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From: feng chen <fchen@fas.harvard.edu>
Subject: Re: valid code?
Date: 2000/03/21
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Ron Natalie <ron@sensor.com> wrote:

Seems it requires a default constructor for both A and B. Check the output
of the following program:

#include <stdio.h>

struct A {
        A() {v=0; printf("default A\n");}
        explicit A(int i) {v=i; printf("explicit A\n");}
int v;
};

struct B {
A v;
        B() {printf("default B\n");}
        B(A const &j) {v=j; printf("non-default B\n");}
};

struct C {
B v;
        C(B const &k) {v=k; printf("In C\n");}
};

int main()
{
        C c(B(A(1)));
        return 1;
}


The output is:
explicit A
default A
non-default B
default A
default B
In C

Both default A and default B constructors are called in the
process. And seems GNU C++ doesn't provide default constructor. :)


Feng Chen
fchen@fas.harvard.edu


: Ulf Larsson wrote:

:> g++-2.95.2 tells me that
:> 
:> prog.cc: In function `void f()':
:> prog.cc:19: no matching function for call to `B::B (int)'
:> prog.cc:8: candidates are: B::B(const A &)
:> prog.cc:9:                 B::B(const B &)
:> 
:> This doesn't make sense to me.
: ]
: Doesn't make sense to me either.

: Works fine in egcs 2.91.57 (and the Spar Compiler 5.0)

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