Having trouble accessing members of a struct

**Swarvy** · 10-02-2009

I want to have multiple file instances open at a given time (probably only 5-10 at time at most). So one way I thought of doing it was to have a structure with the fstream instance and the filename (and any other information). Although, when I try and access the structure to set the contents, it gives me the error message: "m_fileio has not been declared". I haven't programmed in a while, so I'm a little out of touch. The error is quite self-explanatory, I'm just not sure why it says they aren't defined.

Structure Definition:

Code:

struct FILE_STRUCT
{
       std::fstream m_fileio;
       std::string m_filename;
};

Code for setting the members of the struct (p_file is a vector of FILE_STRUCT pointers):

Code:

p_file.push_back( new FILE_STRUCT );
     
( (p_file.end() )->m_fileio).open(filename.c_str());
( p_file.end() )->m_filename = filename;

**tabstop** · 10-02-2009

This seems all weird here, since .end() has never and will never return anything valid to use. But the usual: small, compilable example that shows the difficulty, please.

**anon** · 10-02-2009

If you want to refer to the last item in a container, use the back() method

**Swarvy** · 10-03-2009

Thanks guys, it turns out the only problem was that I was using the 'end()' method instead of 'back()'. Although since then, a further problem has arised with trying to make a 'CloseAllFiles' function. Here is the code and the corresponding error message I get when I try and compile.

Code:

void FILEIO::CloseAllFiles()
{
     int idx;
     
     for(idx = p_file.size(); idx >= 0; idx--)
     {
                ( p_file[ p_file.begin() + idx ]->m_fileio).close();
                delete p_file[ p_file.begin() + idx ];
     }
     
     p_file.clear();
}

Error Message:

Code:

132 C:\Dev-Cpp\Programs\Development Projects\BOF\fileio.cpp no match for 'operator[]' in
  '((FILEIO*)this)->FILEIO::p_file[(&(((std::vector<FILE_STRUCT*, std::allocator<FILE_STRUCT*> >*)((FILEIO*)this)) + 4u)->
    std::vector<_Tp, _Alloc>::begin [with _Tp = FILE_STRUCT*, _Alloc = std::allocator<FILE_STRUCT*>]())->
    __gnu_cxx::__normal_iterator<_Iterator, _Container>::operator+ 
  [with
    _Iterator = FILE_STRUCT**,
    _Container = std::vector<FILE_STRUCT*, std::allocator<FILE_STRUCT*> >
  ](((const ptrdiff_t&)((const ptrdiff_t*)(&idx))))]'

It says from the error message that the use of '[]' is the problem. I'm not entirely sure why though.

**CornedBee** · 10-03-2009

You're trying to index the vector with an iterator. That's wrong. You can indext with an index (p_file[idx]) or dereference an iterator (*(p_file.begin() + idx)).

**anon** · 10-03-2009

The error message is too long to read.

However:

Code:

p_file[ p_file.begin() + idx ]

should be exactly the same as

Code:

p_file[idx];

It also seems to me, that again you are trying to access the one-beyond-the-last item (p_file[p_file.size()] is out of range).

You're trying to index the vector with an iterator.

Doh.

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