I have come accross a piece of C++ code with the construct:
MyClass *c = new class MyClass();
Is there a difference between this and:
MyClass *c = new MyClass();
?
Thank you. 6 2516
"dpr" <vi********@vir tualway.com.br> wrote in message
news:c0******** **@news-reader4.wanadoo .fr...
| I have come accross a piece of C++ code with the construct:
|
| MyClass *c = new class MyClass();
|
| Is there a difference between this and:
|
| MyClass *c = new MyClass();
|
| ?
No.
Actually, this is not about "new" and "new class",
but about "MyClass" or "class MyClass".
In C compilers, identifiers that refer to a struct or union
need to be explicitly prefixed with the corresponding keyword:
struct Test { int x,y; };
int f( Test a ); // Error in C, ok in C++
int f( struct Test a ); // ok in C and C++
For the sake of consistency and backwards-compatibility,
C++ allows both ways for referring to a struct, union, or class:
you can also write "class MyClass" to refer to "MyClass".
hth, Ivan
-- http://ivan.vecerina.com/contact/?subject=NG_POST <- e-mail contact form
On Thu, 12 Feb 2004 12:25:17 +0100, "Ivan Vecerina" <se*********@ve cerina.com> wrote: In C compilers, identifiers that refer to a struct or union need to be explicitly prefixed with the corresponding keyword: struct Test { int x,y; }; int f( Test a ); // Error in C, ok in C++ int f( struct Test a ); // ok in C and C++
For the sake of consistency and backwards-compatibility, C++ allows both ways for referring to a struct, union, or class: you can also write "class MyClass" to refer to "MyClass".
Just a little point: equivalent ways mostly, but not always.
In a friend declaration of a class the word "class" or "struct"
is mandatory.
Pitfall: g++ 2.95 accepts code that omits "class" or struct".
Ivan Vecerina wrote: "dpr" <vi********@vir tualway.com.br> wrote in message news:c0******** **@news-reader4.wanadoo .fr... | I have come accross a piece of C++ code with the construct: | | MyClass *c = new class MyClass(); | | Is there a difference between this and: | | MyClass *c = new MyClass(); | | ? No.
Actually, this is not about "new" and "new class", but about "MyClass" or "class MyClass".
There is a difference. The latter one declares MyClass as a class, the
former doesn't. So this will compile:
int main()
{
class X* p;
}
class X
{
};
while this won't:
int main()
{
X* p;
}
class X
{
};
However, since (AFAIK) the class must be fully defined when using new,
that difference is not noticable in the OP's code.
Ivan Vecerina wrote: "dpr" <vi********@vir tualway.com.br> wrote in message news:c0******** **@news-reader4.wanadoo .fr...
In C compilers, identifiers that refer to a struct or union need to be explicitly prefixed with the corresponding keyword: struct Test { int x,y; }; int f( Test a ); // Error in C, ok in C++ int f( struct Test a ); // ok in C and C++
For the sake of consistency and backwards-compatibility, C++ allows both ways for referring to a struct, union, or class: you can also write "class MyClass" to refer to "MyClass".
A class may be hidden by a variable, e.g.:
class X {};
int main() {
int X;
X x; // Doesn't compile, class X is hidden
class X x; // But this works.
}
Christoph
"Rolf Magnus" <ra******@t-online.de> wrote in message
news:c0******** *****@news.t-online.com... Ivan Vecerina wrote:
"dpr" <vi********@vir tualway.com.br> wrote in message news:c0******** **@news-reader4.wanadoo .fr... | I have come accross a piece of C++ code with the construct: | | MyClass *c = new class MyClass(); | | Is there a difference between this and: | | MyClass *c = new MyClass(); | | ? No.
Actually, this is not about "new" and "new class", but about "MyClass" or "class MyClass".
There is a difference. The latter one declares MyClass as a class, the former doesn't. So this will compile:
int main() { class X* p; }
class X { };
while this won't:
int main() { X* p; }
class X { };
However, since (AFAIK) the class must be fully defined when using new, that difference is not noticable in the OP's code.
Rolf, you mean something like forward declaration? As if:
class X;
int main()
{
X *p;
}
class X
{
};
--
Elias
lallous wrote: "Rolf Magnus" <ra******@t-online.de> wrote in message news:c0******** *****@news.t-online.com... Ivan Vecerina wrote:
> "dpr" <vi********@vir tualway.com.br> wrote in message > news:c0******** **@news-reader4.wanadoo .fr... > | I have come accross a piece of C++ code with the construct: > | > | MyClass *c = new class MyClass(); > | > | Is there a difference between this and: > | > | MyClass *c = new MyClass(); > | > | ? > No. > > Actually, this is not about "new" and "new class", > but about "MyClass" or "class MyClass".
There is a difference. The latter one declares MyClass as a class, the former doesn't. So this will compile:
int main() { class X* p; }
class X { };
while this won't:
int main() { X* p; }
class X { };
However, since (AFAIK) the class must be fully defined when using new, that difference is not noticable in the OP's code. Rolf, you mean something like forward declaration? As if:
class X; int main() { X *p; } class X { };
Exactly. This thread has been closed and replies have been disabled. Please start a new discussion. Similar topics |
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