Question

One Book(Object Oriented Programming with C++ by E.Balagurusamy) says that

 const size = 10;  

means

 const int size = 10; 

but g++ compiler (version-4.6.1 in ubuntu) issues an error as

error: ‘size’ does not name a type 

what should I conclude based on this?

1. g++ doesn’t support the feature.
2. It is new feature. Latest g++ version supports it.
3. The statement is wrong. Data-type is mandatory with the const keyword.
4. Something else.

Answer 1

Looks like an error in the book … you definitely must name a type or aliased type (i.e., a typedef) since C++ is a strongly-typed languages.

Here is what the C++03 specification states on objects, declarations and definitions:

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Section 1.8/1:

The properties of an object are determined when the object is created. An object can have a name (clause 3). An object has a storage duration (3.7) which influences its lifetime (3.8). An object has a type (3.9). The term object type refers to the type with which the object is created.

Then in Section 3.1/1:

A declaration is a definition … [note: the rest of the paragraph are exceptions to this rule and are omitted since they’re not applicable in this case]

Then in Section 3.1/6:

A program is ill-formed if the definition of any object gives the object an incomplete type

Finally, in Section 3.9.2/1 it states:

… the term object type (1.8) includes the cv-qualifiers specified when the object is created. The presence of a const specifier in a decl-specifier-seq declares an object of const-qualified object type; such object is called a const object. …

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So according to 3.9.2/1, const is a qualifier, not a type, and as-such, it has to qualify a valid unqualified type. Secondly, in the example given, according to 3.1/1, the declaration of size is also a definition, and therefore the size object must have an associated type or the program is ill-formed according to 3.1/6.