custom ostream for debugPrint purposes

[lars]

Hi,

I have C (printf) style debug functions

static void debugPrint(Silver::Strategy& s, unsigned level, const char
*format, ...)
{
if (s.verbosityLevel() >= level ) {
va_list args ;
va_start(args, format);
vfprintf(stdout, format, args);
}
}

debugPrint(s,1,"blabla\n");

Now I want the same facility, but using ostreams. I want to be able to
write

debugPrint(s,1) << "blabla" << std::endl;

static ostream& debugPrint(Silver::Strategy& s, unsigned level)
{
if (s.verbosityLevel() >= level ) return std::cout;

// Whats next?
return ??

How can I create a black-hole / void ostream object?

Any help I can get is greatly appreciated.
Cheers,
-L

[Stuart Redmann]

lars wrote:

Hi,

I have C (printf) style debug functions

static void debugPrint(Silver::Strategy& s, unsigned level, const char
*format, ...)
{
if (s.verbosityLevel() >= level ) {
va_list args ;
va_start(args, format);
vfprintf(stdout, format, args);
}
}

debugPrint(s,1,"blabla\n");

Now I want the same facility, but using ostreams. I want to be able to
write

debugPrint(s,1) << "blabla" << std::endl;

static ostream& debugPrint(Silver::Strategy& s, unsigned level)
{
if (s.verbosityLevel() >= level ) return std::cout;

// Whats next?
return ??

How can I create a black-hole / void ostream object?

Simply create one for yourself:

include <iostream>
#include <ostream>
#include <iomanip>
#include "stdarg.h"

// I couldn't figure out how to call the constructor of ostream
// without this using this namespace.
using namespace std;
static void debugPrint(unsigned level, const char *format, ...)
{
va_list args ;
va_start (args, format);
vfprintf (stdout, format, args);
}

class CBlackHoleStream : public ostream
{
public:
CBlackHoleStream ()
: ostream (NULL, false, false) {}
};

static CBlackHoleStream g_BlackHoleStream;

static ostream& debugPrint(unsigned level)
{
if (level 0)
return std::cout;

// Whats next?
return g_BlackHoleStream;
}

int main ()
{
debugPrint (0) << "Test\n" << "Test2\n";
debugPrint (1) << "blabla\n";

return 0;
}

Regards,
Stuart

[VJ]

Stuart Redmann wrote:

>
// I couldn't figure out how to call the constructor of ostream
// without this using this namespace.
using namespace std;
static void debugPrint(unsigned level, const char *format, ...)
{
va_list args ;
va_start (args, format);
vfprintf (stdout, format, args);
}

class CBlackHoleStream : public ostream

class CBlackHoleStream : public std::ostream

{
public:
CBlackHoleStream ()
: ostream (NULL, false, false) {}

: std::ostream (NULL, false, false) {}

};

static CBlackHoleStream g_BlackHoleStream;

static ostream& debugPrint(unsigned level)

static std::ostream& debugPrint(unsigned level)

{
if (level 0)
return std::cout;

// Whats next?
return g_BlackHoleStream;
}

int main ()
{
debugPrint (0) << "Test\n" << "Test2\n";
debugPrint (1) << "blabla\n";

return 0;
}

Tried these things?

[Roland Pibinger]

On 27 Oct 2006 03:05:41 -0700, "lars" <la**@jasper-da.comwrote:

>I have C (printf) style debug functions

static void debugPrint(Silver::Strategy& s, unsigned level, const char
*format, ...)
{
if (s.verbosityLevel() >= level ) {
va_list args ;
va_start(args, format);
vfprintf(stdout, format, args);
}
}

debugPrint(s,1,"blabla\n");

This is not optimal because your arguments are always evaluated, even
when nothing is printed.

>Now I want the same facility, but using ostreams. I want to be able to
write

debugPrint(s,1) << "blabla" << std::endl;

static ostream& debugPrint(Silver::Strategy& s, unsigned level)
{
if (s.verbosityLevel() >= level ) return std::cout;

// Whats next?
return ??

How can I create a black-hole / void ostream object?

You can but you also suffer from unnecessary evaluations (more a
problem in C++ than in C). C++ log libraries with ostream interface
usually have ugly looking macros to avoid that. The following sketch
of a solution uses templates instead of macros:

#ifndef LOGGER_H
#define LOGGER_H

#include <ostream>

template <typename T1>
bool log (std::ostream& os, const T1& t1) {
os << t1 << std::endl;
return true;
}

template <typename T1, typename T2>
bool log (std::ostream& os, const T1& t1, const T2& t2) {
os << t1 << " " << t2 << std::endl;
return true;
}

template <typename T1, typename T2, typename T3>
bool log (std::ostream& os, const T1& t1, const T2& t2, const T3& t3)
{
os << t1 << " " << t2 << " " << t3 << std::endl;
return true;
}

// and so on ...

enum LogLevel {
eTrace = 1, eError
};
class LogStrategy {
public:
LogStrategy(): level (0) {}

bool trace() { return level <= eTrace; }
bool error() { return level <= eError; }
void setLevel (LogLevel ll) { level = ll; }
private:
int level;
LogStrategy (const LogStrategy&);
LogStrategy& operator= (const LogStrategy&);
};

#endif // LOGGER_H
A test file:

#include <iostream>
#include "Logger.h"

using namespace std;

int main (int argc, char* argv[])
{
LogStrategy s;
s.setLevel (eTrace);
// s.setLevel (eError);

s.trace() && log (cout, "Hello, world!");
s.trace() && log (cout, "result", 3.14159265);
s.error() && log (cout, 123.456, "something wrong", 789);
}

Best wishes,
Roland Pibinger

[lars]

: std::ostream (NULL, false, false) {}

error: no matching function for call to `std::basic_ostream<char,
std::char_traits<char::basic_ostream(const void**, NULL, bool, bool)

What is this constructor you are using? Is it standard? How do I get it
in scope?

Cheers,
-L

VJ wrote:

Stuart Redmann wrote:

// I couldn't figure out how to call the constructor of ostream
// without this using this namespace.
using namespace std;
static void debugPrint(unsigned level, const char *format, ...)
{
va_list args ;
va_start (args, format);
vfprintf (stdout, format, args);
}

class CBlackHoleStream : public ostream

class CBlackHoleStream : public std::ostream

{
public:
CBlackHoleStream ()
: ostream (NULL, false, false) {}

: std::ostream (NULL, false, false) {}

};

static CBlackHoleStream g_BlackHoleStream;

static ostream& debugPrint(unsigned level)

static std::ostream& debugPrint(unsigned level)

{
if (level 0)
return std::cout;

// Whats next?
return g_BlackHoleStream;
}

int main ()
{
debugPrint (0) << "Test\n" << "Test2\n";
debugPrint (1) << "blabla\n";

return 0;
}

Tried these things?

[VJ]

lars wrote:

>>: std::ostream (NULL, false, false) {}

error: no matching function for call to `std::basic_ostream<char,
std::char_traits<char::basic_ostream(const void**, NULL, bool, bool)

What is this constructor you are using? Is it standard? How do I get it
in scope?

Cheers,
-L

VJ wrote:

>>Stuart Redmann wrote:

>>>// I couldn't figure out how to call the constructor of ostream
// without this using this namespace.
using namespace std;
static void debugPrint(unsigned level, const char *format, ...)
{
va_list args ;
va_start (args, format);
vfprintf (stdout, format, args);
}

class CBlackHoleStream : public ostream

class CBlackHoleStream : public std::ostream

>>>{
public:
CBlackHoleStream ()
: ostream (NULL, false, false) {}

: std::ostream (NULL, false, false) {}

>>>};

static CBlackHoleStream g_BlackHoleStream;

static ostream& debugPrint(unsigned level)

static std::ostream& debugPrint(unsigned level)

>>>{
if (level 0)
return std::cout;

// Whats next?
return g_BlackHoleStream;
}

int main ()
{
debugPrint (0) << "Test\n" << "Test2\n";
debugPrint (1) << "blabla\n";

return 0;
}

Tried these things?

ok, i wanted to do it fast, but here is copy/paste of the code that
works on my computer (linux / g++)

#include <iostream>
#include <iomanip>

#include "stdarg.h"

static void debugPrint(unsigned level, const char *format, ...)
{
va_list args ;
va_start (args, format);
vfprintf (stdout, format, args);
}

class CBlackHoleStream : public std::ostream
{
public:
CBlackHoleStream ()
: std::ostream (NULL) {}
};

static CBlackHoleStream g_BlackHoleStream;

static std::ostream& debugPrint(unsigned level)
{
if (level 0)
return std::cout;

// Whats next?
return g_BlackHoleStream;
}

int main ()
{
debugPrint (0) << "Test\n" << "Test2\n"<<std::endl;
debugPrint (1) << "blabla\n"<<std::endl;

return 0;
}