debug.h File Reference

RE/flex debug logs. More...

This graph shows which files directly or indirectly include this file:

Macros
#define	DBGLOG(...)   (void)0
	When compiled with -DDEBUG, adds a timestamped log entry with a printf-formatted message. More...
#define	DBGLOGN(...)   (void)0
	When compiled with -DDEBUG, adds a log entry with a printf-formatted message. More...
#define	DBGLOGA(...)   (void)0
	When compiled with -DDEBUG, appends a printf-formatted message to the last log entry. More...

Detailed Description

RE/flex debug logs.

Author

Robert van Engelen - engel.nosp@m.en@g.nosp@m.enivi.nosp@m.a.co.nosp@m.m

Copyright

(c) 2015-2016, Robert van Engelen, Genivia Inc. All rights reserved.

(c) BSD-3 License - see LICENSE.txt

Exploiting macro magic to simplify debug logging.

Usage

DBGLOG(format, ...) creates a timestamped log entry with a printf-formatted message. The log entry is added to a log file or sent to stderr as specified:

Source files compiled with	DBGLOG(...) entry added to
c++ -DDEBUG	DEBUG.log
c++ -DDEBUG=TEST	TEST.log
c++ -DDEBUG=	stderr

DBGLOGN(format, ...) creates a log entry without a timestamp.

DBGLOGA(format, ...) appends the formatted string to the previous log entry.

The utility macro DBGSTR(const char *s) returns string s or "(null)" when s == NULL.

Example

#include "debug.h"

int main(int argc, char *argv[])
{
  FILE *fd;
  DBGLOG("Program start");
  if ((fd = fopen("foo.bar", "r")) == NULL)
  {
    DBGLOG("Error %d: %s ", errno, DBGSTR(strerror(errno)));
    for (int i = 1; i < argc; ++i)
      DBGLOGA(" %s", argv[1]);
  }
  else
  {
    // OK, so go ahead to read foo.bar ...
    // ...
    fclose(fd);
  }
  DBGLOG("Program end");
}

Compiled with -DDEBUG this example logs the following messages in DEBUG.log:

140201/225654.692194   example.cpp:11   Program has started
140201/225654.692564   example.cpp:15   Error 2: No such file or directory
140201/225654.692577   example.cpp:17   Program ended

The first column records the date (140201 is February 1, 2014) and the time (225654 is 10:56PM + 54 seconds) with microsecond fraction. The second column records the source code file name and the line number of the DBGLOG command. The third column shows the printf-formatted message.

The DEBUG.log file is created in the current directory when it does not already exist.

Techniques used:

• Variadic macros with __VA_ARGS__.
• Standard predefined macros __FILE__ and __LINE__.
• Macro "stringification": expand content of macro DEBUG as a string in a macro body.
• #if DEBUG + 0 to test whether macro DEBUG is set to a value, since DEBUG is 1 when set without a value (for example at the command line).
• "" __VA_ARGS__ forces __VA_ARGS__ to start with a literal format string (printf security advisory).

Macro Definition Documentation

#define DBGLOG

(

...

)

(void)0

When compiled with -DDEBUG, adds a timestamped log entry with a printf-formatted message.

#define DBGLOGA

(

...

)

(void)0

When compiled with -DDEBUG, appends a printf-formatted message to the last log entry.

#define DBGLOGN

(

...

)

(void)0

When compiled with -DDEBUG, adds a log entry with a printf-formatted message.