QUESTION:
In practice, lines 36 and 37 below are usually equivalent to the
default copy constructor (.e.g line 33). My questions are:
(a) Does ISO 14882 guarantee that lines 36 and 37 are equivalent
to executing the default copy constructor (i.e. lines 33)?
(b) If not, is the behavior for lines 36-39 well defined by the
standard?
While all C++ compilers I know of implement virtual functions by
storing a pointer to a vtable in the object the standard doesn't talk
about implementation details like this ...
Regards,
--jfc
1 #include <iostream>
2 #include <cstdlib>
3
4 class foo {
5 public:
6 int i;
7 foo(): i(3) {}
8 virtual void f() { std::cout << "foo" << std::endl; }
9 virtual ~foo() {};
10 };
11
12 class bish : public foo {
13 public:
14 int j;
15 double d;
16
17 bish(int p): j(p), d(0.0) {}
18 void f() { std::cout << "bish" << std::endl; }
19 ~bish() {};
20 };
21
22 int
23 main(int argc,char *argv[])
24 {
25 char buf1[sizeof(bish)];
26
27 bish b1(99);
28
29 // consttruct with placement new.
30 bish * b2 = new((void *)buf1) bish(42);
31
32 // copying with the default copy ctor
33 bish b3(b1);
34
35 // equivalent to copy construction?
36 bish * b4 = (bish *) new char[sizeof(bish)];
37 memcpy((char *)b4, (char *)&b1, sizeof(bish));
38
39 b4->f();
40 }
41
[ See http://www.gotw.ca/resources/clcm.htm for info about ]
[ comp.lang.c++.m oderated. First time posters: Do this! ]
In practice, lines 36 and 37 below are usually equivalent to the
default copy constructor (.e.g line 33). My questions are:
(a) Does ISO 14882 guarantee that lines 36 and 37 are equivalent
to executing the default copy constructor (i.e. lines 33)?
(b) If not, is the behavior for lines 36-39 well defined by the
standard?
While all C++ compilers I know of implement virtual functions by
storing a pointer to a vtable in the object the standard doesn't talk
about implementation details like this ...
Regards,
--jfc
1 #include <iostream>
2 #include <cstdlib>
3
4 class foo {
5 public:
6 int i;
7 foo(): i(3) {}
8 virtual void f() { std::cout << "foo" << std::endl; }
9 virtual ~foo() {};
10 };
11
12 class bish : public foo {
13 public:
14 int j;
15 double d;
16
17 bish(int p): j(p), d(0.0) {}
18 void f() { std::cout << "bish" << std::endl; }
19 ~bish() {};
20 };
21
22 int
23 main(int argc,char *argv[])
24 {
25 char buf1[sizeof(bish)];
26
27 bish b1(99);
28
29 // consttruct with placement new.
30 bish * b2 = new((void *)buf1) bish(42);
31
32 // copying with the default copy ctor
33 bish b3(b1);
34
35 // equivalent to copy construction?
36 bish * b4 = (bish *) new char[sizeof(bish)];
37 memcpy((char *)b4, (char *)&b1, sizeof(bish));
38
39 b4->f();
40 }
41
[ See http://www.gotw.ca/resources/clcm.htm for info about ]
[ comp.lang.c++.m oderated. First time posters: Do this! ]
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