Problem with ostringstream and copy constructor

Question

Possible Duplicates:
Why copying stringstream is not allowed?
how copy from one stringstream object to another in C++?

Compiling class T fails with Visual C++ and GCC producing iostreams template errors. Here is the code:

#include <sstream>

class T
{
  static T copy;

  std::ostringstream log;

  T()            {}
  T(const T& t)  {log  = t.log;}
  ~T()           {copy = *this;}
};

T T::copy;

Changing log data member type to string makes it compile and run OK. Is this a legitimate behavior?

Nawaz · Accepted Answer · 2011-08-13T10:17:40.687

4

Copy constructor and copy-assignment of any stream class in C++ has been made private. That means, you cannot make copy of std::ostringstream object:

std::ostringstream ss;

std::ostringstream ss1(ss); //not allowed - copy-constructor is private
ss1=ss; //not allowed - copy-assignment is private

edited Aug 13 '11 at 10:17

answered Aug 13 '11 at 10:06

Nawaz

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OK, that's true, but I'm getting the same error even with empty copy-constructor: `T(const T& t) {}` – Paul Jurczak Aug 13 '11 at 10:49
@Paul: Post the actual code, and the error. – Nawaz Aug 13 '11 at 10:55
@Nawasz: Code is as in my question above with copy-constructor replaced with: `T(const T& t) {}` or `T(const T& t) {log << t.log.str();}` or `T(const T& t) {log << t.log.rdbuf();}`. I'm always getting: _'std::basic_ios<_Elem,_Traits>::operator =' : no accessible path to private member declared in virtual base 'std::basic_ios<_Elem,_Traits>'_ – Paul Jurczak Aug 13 '11 at 11:06
@Paul: Alright. That is because of this line `copy = *this;` which invokes `operator=() generated by the compiler; the generated code has this line `copy.log= (*this).log` which is causing problem. That means, if you comment the line `copy=*this;` then it will compile fine. Atleast that error will not show up. – Nawaz Aug 13 '11 at 11:13
Thank you. I fell into copy constructor vs. assignment operator trap. – Paul Jurczak Aug 13 '11 at 11:29
@Paul: Its not `copy constructor vs. assignment operator trap`. Its *copy constructor **and** assignment operator trap* which I said in the very beginning of my answer. – Nawaz Aug 13 '11 at 11:32

score 3 · Answer 2 · edited May 23 '17 at 10:34

3

std::ostringstream is not copyable that's why you are getting error. See this answer for more details to know how you can overcome this problem.

T(const T& t)  {log << t.log.rdbuf(); }

edited May 23 '17 at 10:34

Community

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answered Aug 13 '11 at 10:06

iammilind

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It still produces the same error: 'std::basic_ios<_Elem,_Traits>::operator =' : no accessible path to private member declared in virtual base 'std::basic_ios<_Elem,_Traits>' – Paul Jurczak Aug 13 '11 at 10:39

score 1 · Answer 3 · answered Aug 13 '11 at 10:05

1

I think ostringstream has no overloaded assignment(=) operator.

answered Aug 13 '11 at 10:05

MetallicPriest

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Problem with ostringstream and copy constructor

3 Answers3

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