The end of my streambuf road...

[Christopher Benson-Manica]

Unless there is something wrong with the following complete C++ file,
I think my quest to stream-ize our code will be at an end :(

#include <sstream>
#include <iostream>

using namespace std;

class linebuf : public streambuf
{
protected:
string buffer;

public:
virtual char overflow(char c) {if(c!=EOF) buffer+=c; return c;}
virtual streamsize xsputn(const char *s, streamsize num)
{
buffer.append(s,num); return num;
}
virtual int sync()=0;
};

typedef unsigned int uint;
typedef bool (* FTYPE)(const void *,uint,uint,uint);

class sendbuf : public linebuf
{
public:
virtual int sync() {cout << buffer << endl; buffer.erase(); return 0;}
};

class mystream : public std::ostream
{
protected:
sendbuf buf;

public:
mystream() : std::ostream(&buf) {}
};

int main(void)
{
mystream s;

s << "Hello, " << "world!" << flush;
return 0;
}

g++, faithful and true companion that it is, compiles and runs this as
expected with all warnings enabled. Our Borland setup, however,
compiles this into an executable that crashes. So I figure either I'm
invoking some wicked implementation-defined (or undefined!) behavior
here, or our Borland setup is fatally flawed in ways that I cannot
begin to fathom. Thanks to everyone who provided assistance during my
travails - it was a great learning experience if nothing else!

--
Christopher Benson-Manica | I *should* know what I'm talking about - if I
ataru(at)cyberspace.org | don't, I need to know. Flames welcome.

[Leor Zolman]

On Fri, 27 Feb 2004 18:40:03 +0000 (UTC), Christopher Benson-Manica
<at***@nospam.cyberspace.org> wrote:

Unless there is something wrong with the following complete C++ file,
I think my quest to stream-ize our code will be at an end :(

#include <sstream>
#include <iostream>

using namespace std;

class linebuf : public streambuf
{
protected:
string buffer;

public:
virtual char overflow(char c) {if(c!=EOF) buffer+=c; return c;}
virtual streamsize xsputn(const char *s, streamsize num)
{
buffer.append(s,num); return num;
}
virtual int sync()=0;
};

typedef unsigned int uint;
typedef bool (* FTYPE)(const void *,uint,uint,uint);

class sendbuf : public linebuf
{
public:
virtual int sync() {cout << buffer << endl; buffer.erase(); return 0;}
};

class mystream : public std::ostream
{
protected:
sendbuf buf;

public:
mystream() : std::ostream(&buf) {}
};

int main(void)
{
mystream s;

s << "Hello, " << "world!" << flush;
return 0;
}

g++, faithful and true companion that it is, compiles and runs this as
expected with all warnings enabled. Our Borland setup, however,
compiles this into an executable that crashes. So I figure either I'm
invoking some wicked implementation-defined (or undefined!) behavior
here, or our Borland setup is fatally flawed in ways that I cannot
begin to fathom. Thanks to everyone who provided assistance during my
travails - it was a great learning experience if nothing else!

Here's what Comeau says:
stream.cpp(13): warning: function "basic_streambuf<char,
char_traits<char>>::overflow(
basic_streambuf<char, char_traits<char>>::int_type)" is hidden by
"linebuf::overflow" --
virtual function override intended?
virtual char overflow(char c) {if(c!=EOF) buffer+=c; return
c;}
^

(the caret is pointing at the start of the word "overflowa" in the last
line). Any help?
-leor
Leor Zolman
BD Software
le**@bdsoft.com
www.bdsoft.com -- On-Site Training in C/C++, Java, Perl & Unix
C++ users: Download BD Software's free STL Error Message
Decryptor at www.bdsoft.com/tools/stlfilt.html

[Christopher Benson-Manica]

Leor Zolman <le**@bdsoft.com> spoke thus:

stream.cpp(13): warning: function "basic_streambuf<char,
char_traits<char>>::overflow(
basic_streambuf<char, char_traits<char>>::int_type)" is hidden by
"linebuf::overflow" --
virtual function override intended?
virtual char overflow(char c) {if(c!=EOF) buffer+=c; return
c;}
^ (the caret is pointing at the start of the word "overflowa" in the last
line). Any help?

It is int_type in the code compiled by Borland - I changed it because
g++ complained...

--
Christopher Benson-Manica | I *should* know what I'm talking about - if I
ataru(at)cyberspace.org | don't, I need to know. Flames welcome.

[Dietmar Kuehl]

Christopher Benson-Manica wrote:

class linebuf : public streambuf
{
protected:
string buffer;
There is no point in making member variables protected: you could as
well make them public they become part of your interface anyway (well,
given that the size changes with a type change, in some sense even
private variables are part of the interface...). However, this is not
really your problem...
public:
virtual char overflow(char c) {if(c!=EOF) buffer+=c; return c;}

This is not an override but an overload! You should use 'int_type'
or, if this causes problems, 'std::char_traits<char>::int_type'.
Using 'char' will definitely cause problems. The 'overflow()'
function would look something like this:

int_type overflow(int_type c) {
if (!traits::eq_int_type(c, traits::eof()))
buffer += traits::to_char_type(c);
return traits::not_eof(c);
}
--
<mailto:di***********@yahoo.com> <http://www.dietmar-kuehl.de/>
Phaidros eaSE - Easy Software Engineering: <http://www.phaidros.com/>