compile error about void*

[George2]

Hello everyone,


What is wrong with the code, I just want to allocate an array of 100 void* pointers. :-)

int main()
{
    void** p;
 
    p = new (void*) [100];
 
    return 0;
}
 

>d:\visual studio 2008\projects\test_void1\test_void1\main.cpp(5) : error C2143: syntax error : missing ';' before '['
1>d:\visual studio 2008\projects\test_void1\test_void1\main.cpp(5) : error C3409: empty attribute block is not allowed
1>d:\visual studio 2008\projects\test_void1\test_void1\main.cpp(5) : error C2143: syntax error : missing ']' before 'constant'
1>d:\visual studio 2008\projects\test_void1\test_void1\main.cpp(5) : error C2143: syntax error : missing ';' before 'constant'
1>d:\visual studio 2008\projects\test_void1\test_void1\main.cpp(5) : error C2143: syntax error : missing ';' before ']'
1>d:\visual studio 2008\projects\test_void1\test_void1\main.cpp(5) : error C2143: syntax error : missing ';' before ']'


thanks in advance,
George

[Savage]

You just remove those '()' around void*,and it should compile.

p = new void* [100];

[weaknessforcats]

Use of void* deprecated in C++.

[George2]

Thanks Savage,


Why adding () does not work, which C++ rule is violated?

You just remove those '()' around void*,and it should compile.

p = new void* [100];

regards,
George

[George2]

Why weaknessforcats?


Any links for this topic and using what to replace void*?

Use of void* deprecated in C++.

regards,
George

[Savage]

Thanks Savage,


Why adding () does not work, which C++ rule is violated?




regards,
George

p = new (void*) [100];

this is interpreted by compiler as:

p=(new unknown_type) (void*)[100];

because of new operator precedence.

[weaknessforcats]

p = new (void*) [100];

C++ ain't C.

In C++ new(void*) is a function named new that has a void* arguiment.

Why weaknessforcats?


Any links for this topic and using what to replace void*?

Quote:
Originally Posted by weaknessforcats
Use of void* deprecated in C++.

Function overloading.

[Savage]

C++ ain't C.

In C++ new(void*) is a function named new that has a void* arguiment.



Function overloading.

What about this then:

void foo();
void (**p)();
 
p = new (void (*[3])());
p[0] = f;
 
//etc...

Is this interpreted as a overloaded function called new that takes a pointer to the array of generic function pointers,or does it allocate memory for p?

[George2]

Thanks Savage,


I have tried your code can compile. What does the following statement mean?

p = new (void (*[3])());

what is the type of p? Could you interpret the meaning of right side of assignment and left side of assignment please?

What about this then:

void foo();
void (**p)();
 
p = new (void (*[3])());
p[0] = f;
 
//etc...

Is this interpreted as a overloaded function called new that takes a pointer to the array of generic function pointers,or does it allocate memory for p?

regards,
George

[George2]

Thanks Savage,


Could you explain why the code will be explained to

p=(new unknown_type) (void*)[100];

please?

What is unknown_type comes from? What is new operator precedence?

p = new (void*) [100];

this is interpreted by compiler as:

p=(new unknown_type) (void*)[100];

because of new operator precedence.

regards,
George

[George2]

Yes, weaknessforcats.


I agree "In C++ new(void*) is a function named new that has a void* arguiment", and the global new operator function is invoked.

But, does it has anything to do with my question (compile error)? Could you provide more description please?

C++ ain't C.

In C++ new(void*) is a function named new that has a void* arguiment.



Function overloading.

regards,
George

[weaknessforcats]

I agree "In C++ new(void*) is a function named new that has a void* arguiment", and the global new operator function is invoked.

If you agree that new(void*) is a function named new that has a void argument, then you have answered your own question. You are not allowed to have a function with the same name as a C++ keyword.

[George2]

Thanks weaknessforcats,


In below statements, you mean system global new function?

If you agree that new(void*) is a function named new that has a void argument, then you have answered your own question.

regards,
George

[weaknessforcats]

No I do not.

new is a keyword. You can't use new as a function name.

I think you may confusing the keyword new with the function
operator new() that is called to allocate memory. I'm not making this up. The new operator calls operator new.

[George2]

Thanks weaknessforcats,


Now I understand you mean operator new. :-)

This is what you mentioned before,

--------------------
If you agree that new(void*) is a function named new that has a void argument, then you have answered your own question.
--------------------

Why if I agree I should answer it by myself? I am confused. So, you mean you think in my question the operator new which takes void* as input argument take effect?

No I do not.

new is a keyword. You can't use new as a function name.

I think you may confusing the keyword new with the function
operator new() that is called to allocate memory. I'm not making this up. The new operator calls operator new.

regards,
George

[weaknessforcats]

What the compiler sees is new(void*).

That is a function named new that has a void* argument.

That is an error because new is a reserved C++ keyword.

End of discussion.

[George2]

Thanks for your help, weaknessforcats!


I think when adding (), the placement form of new is invoked, right?

What the compiler sees is new(void*).

That is a function named new that has a void* argument.

That is an error because new is a reserved C++ keyword.

End of discussion.

regards,
George

[weaknessforcats]

That is correct.

char array[1000];
int* arr = new (array) int[5];
 

The int array is allocated inside the char array.

[George2]

Thanks weaknessforcats!


My question is answered.

That is correct.

char array[1000];
int* arr = new (array) int[5];
 

The int array is allocated inside the char array.

regards,
George