Having lots of problems understand how exactly to use the iostream classes. I have a class, which does alot of reading of individual characters. I wanted to make this an abstract enough so that i could be reading from a location in memory... from a file..... etc. In my class, i have a member variable defined as such: std::istream m_Stream; however, in my Constructor for the class, i keep getting the following error: ''std::basic_istream<_Elem,_Traits>'' no appropriate default constructor available I''m using VC++ 7.0 (the .net one) ... and looking at the definition of istream ... is just a specialized basic_istream for char''s ... and there is no default constructor for basic_istream theres a constructor for taking a streambuf, and one that takes a std::_Uninitialized enumeration. MS''s documentation is very sketchy and i can''t seem to find much about using iostreams. When searching online, most every site i find says the istream SHOULD have a default constructor. Also... in VC++ 7.0 ... ifstream is NOT derived from istream ... ifstream is a specialization of basic_ifstream for char''s ... and basic_ifstream is derived from basic_istream. Should i be using basic_istream for my class member instead then?? ... so i could pass a ifstream or an istream object?? Are these classes all messed up from standard?? or am i just trying to use them wrong??

Ok, found some documentation on MSDN, they dont list a default constructor for istream, but GNU C++'s version does. So i guess i can't use istream like i thought. I need my client to pass me a streambuf instead of an istream class. So i guess the real question now is, can i construct my istream member, with a NULL pointer and then change it later? Also, does the istream class destroy the streambuf when its destroyed?

Also, MSDN documentation that i found does say ifstream is suppose to be derived from istream, but just a simple program below generates an error.

int main()
{
ifstream mystream;
(istream)mystream;
}

error C2440: 'type cast' : cannot convert from 'std::ifstream' to 'std::istream'.

I take it, this is just an an incompatibility with MS's implemtnation of the STL classes or im missing something here?


[edited by - Merick on June 27, 2002 12:42:32 PM]

im using VC++ 7.0, there are no current service packs for that. I'm thinking its a bug in the new .net libraries, but not sure. I've made a similar post on the MSDN's forums for VC++/STL, hoping to find out if this is a bug or intended change.

[edited by - Merick on June 27, 2002 1:49:53 PM]

Yep, if i typecast a pointer it works fine, but why is this?? If i used any other class it works. Like:

class A
{
public:
};

class B : public A
{
public:
};

int main()
{
B myB;
(A)myB;
}

compiles just fine for me. Whats different about istream and ifstream that prevents this same conversion?

EDIT:
would it be better to pass a pointer to an istream class in my constructor? or a pointer to a streambuf?? i'm not quite sure i understand how streambuf and istream work together to understand what would be the advantage of doing something one way or the other.

[edited by - Merick on June 27, 2002 2:31:09 PM]

hehe nm, got that question answered on the MSDN. Apparently, MSVC 6.0 allowed accidently had a copy constructor for the istream class, which is what allows the (istream)s statement to compile. They removed it in 7.0, which is why i got the error

well, this is for a lexical analyzer for a compiler im writting, so i can compile material settings, rendering states, scene graphs.... etc from a text file. I want it to flexiable enough that i might even be able to use it to parse user input from a console, script commands in memory. Its pretty similar to your output example, only with input And from what you said, i think istream * would be sufficent .... thanks ... hehe.. now if i can only figure out a way to define my lexical analyzer states without having to create 100 state classes or a 100 table entries.... i''ll be set