C++ application crashes while instantiating an ofstream object.

Question

I have a very irritating issue while running a C++ application. I am using the pgcpp compiler on the Interix subsystem of Windows Xp. My problem is essentially described here:

I have a class definition in a header file. This header file is included in one source file. This class has two constructors and is basically used to implement a logger. The first constructor takes ostream *out as an argument, while the second overloaded constructor takes a filename and a default boolean value of false. The objective of this second constructor is to get a stream for the filename that we are passing and to start logging messages to it. The code in the constructors is as follows:

MessageLogger::MessageLogger(std::ostream *out): p_out (out), p_ofstream (0)  
{  
    if (p_out)  
    {  
        (*p_out) << "Started logging messages" << endl;  
    }  
}  

MessageLogger::MessageLogger (char const *filename, bool append_to_file) : p_out (0),   p_ofstream (0)  
{  
    if (append_to_file)  
    {  
    p_ofstream = new std::ofstream (filename, ios::app);  
    }  
    else  
    {  
        p_ofstream = new std::ofstream (filename);  
    }  

    p_out = p_ofstream;  

    if (p_out)  
    {  
        (*p_out) << "Started logging messages" << endl;  
    }  
}  

Where the declarations of p_out and p_ofstream are as follows:

std::ostream *p_out;
std::ofstream *p_ofstream;
unsigned int p_indent_level;

All the three mentioned above are private members. The instantiation of the MessageLogger class is done as:

MessageLogger logger ("filename");

Please note that append_to_file has a default value of false. PGDBG is also misbehaving. I am inexplicably able to step in when the control is at p_ofstream = new std::ofstream (filename); and it steps into a random location and then the application crashes.

Also, when I try to see either of Mixed or Disassembly code in PGDBG, the debugger crashes with the message:

jpgdbg parse: Newline must follow cmd in 'eleq "0" struct MessageLogger *Mes
sageLogger::MessageLogger(struct basic_ostream *out); (TranslatorGeneric.cpp
)
'
jpgdbg jpgdbgFileSelector processMsg: Warning unexpected msg token 5
jpgdbg parse: Newline must follow cmd in 'eleq "1" struct MessageLogger *Mes
sageLogger::MessageLogger(char *filename, unsigned char append_to_file); (Tr
anslatorGeneric.cpp)
'
jpgdbg jpgdbgFileSelector processMsg: Warning unexpected msg token 5

I am unable to reproduce this in a sample program where I did the exact same thing as above but everything works fine. Can someone please explain what is happening and if there is a fix to this?

Thanks, Aditya.

Answer 1

Why are you using a dynamically allocated instance of ofstream? Why don't you do something like the following...

class Logger
{
  public:
    Logger(ostream& str) : _str(str.rdbuf()) // use the buffer from the stream
    {
      _str << "writing to passed in buffer" << endl;
    }
    Logger(const char* fname, bool append = false) : _str(cout.rdbuf())
    {
      _file.open(fname, (append)? ios::out|ios::app : ios::out);
      if (_file.is_open())
        _str.rdbuf(&_file); // redirects to file, else remains on cout

      _str << "expected to be logging to: " << fname << endl;
    }

    // use as needed

  private:
    filebuf _file;
    ostream _str;
};

This way even if your file fails, you'll still have the log output going to cout...

Back to your problem, what does HW_NEW do? It's kind of hard to say really with the basic information you've provided...