Trying to derive from wfilebuf (filebuf) for logging - c++

Question

I'm basically trying to derive from wfilebuf so I can both output to a file and intercept the output to print it to the console/debug window as well as illustrated here:
http://savingyoutime.wordpress.com/2009/04/21/ and/or here: http://savingyoutime.wordpress.com/2009/04/22/40/
(ancient supporting ideas here: http://www.horstmann.com/cpp/streams.txt)
I've almost got it, but I can't seem to be able to both write to the underlying file AND peek at the input.
I overrode the sync() function similar to the second example but it seems that pbase() and pptr() are always NULL unless I set a buffer with setp(...), but this seems to break the file output. The file is always empty!
My crude attempt at this is below:
class LoggerBuffer : public wfilebuf {
// Functions
public:
LoggerBuffer();
~LoggerBuffer();
void open(const wchar_t loggerFile[]);
void close();
int sync();
int_type overflow(int_type c = EOF);
void setState(int newState);
// Variables
private:
int currentState;
static const int BUFFER_SIZE = 10;
wchar_t buffer[BUFFER_SIZE];
};
class LoggerStream : public wostream {
// Functions
public:
LoggerStream();
~LoggerStream();
void open(const wchar_t loggerFile[] = 0);
void close();
void setState(int newState);
};
LoggerBuffer::LoggerBuffer() {
wfilebuf::open("NUL", wios::out); currentState = 1;
}
LoggerBuffer::~LoggerBuffer() {
wcout << "Destruction of LoggerBuffer" << endl;
}
void LoggerBuffer::open(const wchar_t loggerFile[]) {
wcout << "LoggerBuffer Opening " << loggerFile << endl;
close();
wfilebuf* temp = wfilebuf::open(loggerFile, wios::out); //ios::out | ios::app | ios::trunc
setp (buffer, buffer+(BUFFER_SIZE-1));
}
void LoggerBuffer::close() {
wfilebuf::close();
}
int LoggerBuffer::sync() {
wcout << " Syncing ";
int out_waiting = pptr() - pbase();
wcout << out_waiting << " characters!";
wcout << endl;
wcout << "pptr(): " << (unsigned int)pptr() << endl;
return wfilebuf::sync();
}
LoggerBuffer::int_type LoggerBuffer::overflow(int_type c) {
wcout << "overflow! (" << (wchar_t)c << ")" << endl;
if (c == EOF)
return EOF;
if (sync() == EOF)
return EOF;
return wfilebuf::overflow(c);
}
void LoggerBuffer::setState(int newState) {
wcout << "New buffer state = " << newState << endl;
currentState = newState;
}
LoggerStream::LoggerStream() : wostream(new LoggerBuffer), wios(0) {
}
LoggerStream::~LoggerStream() {
delete rdbuf();
}
void LoggerStream::open(const wchar_t loggerFile[]) {
wcout << "LoggerStream Opening " << loggerFile << endl;
((LoggerBuffer*)rdbuf())->open(loggerFile);
}
void LoggerStream::close() {
((LoggerBuffer*)rdbuf())->close();
}
void LoggerStream::setState(int newState) {
wcout << "New stream state = " << newState << endl;
((LoggerBuffer*)rdbuf())->setState(newState);
}
Full disclosure: I asked a question regarding something similar earlier: Simple wostream logging class (with custom stream manipulators)
I think I have solved that problem though.
Any help is greatly appreciated! Thanks!

Answer 1

I'd use a filtering streambuf, that does no buffering of its own, instead passing data through to a real streambuf (i.e., one that does real buffering) for each of the destinations. This should simplify your code quite a bit and let you concentrate on the parts you really care about.