It's common in C++ to name member variables with some kind of prefix to denote the fact that they're member variables, rather than local variables or parameters. If you've come from an MFC background, you'll probably use m_foo. I've also seen myFoo occasionally.
C# (or possibly just .NET) seems to recommend using just an underscore, as in _foo. Is this allowed by the C++ standard?
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As for the other part of the question, it's common to put the underscore at the end of the variable name to not clash with anything internal.
I do this even inside classes and namespaces because I then only have to remember one rule (compared to "at the end of the name in global scope, and the beginning of the name everywhere else").
From MSDN:
Use of two sequential underscore characters ( __ ) at the beginning of 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.
This means that you can use a single underscore as a member variable prefix, as long as it's followed by a lower-case letter.
This is apparently taken from section 17.4.3.1.2 of the C++ standard, but I can't find an original source for the full standard online.
See also this question.
The rules to avoid collision of names are both in the C++ standard (see Stroustrup book) and mentioned by C++ gurus (Sutter, etc.).
Because I did not want to deal with cases, and wanted a simple rule, I have designed a personal one that is both simple and correct:
When naming a symbol, you will avoid collision with compiler/OS/standard libraries if you:
Of course, putting your code in an unique namespace helps to avoid collision, too (but won't protect against evil macros)
(I use macros because they are the more code-polluting of C/C++ symbols, but it could be anything from variable name to class name)
#define _WRONG
#define __WRONG_AGAIN
#define RIGHT_
#define WRONG__WRONG
#define RIGHT_RIGHT
#define RIGHT_x_RIGHT
From the n3242.pdf file (I expect the final standard text to be similar):
17.6.3.3.2 Global names [global.names]
Certain sets of names and function signatures are always reserved to the implementation:
— Each name that contains a double underscore _ _ or begins with an underscore followed by an uppercase letter (2.12) is reserved to the implementation for any use.
— Each name that begins with an underscore is reserved to the implementation for use as a name in the global namespace.
But also:
17.6.3.3.5 User-defined literal suffixes [usrlit.suffix]
Literal suffix identifiers that do not start with an underscore are reserved for future standardization.
This last clause is confusing, unless you consider that a name starting with one underscore and followed by a lowercase letter would be Ok if not defined in the global namespace...
As for the other part of the question, it's common to put the underscore at the end of the variable name to not clash with anything internal.
I do this even inside classes and namespaces because I then only have to remember one rule (compared to "at the end of the name in global scope, and the beginning of the name everywhere else").
The rules to avoid collision of names are both in the C++ standard (see Stroustrup book) and mentioned by C++ gurus (Sutter, etc.).
Because I did not want to deal with cases, and wanted a simple rule, I have designed a personal one that is both simple and correct:
When naming a symbol, you will avoid collision with compiler/OS/standard libraries if you:
Of course, putting your code in an unique namespace helps to avoid collision, too (but won't protect against evil macros)
(I use macros because they are the more code-polluting of C/C++ symbols, but it could be anything from variable name to class name)
#define _WRONG
#define __WRONG_AGAIN
#define RIGHT_
#define WRONG__WRONG
#define RIGHT_RIGHT
#define RIGHT_x_RIGHT
From the n3242.pdf file (I expect the final standard text to be similar):
17.6.3.3.2 Global names [global.names]
Certain sets of names and function signatures are always reserved to the implementation:
— Each name that contains a double underscore _ _ or begins with an underscore followed by an uppercase letter (2.12) is reserved to the implementation for any use.
— Each name that begins with an underscore is reserved to the implementation for use as a name in the global namespace.
But also:
17.6.3.3.5 User-defined literal suffixes [usrlit.suffix]
Literal suffix identifiers that do not start with an underscore are reserved for future standardization.
This last clause is confusing, unless you consider that a name starting with one underscore and followed by a lowercase letter would be Ok if not defined in the global namespace...
Yes, underscores may be used anywhere in an identifier. I believe the rules are: any of a-z, A-Z, _ in the first character and those +0-9 for the following characters.
Underscore prefixes are common in C code -- a single underscore means "private", and double underscores are usually reserved for use by the compiler.
From MSDN:
Use of two sequential underscore characters ( __ ) at the beginning of 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.
This means that you can use a single underscore as a member variable prefix, as long as it's followed by a lower-case letter.
This is apparently taken from section 17.4.3.1.2 of the C++ standard, but I can't find an original source for the full standard online.
See also this question.
Yes, underscores may be used anywhere in an identifier. I believe the rules are: any of a-z, A-Z, _ in the first character and those +0-9 for the following characters.
Underscore prefixes are common in C code -- a single underscore means "private", and double underscores are usually reserved for use by the compiler.
As for the other part of the question, it's common to put the underscore at the end of the variable name to not clash with anything internal.
I do this even inside classes and namespaces because I then only have to remember one rule (compared to "at the end of the name in global scope, and the beginning of the name everywhere else").
From MSDN:
Use of two sequential underscore characters ( __ ) at the beginning of 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.
This means that you can use a single underscore as a member variable prefix, as long as it's followed by a lower-case letter.
This is apparently taken from section 17.4.3.1.2 of the C++ standard, but I can't find an original source for the full standard online.
See also this question.
Yes, underscores may be used anywhere in an identifier. I believe the rules are: any of a-z, A-Z, _ in the first character and those +0-9 for the following characters.
Underscore prefixes are common in C code -- a single underscore means "private", and double underscores are usually reserved for use by the compiler.
The rules to avoid collision of names are both in the C++ standard (see Stroustrup book) and mentioned by C++ gurus (Sutter, etc.).
Because I did not want to deal with cases, and wanted a simple rule, I have designed a personal one that is both simple and correct:
When naming a symbol, you will avoid collision with compiler/OS/standard libraries if you:
Of course, putting your code in an unique namespace helps to avoid collision, too (but won't protect against evil macros)
(I use macros because they are the more code-polluting of C/C++ symbols, but it could be anything from variable name to class name)
#define _WRONG
#define __WRONG_AGAIN
#define RIGHT_
#define WRONG__WRONG
#define RIGHT_RIGHT
#define RIGHT_x_RIGHT
From the n3242.pdf file (I expect the final standard text to be similar):
17.6.3.3.2 Global names [global.names]
Certain sets of names and function signatures are always reserved to the implementation:
— Each name that contains a double underscore _ _ or begins with an underscore followed by an uppercase letter (2.12) is reserved to the implementation for any use.
— Each name that begins with an underscore is reserved to the implementation for use as a name in the global namespace.
But also:
17.6.3.3.5 User-defined literal suffixes [usrlit.suffix]
Literal suffix identifiers that do not start with an underscore are reserved for future standardization.
This last clause is confusing, unless you consider that a name starting with one underscore and followed by a lowercase letter would be Ok if not defined in the global namespace...
Yes, underscores may be used anywhere in an identifier. I believe the rules are: any of a-z, A-Z, _ in the first character and those +0-9 for the following characters.
Underscore prefixes are common in C code -- a single underscore means "private", and double underscores are usually reserved for use by the compiler.
From MSDN:
Use of two sequential underscore characters ( __ ) at the beginning of 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.
This means that you can use a single underscore as a member variable prefix, as long as it's followed by a lower-case letter.
This is apparently taken from section 17.4.3.1.2 of the C++ standard, but I can't find an original source for the full standard online.
See also this question.
Source: Stackoverflow.com