CODEWITHSUNDEEP
c++debuggingloggingostreamfilebuf
RotsiserMho
RotsiserMho

Reputation: 31

Trying to derive from wfilebuf (filebuf) for logging

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!

Upvotes: 0

Views: 392

Answers (1)

Jerry Coffin
Jerry Coffin

Reputation: 490128

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.

Upvotes: 0

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