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I did a search for this question thinking that somebody must have asked it before. I did not turn up any results, so if it has been, please post the link and feel free to close the question.
I ran across this code in EASTL:
enum : size_type { // size_type = size_t
npos = (size_type)-1,
kMaxSize = (size_type)-2
};
I have never encountered an enum declaration like that. What does the : do in this case?
730
There are three distinct usages of a colon in the declaration of a class. The third is to use generic constraints (happens at a different place but still in declaration) There are two colons used in class declarations. The most common one denotes inheritance:
Following is an example of enum declaration. // The name of enumeration is "flag" and the constant // are the values of the flag. By default, the values // of the constants are as follows: // constant1 = 0, constant2 = 1, constant3 = 2 and // so on. enum flag {constant1, constant2, constant3, ....... };
It is mainly used to assign names to integral constants, the names make a program easy to read and maintain. The keyword ‘enum’ is used to declare new enumeration types in C and C++. Following is an example of enum declaration. // The name of enumeration is "flag" and the constant // are the values of the flag.
Last Updated : 21 Dec, 2018. Enumeration (or enum) is a user defined data type in C. It is mainly used to assign names to integral constants, the names make a program easy to read and maintain. enum State {Working = 1, Failed = 0}; The keyword ‘enum’ is used to declare new enumeration types in C and C++.
In C++0x, you can specify the underlying type for the enum. In this case, it will be size_type.
(And it may be supported as an extension in other places prior to C++0x, obviously.)
119
This is a Microsoft extension that lets you choose the base type of the enum values. For example, this lets you specify that values are unsigned (Microsoft's compilers usually choose signed by default) or that they only occupy 8 or 16 bits (Microsoft normally defaults to 32 bits).
The syntax is documented here: http://msdn.microsoft.com/en-us/library/2dzy4k6e(v=VS.100).aspx but I'm not able to find official documentation of what it actually does.
C++11 adds a similar feature, but with slightly different syntax. In C++11 you'd write it like this:
enum MyEnum : size_type { .. values .. };
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