whats the deal with _ATL_CSTRING_EXPLICIT_CONSTRUCTORS

[IndikaNiva]

Do we really need the macro that vc 7 put in to its stdafx.h file.
_ATL_CSTRING_EXPLICIT_CONSTRUCTORS

I would like to know if not having this is a performance hit or not and what are the pros and cons for this macro.

Thank you all.

IK

[marten_range]

ATL_CSTRING_EXPLICIT_CONSTRUCTORS

Makes certain CString constructors explicit, preventing any unintentional conversions

In C++ it means that the constructors are declared something like below:

struct my_string
{
    explicit my_string(char const * const);
};


void f(my_string const & s);

int main()
{
    f(my_string("Test")); // 1. works
    f("Test"); // 2. doesn't work because of explicit
}

If you leave out explicit it means that for 2. above the compiler could implicitly construct a my_string object from the c-string and the code above would compile.

Performance wise it's no difference between 1. and 2. However, in practice by allowing implicit constructors a programmer not aware of the implicit constructors might create unnecessary objects.

Personally I prefer explicit constructors as in my opinion it leads to more robust code (you have to specify what you want) but I admit I'm occassionally tempted by the lures of convenience promised by the implicit constructors.

Hope this helps,

Mårten

[Siddhartha]

I would like to know if not having this is a performance hit or not and what are the pros and cons for this macro.

Looking up MSDN always helps.

• _ATL_CSTRING_EXPLICIT_CONSTRUCTORS

This macro results in CString being explicitly constructed.

• Explicit Constructors

Do we really need the macro that vc 7 put in to its stdafx.h file.

VC++ defines many macros that affect your build.

If I were you, I wouldn't tamper them...

[IndikaNiva]

Well I have given this booooring task of converting like 60 COM DLL projects to unicode.
So I figure if I put this macro in it will generate compiler errors for strings taht dont have _T or L in unicode.

But I find out that in regualr debug this macro will generate an error for
BSTR bsTest = SysAllocString(_T("blah");

CString szString = bsTest // Error.

So I'm just exploring my options here.

Thanks for the input

[Siddhartha]

But I find out that in regualr debug this macro will generate an error for
BSTR bsTest = SysAllocString(_T("blah");

CString szString = bsTest // Error.

I told you already in this thread that CString can wrap LPTSTR from both Unicode and Non-Unicode source strings using overloaded constructors in CStringT - the template class it specializes.

With _ATL_CSTRING_EXPLICIT_CONSTRUCTORS defined, the correct way would be -

CString szString ("blah");

Note that you dont need to do the SysAllocString stuff.

When there are simple ways to do something, I am not able to understand why you try the far-fetched?

Besides, if you are insistent on using this -

CString szString = bsTest;

...Comment out the macro defined in StdAfx.h

However, I prefer the former method that does not require exclusion of this macro.