I have a problem regarding the precedence of overloaded cast operators.
My program is as follows:
#include <stdio.h>
class A;
class B {
public:
B(A &a) {
printf("constru ct\n");
}
};
class A {
public:
B f() {
printf("f\n");
return(B(*this) );
}
operator B () {
printf("convert \n");
return(f());
}
};
int main() {
A a;
a.f();
return(0);
}
When I compile and run the program on Linux using g++, the output is:
f
construct
This is pretty much what I'd expect. However, when I do the same on a
HP-UX system using aCC, the output is:
f
convert
f
convert
f
convert
f
convert
....
This continues until the stack overflows. It seems that the overloaded
cast operator has higher precedence than the contructor of B. I
appreciate this isn't the place to ask about specific C++ compilers, so
my question is: am I making unreasonable assumptions about what the
correct behaviour of C++ should be in these situations?
Thanks in advance,
Ross 3 2141
Ross wrote:
I have a problem regarding the precedence of overloaded cast
operators. My program is as follows:
#include <stdio.h>
class A;
class B {
public:
B(A &a) {
printf("constru ct\n");
}
};
class A {
public:
B f() {
printf("f\n");
return(B(*this) );
}
operator B () {
printf("convert \n");
return(f());
}
};
int main() {
A a;
a.f();
return(0);
}
When I compile and run the program on Linux using g++, the output is:
f
construct
This is pretty much what I'd expect. However, when I do the same on a
HP-UX system using aCC, the output is:
f
convert
f
convert
f
convert
f
convert
...
This continues until the stack overflows. It seems that the overloaded
cast operator has higher precedence than the contructor of B. I
appreciate this isn't the place to ask about specific C++ compilers,
so my question is: am I making unreasonable assumptions about what the
correct behaviour of C++ should be in these situations?
5.2.3 requires that the expression B(*this) is interpreted as a c-tor
invocation (construction of a value of type B). So, I think HP's aCC
is wrong.
V
--
Please remove capital 'A's when replying by e-mail
I do not respond to top-posted replies, please don't ask
Victor Bazarov:
5.2.3 requires that the expression B(*this) is interpreted as a c-tor
invocation (construction of a value of type B). So, I think HP's aCC
is wrong.
Are you saying the following?
When the following syntax is encountered:
A(obj_b)
, the compiler shall search for a constructor for A before it searches for
a conversion operator for B?
The following compiles OK for me with g++:
class A {};
class B {
public:
operator A() const
{
return A();
}
};
int main()
{
A obj_a;
B obj_b;
obj_a = obj_b;
obj_a = A(obj_b);
}
Even though the "function call syntax" or whatever you want to call it is
used, the conversion operator is still invoked. But are you saying that a
constructor must be sought before a conversion operator is sought?
--
Frederick Gotham
Frederick Gotham wrote:
Victor Bazarov:
>5.2.3 requires that the expression B(*this) is interpreted as a c-tor invocation (construction of a value of type B). So, I think HP's aCC is wrong.
Are you saying the following?
When the following syntax is encountered:
A(obj_b)
, the compiler shall search for a constructor for A before it
searches for a conversion operator for B?
The following compiles OK for me with g++:
class A {};
class B {
public:
operator A() const
{
return A();
}
};
int main()
{
A obj_a;
B obj_b;
obj_a = obj_b;
obj_a = A(obj_b);
}
Even though the "function call syntax" or whatever you want to call
it is used, the conversion operator is still invoked. But are you
saying that a constructor must be sought before a conversion operator
is sought?
Yes. However, in this case A(const A&) is the constructor invoked,
and the reference is the one bound to a temporary returned from the
conversion operator ('B::operator A()'). Try adding a parameterised
constructor to A and making it private.
class A { A(class B const&); public: A(); }; // I changed this
class B {
public:
operator A() const { return A(); }
};
int main()
{
A obj_a;
B obj_b;
obj_a = obj_b; // now it's ambiguous
obj_a = A(obj_b); // now it cannot access the c-tor
}
AFAICT, in the original variation both cases _can_ be made equivalent
by the compiler because it is allowed to eliminate extra temporaries.
V
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