It is a degenerate syntax that is allowed but provides no benefit. Most modern compilers can be provoked into emitting a warning about it; by default, they may not. Without the typedef name, the keyword typedef is superfluous; in your example, it is completely equivalent to: enum test { one }; Another place where it …
It’s good. It’s legal and localized.
Here is what Bjarne Stroustrup says about why they introduced using instead of extending typedef: The keyword using is used to get a linear notation “name followed by what it refers to.” We tried with the conventional and convoluted typedef solution, but never managed to get a complete and coherent solution until we settled on …
There is now NS_ENUM starting Xcode 4.5: typedef NS_ENUM(NSUInteger, NSCellType) { NSNullCellType = 0, NSTextCellType = 1, NSImageCellType = 2 }; And you can consider NS_OPTIONS if you work with binary flags: typedef NS_OPTIONS(NSUInteger, MyCellFlag) { MyTextCellFlag = 1 << 0, MyImageCellFlag = 1 << 1, };
Basically a typedef has exactly the same syntax as an object declaration except that it is prefixed with typedef. Doing that changes the meaning of the declaration so that the new identifier declares an alias for the type that the object that would have been declared, had it been a normal declaration, would have had. …
It’s the same as typedef int foo; i.e. it defines foo to be the type int. While the grammar allows to swap typedef and int in this case, you usually would not do this because it impairs readability.
It documents your intent – you will be storing small numbers, rather than a character. Also it looks nicer if you’re using other typedefs such as uint16_t or int32_t.
They are equivalent, from the standard (emphasis mine) (7.1.3.2): A typedef-name can also be introduced by an alias-declaration. The identifier following the using keyword becomes a typedef-name and the optional attribute-specifier-seq following the identifier appertains to that typedef-name. It has the same semantics as if it were introduced by the typedef specifier. In particular, it …
Absolutely valid. Usually, you can take full advantage of this way by defining two types together: typedef struct { int a; int b; } S1, *S1PTR; Where S1 is a struct and S1PTR is the pointer to this struct.
type *type; // why is it allowed? C++11 3.3.2/1 says: The point of declaration for a name is immediately after its complete declarator (Clause 8) and before its initializer (if any) So the variable name type is not introduced until after the use of the type name type; the type name is the only available …