A question about constructor function

Quote:

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Originally posted by AnthonyMai

Code:

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class T
{
public:
        int m_i ;
        T () { m_i = 1 ; }
        T(int k ) { this->T::T(); }
};

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Yes it works. You can even add some none-trivial class members like std::string and they will be constructed and then re-constructed, without being destroyed first before re-construction.

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I don't think so . you can check if the variable m_i will is 1 when you create object like T t(2);

I have found the answer from ARM. you can call a constructor with another constructor , but it's useless.

[QUOTE]Originally posted by flysnow

Edit: Totally misguided post. Mai's code may work, but your
mileage may vary depending on your compiler.

Edit: Oh, and the ARM is dated in some areas as it was written
years before the standard was finalized. It does give some
valuable insights, but it can't be taken as gospel in all places.

Quote:

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Yes it works. You can even add some none-trivial class members like std::string and they will be constructed and then re-constructed, without being destroyed first before re-construction.

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Quote:

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I don't think so . you can check if the variable m_i will is 1 when you create object like T t(2);

I have found the answer from ARM. you can call a constructor with another constructor , but it's useless.

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Whether you think so or not is only irrelevant to whether you understand it or not, but not to whether it is actually true or not. The fact is it really works. However I did state in my message that I don't know how some one would find it useful. I personally never needed to do that, but since the OP asked for how to call constructor from constructor, so you get what you asked for.

Any thing is possible.

As I alluded to before, this might not work on your compiler. For
example, Mai's trick does not work on gcc-3.1.1. I get the
following compile-time error:

Quote:

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c++ str_block.cpp -c
str_block.cpp: In constructor `T::T(int)':
str_block.cpp:15: parse error before `;' token
make: 1254-004 The error code from the last command is 1.

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I toyed around with the this->T::T() part of the program and I was
able to get it to compile, but T() was never called [m_i printed out
as garbage on Visual Studio, but 0 on one of my gcc systems].

Thus, use Mai's trick only if you want to enter the uncharted
realm of unportability.

--Paul

Quote:

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Originally posted by PaulWendt
As I alluded to before, this might not work on your compiler. For
example, Mai's trick does not work on gcc-3.1.1. I get the
following compile-time error:


I toyed around with the this->T::T() part of the program and I was
able to get it to compile, but T() was never called [m_i printed out
as garbage on Visual Studio, but 0 on one of my gcc systems].

Thus, use Mai's trick only if you want to enter the uncharted
realm of unportability.

--Paul

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On the Borland C++ Builder 6.0, you get this error:

Quote:

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'T is not a member of 'T'.

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On the Comeau compiler, you get this:

Quote:

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ComeauTest.c", line 6: error: a constructor or destructor may not have its address
taken
T(int k ) { this->T::T(); }
^

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From the ANSI standard 12.1.12:

Quote:

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No return type (not even void) shall be specified for a constructor. A return statement in the body of a
constructor shall not specify a return value. The address of a constructor shall not be taken.

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Regards,

Paul McKenzie

Hey its not my invention to call constructor that way. I actually learned it from CodeGuru.

Quote:

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No return type (not even void) shall be specified for a constructor. A return statement in the body of a
constructor shall not specify a return value. The address of a constructor shall not be taken.

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The address of a constructor shall not be taken by WHO Obviously some one has to take the address of the constructor and actually make the call, or else how would it magically end up jumping into the constructor code.

The address of a constructor is taken at least by one outlaw, the new operator. Actually by two, since the compiler can take the address and call constructor to initialize an object on the stack, too.

Here is the another trick how to call constructor from a constructor:

Code:

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T::T(int k )
{
    new(this) T();
}

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But really, this->T::T(); would be simpler when compiled and the effect is the same.

Quote:

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Originally posted by AnthonyMai
But really, this->T::T(); would be simpler when compiled and the effect is the same.

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Assuming your compiler is Visual Studio, then you're right. If you
use any other compiler out there, don't count on it :)

--Paul