an identifier. This type of identifier is called a verbatim identifier. Using verbatim identifiers is allowed but strongly discouraged as a matter of style.
-->An identifier is a sequence of characters used to denote one of the following:
Object or variable name
Class, structure, or union name
Enumerated type name
Member of a class, structure, union, or enumeration
Function or class-member function
typedef name
Label name
Macro name
Macro parameter
The following characters are allowed as any character of an identifier:
Certain ranges of universal character names are also allowed in an identifier. A universal character name in an identifier cannot designate a control character or a character in the basic source character set. For more information, see Character Sets. These Unicode code point number ranges are allowed as universal character names for any character in an identifier:
- 00A8, 00AA, 00AD, 00AF, 00B2-00B5, 00B7-00BA, 00BC-00BE, 00C0-00D6, 00D8-00F6, 00F8-00FF, 0100-02FF, 0370-167F, 1681-180D, 180F-1DBF, 1E00-1FFF, 200B-200D, 202A-202E, 203F-2040, 2054, 2060-206F, 2070-20CF, 2100-218F, 2460-24FF, 2776-2793, 2C00-2DFF, 2E80-2FFF, 3004-3007, 3021-302F, 3031-303F, 3040-D7FF, F900-FD3D, FD40-FDCF, FDF0-FE1F, FE30-FE44, FE47-FFFD, 10000-1FFFD, 20000-2FFFD, 30000-3FFFD, 40000-4FFFD, 50000-5FFFD, 60000-6FFFD, 70000-7FFFD, 80000-8FFFD, 90000-9FFFD, A0000-AFFFD, B0000-BFFFD, C0000-CFFFD, D0000-DFFFD, E0000-EFFFD
The following characters are allowed as any character in an identifier except the first:
These Unicode code point number ranges are also allowed as universal character names for any character in an identifier except the first:
- 0300-036F, 1DC0-1DFF, 20D0-20FF, FE20-FE2F
Microsoft Specific
Only the first 2048 characters of Microsoft C++ identifiers are significant. Names for user-defined types are 'decorated' by the compiler to preserve type information. The resultant name, including the type information, cannot be longer than 2048 characters. (See Decorated Names for more information.) Factors that can influence the length of a decorated identifier are:
Whether the identifier denotes an object of user-defined type or a type derived from a user-defined type.
Whether the identifier denotes a function or a type derived from a function.
The number of arguments to a function.
The dollar sign $ is a valid identifier character in the Microsoft C++ compiler (MSVC). MSVC also allows you to use the actual characters represented by the allowed ranges of universal character names in identifiers. To use these characters, you must save the file by using a file encoding codepage that includes them. This example shows how both extended characters and universal character names can be used interchangeably in your code.
The range of characters allowed in an identifier is less restrictive when compiling C++/CLI code. Identifiers in code compiled by using /clr should follow Standard ECMA-335: Common Language Infrastructure (CLI).
END Microsoft Specific
The first character of an identifier must be an alphabetic character, either uppercase or lowercase, or an underscore ( _ ). Because C++ identifiers are case sensitive, fileName is different from FileName.
Identifiers cannot be exactly the same spelling and case as keywords. Identifiers that contain keywords are legal. For example, Pint is a legal identifier, even though it contains int, which is a keyword.
Dev C Identifier Number
Use of two sequential underscore characters ( __ ) in an identifier, or a single leading underscore followed by a capital letter, is reserved for C++ implementations in all scopes. You should avoid using one leading underscore followed by a lowercase letter for names with file scope because of possible conflicts with current or future reserved identifiers.