Re: STL map of structures
- From: changliw@xxxxxxxxxxxxxxxxxxxx ("Charles Wang [MSFT]")
- Date: Thu, 15 May 2008 08:05:18 GMT
Hi Bob,
I believe that Doug had provided concise and helpful answers here. I just
would like to add additional comments regarding one of your concerns, "The
downside (such as it is) of having a map of structures is having
to add a default constructor and a copy constructor to my structure.".
Generally you need not to add a default constructor and a copy constructor
to your structure since complier will do it implicitly (mostly bitwise
copy). You can simply perform a test with the following code:
struct MyStruct
{
int m_i;
int* p_i;
};
int _tmain(int argc, _TCHAR* argv[])
{
MyStruct s;
int n = 100;
s.m_i = 10;
s.p_i = &n;
map<int, MyStruct> myMap;
myMap[0]=s;
printf("%d,%d",myMap[0].m_i,*(myMap[0].p_i));
getchar();
return 0;
}
Whether or not to use a copy constructor depends on situations. When a
class does not allow/need to use bitwise copy semantics, you need to
explicitly write a copy constructor. I would like to recommend a famous
book (written by Stanley B.Lippman) for you "Inside The C++ Object Model"
(http://www.amazon.com/Inside-Object-Model-Stanley-Lippman/dp/0201834545).
You can read the chapter "The senmantics of constructors" in which Stanley
listed four typical situations that do not need "Bitwise Copy Semantics".
Generally they are the following:
1) Member class object having copy constructor
2) Base class having copy constructor
3) Class having one or more virtual functions
4) Derived class having one or more virtual base classes
Hope this helps.
Best regards,
Charles Wang
Microsoft Online Community Support
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