Introduction

Under UNIX/Linux platform, program coredump generates a core file, we can analyze the core file and determine what's wrong in our program. The core file records the function call stack (e.g. under gdb you can use bt command to see backtrace), that is mostly information for us to troubleshooting.

When I debug my program, I try to record the function call stack in program debug log to help me diagnose the program's defect. Fortunately, C++ gives us a simple way to implement this.

Rational

Just use C++ constructor/destructor semantic, we can make our own trace class. At the function entrance, we declare a local variable, it will invoke the constructor immediately, when leaving the function, the local variable will be destroyed and call destructor. That's all. what we need to do is implement a class's constructor and destructor. This rational is simple enough, but this way sometimes can help us a lot.

The complete code is as follows:

// trace.hpp
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#include <stdarg.h>
#include <string>

#define CM_TRACE_FILE(trace_file)	cm::Trace::LogToFile(trace_file)

#define CM_TRACE_FUNC(func_name)    cm::Trace __CM_TRACE__(func_name, "()")
#define CM_TRACE_FUNC_ARG1(func_name, argfmt, arg)   \
            cm::Trace __CM_TRACE__(func_name, argfmt, arg)
#define CM_TRACE_FUNC_ARG2(func_name, argfmt, arg1, arg2)   \
            cm::Trace __CM_TRACE__(func_name, argfmt, arg1, arg2)
// more macros define....

namespace	cm
{
    class	Trace
    {
    public:
    	explicit Trace(char *func_name, const char* argsfmt, ...)
    	{
            char fmt[256] ={0};
            sprintf(fmt, "%s%s", func_name, argsfmt);
    	    va_list arglist;
    	    va_start(arglist, argsfmt);
    		LogMsg(depth_, depth_ * 2, fmt,  arglist);
    		va_end(arglist);
    		++depth_;
    	}

    	~Trace()
    	{
    		--depth_;
    	}

    	/// special the global log file.
    	void static LogToFile(const char *trace_file)
    	{
    		trace_file_ = trace_file;
    	}

    private:
    	void LogMsg(int depth, int align, const char *fmt, va_list args)
    	{
    		FILE	*fp = fopen(trace_file_.c_str(), "a+");
    		if (fp == NULL)
    		{
    			return;
    		}


    		time_t		curTime;
    		time(&curTime);

    		char	timeStamp[32] = { 0 };
    		strftime(timeStamp, sizeof(timeStamp), 
				"%Y%m%d.%H%M%S", localtime(&curTime));

    		// only log the timestamp when the time changes
    		unsigned int len = fprintf( fp, "%s %*.*s> (%d)",
    				(last_invoke_time_ != curTime) ? 
				timeStamp : "               ",
    				2 * depth,
    				2 * depth,
    				nest_,
    				depth);
    		last_invoke_time_ = curTime;
    		len += vfprintf(fp, fmt, args);
    		len += fwrite("\n", 1, 1, fp);
    		fflush(fp);
    		fclose(fp);
    	}

    private:
    	// the debug trace filename
    	static std::string	trace_file_;

    	// function call stack depth
    	static int			depth_;
    	static const char*  nest_;
    	static time_t       last_invoke_time_;
    };

    std::string Trace::trace_file_  = "";
    int         Trace::depth_       = 0;

    // arbitrarily support nesting 34 deep for no particular reason
    const char* Trace::nest_        = 
	"| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | ";
    time_t      Trace::last_invoke_time_ = 0;
}	// end namespace cm
#endif // CM_TRACE_20060209_HPP

Using the Code

First you need to call CM_TRACE_FILE() to special debug log filename, then at function entrance, call CM_TRACE(). Here is an example.

#include "cm/trace.hpp"

void foo()
{
	CM_TRACE_FUNC("foo");
}

void bar(int x)
{
	CM_TRACE_FUNC_ARG1("bar", "(%d)", x);
	foo();
}

void foobar(int x, const char* s)
{
    CM_TRACE_FUNC_ARG2("foobar", "(%d, %s)", x, s);
    bar(789);
}

void foobar3(int x, int y, double z)
{
    CM_TRACE_FUNC_ARG3("foobar3", "(%d, %d, %f)", x, y, z);
    foobar(123, "4546");
}

int main()
{
    CM_TRACE_FILE("./trace.log");
    CM_TRACE_FUNC("main");
    foo();
    bar(23);
    foobar(33, "char");
    foobar3(12, 23, 34.45);
    return 0;
}

Then open `trace.log', use your favourite editor. At the end of file, you will see the following:

20060211.132431 > (0)main()
                | > (1)foo()
                | > (1)bar(23)
                | | > (2)foo()
                | > (1)foobar(33, char)
                | | > (2)bar(789)
                | | | > (3)foo()
                | > (1)foobar3(12, 23, 34.450000)
                | | > (2)foobar(123, 4546)
                | | | > (3)bar(789)
                | | | | > (4)foo()

Conclusion

The rational in this article is simple, but we can write simple code do useful things.

Revision History

v1.00 Feb 4, 2005. Mockey
- Original article
v1.01 Feb 11 2005. Mockey
- Change fstream to FILE*
- Change string to sprintf for more efficiency. Thanks Jon Wold's comment
- Rename CM_TRACE to CM_TRACE_FUN and add CM_TRACE_FUN_ARGx macros.
- Add feature to log the function call arguments.

A Simple C++ Function Call Stack Trace Utility