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c++virtualkeywordfunction-declaration
Ronald McBean
Ronald McBean

Reputation: 1427

Does the position of the virtual keyword in a function declaration matter?

Does it make any difference whether I place the virtual keyword in a function declaration before or after the return value type?

virtual void DoSomething() = 0;
void virtual DoSomething() = 0;

I found the void virtual syntax while refactoring some legacy code, and was wondering that it is compiling at all.

Upvotes: 4

Views: 617

Answers (4)

Alok Save
Alok Save

Reputation: 206606

Both the formats work but the standard specifys the first format.

Reference:
C++03 7.1 Specifiers

The specifiers that can be used in a declaration are

   decl-specifier:
         storage-class-specifier
         type-specifier
         function-specifier
         friend
         typedef

     decl-specifier-seq:
           decl-specifier-seqopt decl-specifier

And further function-specifier are explained in,

7.1.2 Function specifiers

Function-specifiers can be used only in function declarations.

 function-specifier:
     inline
     virtual
     explicit

Upvotes: 1

Stefan Birladeanu
Stefan Birladeanu

Reputation: 294

tested just now:

compiles both ways.

usualy virtual is put before return type.

read more here: http://msdn.microsoft.com/en-us/library/0y01k918%28v=vs.80%29.aspx

Upvotes: -1

iammilind
iammilind

Reputation: 70078

Both the statements are equivalent.
But the 1st one is more conventional. Because, generally mandatory fields are kept closest to any syntax (i.e. the function prototype in your example).

virtual is an optional keyword (it's needed for pure virtual though). However return type (here void) is a mandatory keyword, which is always required. So people keep virtual on the left most side and the return type a little closer to the function signature.

Another example: I generally see that in below code 1st syntax is more popular for the same reason:

const int i = 0;  // 1
int const i = 0;  // 2

Upvotes: 5

Nikola Smiljanić
Nikola Smiljanić

Reputation: 26863

There is no difference between the two, C++ grammar allows virtual keyword to appear both before and after return type. It's just common practice to place it first in the declaration.

Upvotes: 3

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