Calling a struct constructor in a class constructor body

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Karl M - 18 Dec 2004 13:21 GMT

Hi C++ experts!
Definitely I skipped C/C++ 101 because I have this pitfall:
I need to call the struct ctor in the class default ctor body see below:

//Some.h
struct MyStruct
{
int a[5];
//etc
};
class MyClass
{
public:
MyClass();
~MyClass();
//etc
protected:
//etc
MyStruct m_MyStruct;
//etc
};

//some.cpp
#include "some.h"
MyClass::MyClass() : m_MyStruct()
/* default ctor of the struct with NULL- it works but not with the order of
class member declarations I have, so...*/
{
/* here I need to have m_MyStruct() initialized with NULL, not
using m_MyStruct.a[1] = 0; etc
How? Or maybe m_MyStruct = MyStruct(); Is this correct? It init NULL
m_MyStruct
but uses a local stack var MyStruct() - stupid*/
}

Thank you
Karl

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Ashok K Kumar - 23 Dec 2004 13:00 GMT

Hi,

It not clear what you wish to achieve. But Let me take a guess. You want to
initialize all the members of the struct to 0. There are two ways.
a) Have a ctor for MyStruct and initialize it 0. This will
initialize all the members to null when an object of the struct is created.
struct MyStruct
{
int a[5];
//other members
//etc.....

//stuct ctor
MyStruct()
{
ZeroMemory(this,sizeof(MyStruct)); // or use
memset
}
};
b) Call Zeromemory or memset in the ctor of the class to set all the
members of the struct to null
MyClass::MyClass()
{
ZeroMemory(&m_MyStruct, sizeof(MyStruct));
}

HTH

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_____________________
Ashok K Kumar
ashokkal at gmail dot com

> Hi C++ experts!
> Definitely I skipped C/C++ 101 because I have this pitfall:
[quoted text clipped - 34 lines]
> Thank you
> Karl

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Karl M - 26 Dec 2004 03:37 GMT

Hi Ashok,
I guess I was not very explicit with my message:
I was hoping that there is a way to call the "default" constructor for a
structure inside the class constructor body.
Again, if you don't define a constructor for a struct and define the class
constructor like:
MyClass::MyClass() : m_MyStruct() {}
the compiler generate the underlying struct ctor code that init with NULL
the struct members not using any RTL ZeroMemory or any other calls but just
using push 5; pop ecx; rep stos [m_MyStruct].
Regards,
Karl

> Hi,
>
[quoted text clipped - 61 lines]
> > Thank you
> > Karl

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Calling a struct constructor in a class constructor body

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