std::vector<std::ofstream>::erase is giving compile error

3
votes

Hi I'm trying to do some file operations and if needed user can open multiple files. I've created a vector derived ofstream but when I want to erase i. element (which file has closed) with std::vector<Type>::erase(std::vector<Type>::iterator) compiler is giving me error but I have another vector derived std::string and I'm erasing it same way it's not giving error. My codes are;

#include <iostream>
#include <fstream>
#include <vector>

std::vector<std::ofstream> of;
std::vector<std::string> sv;

int CloseFile(int id, file_t ft) {
    std::vector<std::ofstream>::iterator i;
    std::vector<std::string>::iterator j;
    if (of[id].is_open() == true) {
        of[id].close();
        i = of.begin() + id;
        j = sv.begin() + id;
        of.erase(i); // showing error for this line
        sv.erase(j);
    }
}

I'm using Nsight Eclipse Edition 6.0 on Ubuntu 12.04 and I need open file or files anyway the errors from Problem section of eclipse outputs are;

  1. required from ‘_OI std::__copy_move_a(_II, _II, _OI) [with bool _IsMove = false; _II = std::basic_ofstream; _OI = std::basic_ofstream]
  2. required from ‘_OI std::__copy_move_a2(_II, _II, _OI) [with bool _IsMove = false; _II = __gnu_cxx::__normal_iterator*, std::vector > >; _OI = __gnu_cxx::__normal_iterator*, std::vector > >]
  3. required from ‘_OI std::copy(_II, _II, _OI) [with _II = __gnu_cxx::__normal_iterator*, std::vector > >; _OI = __gnu_cxx::__normal_iterator*, std::vector > >]
  4. required from ‘_OI std::copy(_II, _II, _OI) [with _II = __gnu_cxx::__normal_iterator*, std::vector > >; _OI = __gnu_cxx::__normal_iterator*, std::vector > >]
  5. std::basic_streambuf<_CharT, _Traits>& std::basic_streambuf<_CharT, _Traits>::operator=(const std::basic_streambuf<_CharT, _Traits>&) [with _CharT = char; _Traits = std::char_traits]
  6. std::ios_base& std::ios_base::operator=(const std::ios_base&)
  7. make: *** [dosya/dosya.o] Error 1
  8. within this content
  9. within this content
  10. required from here

The last error which is indicating code line

Compiler output: (Some words are in Turkish, dosya = file, GeriDonus_t = Return_t, DosyaKapat = FileClose)

16:06:56 **** Incremental Build of configuration Debug for project deneme ****`
make all`
Building file: ../dosya/dosya.cpp`
Invoking: NVCC Compiler`
/usr/local/cuda-6.0/bin/nvcc -I"/usr/local/cuda-6.0/samples/3_Imaging" -I"/usr/local    /cuda-6.0/samples/common/inc" -I"/opt/Calismalar/Cuda/cuda-workspace/deneme" -I/usr/local/opencv/include -I/usr/local/opencv/include/opencv -I/opt/Calismalar/Cuda/cuda-workspace/deneme/ -G -g -O0 -gencode arch=compute_30,code=sm_30 -gencode arch=compute_32,code=sm_32  -odir "dosya" -M -o "dosya/dosya.d" "../dosya/dosya.cpp"`
nvcc warning : The 'compute_10' and 'sm_10' architectures are deprecated, and may be removed in a future release.`
/usr/local/cuda-6.0/bin/nvcc -I"/usr/local/cuda-6.0/samples/3_Imaging" -I"/usr/local/cuda-6.0/samples/common/inc" -I"/opt/Calismalar/Cuda/cuda-workspace/deneme" -I/usr/local/opencv/include -I/usr/local/opencv/include/opencv -I/opt/Calismalar/Cuda/cuda-workspace/deneme/ -G -g -O0 --compile  -x c++ -o  "dosya/dosya.o" "../dosya/dosya.cpp"
In file included from /usr/include/c++/4.8/ios:42:0,
                 from /usr/include/c++/4.8/ostream:38,
                 from /usr/include/c++/4.8/iostream:39,
                 from ../dosya/dosya.h:13,
                 from ../dosya/dosya.cpp:9:
/usr/include/c++/4.8/bits/basic_ios.h: In instantiation of ‘static _OI std::__copy_move<false, false, std::random_access_iterator_tag>::__copy_m(_II, _II, _OI) [with _II = std::basic_ofstream<char>*; _OI = std::basic_ofstream<char>*]’:
/usr/include/c++/4.8/bits/stl_algobase.h:390:70:   required from ‘_OI std::__copy_move_a(_II, _II, _OI) [with bool _IsMove = false; _II = std::basic_ofstream<char>*; _OI = std::basic_ofstream<char>*]’
/usr/include/c++/4.8/bits/stl_algobase.h:428:38:   required from ‘_OI std::__copy_move_a2(_II, _II, _OI) [with bool _IsMove = false; _II = __gnu_cxx::__normal_iterator<std::basic_ofstream<char>*, std::vector<std::basic_ofstream<char> > >; _OI = __gnu_cxx::__normal_iterator<std::basic_ofstream<char>*, std::vector<std::basic_ofstream<char> > >]’
/usr/include/c++/4.8/bits/stl_algobase.h:460:17:   required from ‘_OI std::copy(_II, _II, _OI) [with _II = __gnu_cxx::__normal_iterator<std::basic_ofstream<char>*, std::vector<std::basic_ofstream<char> > >; _OI = __gnu_cxx::__normal_iterator<std::basic_ofstream<char>*, std::vector<std::basic_ofstream<char> > >]’
/usr/include/c++/4.8/bits/vector.tcc:138:2:   required from ‘std::vector<_Tp, _Alloc>::iterator std::vector<_Tp, _Alloc>::erase(std::vector<_Tp, _Alloc>::iterator) [with _Tp = std::basic_ofstream<char>; _Alloc = std::allocator<std::basic_ofstream<char> >; std::vector<_Tp, _Alloc>::iterator = __gnu_cxx::__normal_iterator<std::basic_ofstream<char>*, std::vector<std::basic_ofstream<char> > >; typename std::_Vector_base<_Tp, _Alloc>::pointer = std::basic_ofstream<char>*]’
../dosya/dosya.cpp:152:27:   required from here
/usr/include/c++/4.8/bits/ios_base.h:789:5: error: ‘std::ios_base& std::ios_base::operator=(const std::ios_base&)’ is private
     operator=(const ios_base&);
     ^
In file included from /usr/include/c++/4.8/ios:44:0,
                 from /usr/include/c++/4.8/ostream:38,
                 from /usr/include/c++/4.8/iostream:39,
                 from ../dosya/dosya.h:13,
                 from ../dosya/dosya.cpp:9:
/usr/include/c++/4.8/bits/basic_ios.h:66:11: error: within this context
     class basic_ios : public ios_base
           ^
In file included from /usr/include/c++/4.8/iostream:39:0,
                 from ../dosya/dosya.h:13,
                 from ../dosya/dosya.cpp:9:
/usr/include/c++/4.8/ostream:58:11: note: synthesized method ‘std::basic_ios<char>& std::basic_ios<char>::operator=(const std::basic_ios<char>&)’ first required here 
     class basic_ostream : virtual public basic_ios<_CharT, _Traits>
           ^
In file included from ../dosya/dosya.h:14:0,
                 from ../dosya/dosya.cpp:9:
/usr/include/c++/4.8/fstream:599:11: note: synthesized method ‘std::basic_ostream<char>& std::basic_ostream<char>::operator=(const std::basic_ostream<char>&)’ first required here 
     class basic_ofstream : public basic_ostream<_CharT,_Traits>
           ^
In file included from /usr/include/c++/4.8/ios:43:0,
                 from /usr/include/c++/4.8/ostream:38,
                 from /usr/include/c++/4.8/iostream:39,
                 from ../dosya/dosya.h:13,
                 from ../dosya/dosya.cpp:9:
/usr/include/c++/4.8/streambuf:810:7: error: ‘std::basic_streambuf<_CharT, _Traits>& std::basic_streambuf<_CharT, _Traits>::operator=(const std::basic_streambuf<_CharT, _Traits>&) [with _CharT = char; _Traits = std::char_traits<char>]’ is private
       operator=(const basic_streambuf&) { return *this; };
       ^
In file included from ../dosya/dosya.h:14:0,
                 from ../dosya/dosya.cpp:9:
/usr/include/c++/4.8/fstream:72:11: error: within this context
     class basic_filebuf : public basic_streambuf<_CharT, _Traits>
           ^
/usr/include/c++/4.8/fstream:599:11: note: synthesized method ‘std::basic_filebuf<char>& >std::basic_filebuf<char>::operator=(const std::basic_filebuf<char>&)’ first required here 
     class basic_ofstream : public basic_ostream<_CharT,_Traits>
           ^
In file included from /usr/include/c++/4.8/bits/char_traits.h:39:0,
                 from /usr/include/c++/4.8/ios:40,
                 from /usr/include/c++/4.8/ostream:38,
                 from /usr/include/c++/4.8/iostream:39,
                 from ../dosya/dosya.h:13,
                 from ../dosya/dosya.cpp:9:
/usr/include/c++/4.8/bits/stl_algobase.h:335:18: note: synthesized method ‘std::basic_ofstream<char>& std::basic_ofstream<char>::operator=(const std::basic_ofstream<char>&)’ first required here 
        *__result = *__first;
                  ^
make: *** [dosya/dosya.o] Error 1

16:06:57 Build Finished (took 456ms)`

I have no idea for that. I've also looked this, this, this, this (it's about an eclipse bug), FAQ - q7.1, this (about List but error is same and say error actually not error and I didn't change the compiler (nvcc)). Thanks everyone.

3
c++c++11stdvectorofstreamnsight
std::ofstreams can't be copied. You need to use pointers. – molbdnilo
@molbdnilo thank you – Orkun Kasapoglu
Why std::vector is using operator= for add or delete? Isn't it have done with pointer queue or stack and use free(void*) after delete an element? Is it about c++11 standard definitions? – Orkun Kasapoglu
I've changed the vector definition to std::vector<std::ofstream*> of; and now there is no error but I didn't try it yet. Thanks everyone again. – Orkun Kasapoglu
Suggestion vector<unique_ptr<ostream>> – Neil Kirk

3 Answers

2
votes

Gcc-4.8 does not support moving streams. Your code is conforming to C++11 in this regard, just your implementation is not.

1
votes

A std::vector holds its elements in a continuous block of memory without gaps. To erase an element causes all elements behind to be moved or copied to new positions. The std::ofstream in this case cant be moved, so it runs in an compiling error.

Dont use std::ofstream directly in a std::vector. It works with references, pointers or - i prefere - std::unique_ptr.

It also works with std::list instead of vector. std::list has an other way of holding its elements, it dont move them. But i am not sure if that is a better way than reference/pinter/std_unique_ptr in a std:vector.

-2
votes

I've changed code and it has no error now. Thanks to everyone.

Now it is:

#include <iostream>
#include <fstream>
#include <string>
#include <stdlib.h>

std::vector<std::ofstream*> of;
std::vector<std::string> sv;

int CloseFile(int id, file_t ft) {
    std::vector<std::ofstream*>::iterator i;
    std::vector<std::string>::iterator j;
    if (of[id]->is_open() == true) {
        of[id]->close();
        i = of.begin() + id;
        j = sv.begin() + id;
        free(of[id]);
        of.erase(i);
        sv.erase(j);
    }
}

but i didn't try it yet. Just there is no compiler error now.