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How to initialize a member struct

P: n/a
Hi all,

If I have a class that includes an instance of a struct as a member, how do
I initialize that struct? I can't find a syntax for the constructor
"initializer list" that works.

For example, suppose MyStruct has 3 int members. I've tried something like
this:

class Test {
private:
MyStruct X
}

// Constructor
Test::Test(void) : X(1,2,3) // Try initializing all 3 struct members...
Nov 29 '07 #1
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3 Replies


P: n/a
Hi Bob,

Using initializer list for another structure member means calling that
structure's constructor. So that structure must has a constructor matching
the signature with the initializer list calling, like this:
struct MyStruct
{
int m_a;
int m_b;
int m_c;

MyStruct(int a, int b, int c)
{
m_a = a;
m_b = b;
m_c = c;
}
};

class Test {
Test::Test(void) : X(1,2,3)
{
}
private:
MyStruct X;
};
Hope it helps.

Best regards,
Jeffrey Tan
Microsoft Online Community Support
==================================================
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==================================================
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Nov 29 '07 #2

P: n/a
If I create a MyStruct in "normal" code, I can just write:
>
MyStruct x = {1, 2, 3};

But I apparently can't include the initializer list (the "{1, 2, 3}") in a
class definition header file where I declare a member variable of type
MyStruct. This leaves me with trying to come up with a way to initialize
the struct in the class constructor. The ugly way to do this is to
explicitly initialize each member of the structure in the constructor
code. But I'm looking for a way to use an initializer list to initialize
the entire struct all at once.
With a helper function:

static MyStruct init_my_struct(int a, int b, int c)
{
const MyStruct x = { a, b, c };
return x;
}

MyConstructor() : member(init_my_struct(1, 2, 3)) {}

Sigh... I told you it was complicated...
>
""Jeffrey Tan[MSFT]"" <je***@online.microsoft.comwrote in message
news:XU*************@TK2MSFTNGHUB02.phx.gbl...
>Hi Bob,

Using initializer list for another structure member means calling that
structure's constructor. So that structure must has a constructor
matching
the signature with the initializer list calling, like this:
struct MyStruct
{
int m_a;
int m_b;
int m_c;

MyStruct(int a, int b, int c)
{
m_a = a;
m_b = b;
m_c = c;
}
};

class Test {
Test::Test(void) : X(1,2,3)
{
}
private:
MyStruct X;
};
Hope it helps.

Best regards,
Jeffrey Tan
Microsoft Online Community Support
================================================= =
Get notification to my posts through email? Please refer to
http://msdn.microsoft.com/subscripti...ult.aspx#notif
ications.

Note: The MSDN Managed Newsgroup support offering is for non-urgent
issues
where an initial response from the community or a Microsoft Support
Engineer within 1 business day is acceptable. Please note that each
follow
up response may take approximately 2 business days as the support
professional working with you may need further investigation to reach the
most efficient resolution. The offering is not appropriate for situations
that require urgent, real-time or phone-based interactions or complex
project analysis and dump analysis issues. Issues of this nature are best
handled working with a dedicated Microsoft Support Engineer by contacting
Microsoft Customer Support Services (CSS) at
http://msdn.microsoft.com/subscripti...t/default.aspx.
================================================= =
This posting is provided "AS IS" with no warranties, and confers no
rights.



Nov 29 '07 #3

P: n/a
Thanks Ben. I guess that's about as clean a solution as I'm likely to get.

- Bob

"Ben Voigt [C++ MVP]" <rb*@nospam.nospamwrote in message
news:uG****************@TK2MSFTNGP04.phx.gbl...
>If I create a MyStruct in "normal" code, I can just write:

MyStruct x = {1, 2, 3};

But I apparently can't include the initializer list (the "{1, 2, 3}") in
a class definition header file where I declare a member variable of type
MyStruct. This leaves me with trying to come up with a way to initialize
the struct in the class constructor. The ugly way to do this is to
explicitly initialize each member of the structure in the constructor
code. But I'm looking for a way to use an initializer list to initialize
the entire struct all at once.

With a helper function:

static MyStruct init_my_struct(int a, int b, int c)
{
const MyStruct x = { a, b, c };
return x;
}

MyConstructor() : member(init_my_struct(1, 2, 3)) {}

>Sigh... I told you it was complicated...
>>
""Jeffrey Tan[MSFT]"" <je***@online.microsoft.comwrote in message
news:XU*************@TK2MSFTNGHUB02.phx.gbl...
>>Hi Bob,

Using initializer list for another structure member means calling that
structure's constructor. So that structure must has a constructor
matching
the signature with the initializer list calling, like this:
struct MyStruct
{
int m_a;
int m_b;
int m_c;

MyStruct(int a, int b, int c)
{
m_a = a;
m_b = b;
m_c = c;
}
};

class Test {
Test::Test(void) : X(1,2,3)
{
}
private:
MyStruct X;
};
Hope it helps.

Best regards,
Jeffrey Tan
Microsoft Online Community Support
================================================ ==
Get notification to my posts through email? Please refer to
http://msdn.microsoft.com/subscripti...ult.aspx#notif
ications.

Note: The MSDN Managed Newsgroup support offering is for non-urgent
issues
where an initial response from the community or a Microsoft Support
Engineer within 1 business day is acceptable. Please note that each
follow
up response may take approximately 2 business days as the support
professional working with you may need further investigation to reach
the
most efficient resolution. The offering is not appropriate for
situations
that require urgent, real-time or phone-based interactions or complex
project analysis and dump analysis issues. Issues of this nature are
best
handled working with a dedicated Microsoft Support Engineer by
contacting
Microsoft Customer Support Services (CSS) at
http://msdn.microsoft.com/subscripti...t/default.aspx.
================================================ ==
This posting is provided "AS IS" with no warranties, and confers no
rights.




Nov 29 '07 #4

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