Hi,

Running the following code:

#include <memory>

using namespace std;
  
class CBase {};
class CDerived : public CBase {};

void Set(auto_ptr<CBase> base)
{
}

int main(int argc, char *argv[])
{
  auto_ptr<CDerived> derived(new CDerived);

  Set(derived); // error: conversion from 'std::auto_ptr<CDerived>' to 'std::auto_ptr<CBase>' is ambiguous

  auto_ptr<CBase> base(derived); // but this is OK
  base = derived; // this is OK too
}

the Set(derived) gives the mentioned error in the comment. The next two lines compiles without error so both the copy constructor and the operator= of auto_ptr works fine. But for some reason the conversion is ambiguous if a function (in this case Set) is called.

In the next two lines of the compiler output, there are two notes:
/usr/include/c++/4.2.1/memory:368: note: candidates are: std::auto_ptr<_Tp>::operator std::auto_ptr<_Tp1>() [with _Tp1 = CBase, _Tp = CDerived]
/usr/include/c++/4.2.1/memory:212: note: std::auto_ptr<_Tp>::auto_ptr(std::auto_ptr<_Tp1>&) [with _Tp1 = CDerived, _Tp = CBase]

Please could you check if this is a bug or I made something wrong?

Thanks,
Csaba