Creating our own fprintf function in our library

This is a discussion on Creating our own fprintf function in our library within the C Programming forums, part of the General Programming Boards category; My Project is having 15000 files and around 2000000 lines of code, Developers used fprintf (sdterr,”%s”,string) function to generate logs, ...

  1. #1
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    Unhappy Creating our own fprintf function in our library

    My Project is having 15000 files and around 2000000 lines of code, Developers used fprintf (sdterr,”%s”,string) function to generate logs, Now we are asked to put time stamp on each log it is generated. Changing each file is not possible; we are planning to create our own “fprintf” function in one of our library. I’ll appreciate your guidance to solve this issue ( else some out of box ideas ).

    Thanks in advance.

    Baskar

  2. #2
    Kernel hacker
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    Don't post multiple times on the same subject.

    you can use vs(n)printf() to generate a string for output. A macro or replacement function (linked in before the standard library) should do the trick of replacing the standard printf.

    --
    Mats
    Compilers can produce warnings - make the compiler programmers happy: Use them!
    Please don't PM me for help - and no, I don't do help over instant messengers.

  3. #3
    and the hat of sweating
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    Code:
    #define fprintf   my_fprintf

  4. #4
    Just Lurking Dave_Sinkula's Avatar
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    7. It is easier to write an incorrect program than understand a correct one.
    40. There are two ways to write error-free programs; only the third one works.*

  5. #5
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    overriding glibc library

    I have found interesting solution to solve this issue. We have tried lot of solutions for this issue(i.e. logger daemon, message pipes etc ) finally everyone agreed for this. Just I want to share this information with Team.


    This a good way to override glibc (or any library) functions with our own version. This can be done without recompiling our source and glibc source. It is a thrill of writing our own version of glibc functions. This will be helpful to debug our code with out source compilation.



    We have created own “fprintf” and “printf” functions and created “.so” for that . Please refer attached file.

    “.so” creation

    gcc -shared -o libfuncs.so libfuncs.c

    copy this “so” to libs


    export LD_PRELOAD=/libs/libfuncs.so

    Now start your application


    Code:
    ///libfunc.c
    
    // Test code for fprintf time stamp  
    // This will add  File name, Line number & Time stamp on stderr
    // [Baskar]   time stamp test
    
    
    #include <stdio.h>
    #include <string.h> 
    #include <stdarg.h>
    #include <time.h>
    #include <stdlib.h>
    #include <sys/time.h>
    
    #define DATA_SIZE	1024
    #define DATE_TIME_SIZE 256
    #define ERROR  -1
    
    
    
    //************************ Method Header ****************************
    // Method Name        : fprintf [SJM]
    // Purpose            : Wrapper for time stamp impl.
    //                      
    //                      
    // Author             : Baskar
    // Exceptions Thrown  : None
    //*******************************************************************
    
    int  fprintf(FILE *fp,const char *format,...)
    {
    		int l_nNumOfChars=0;
    		va_list args;
    		va_start(args, format);
    		//If it is Standard error or Standard out………. proceed further
    		if(fp == stderr || fp == stdout )
    		{
    			 char l_carrTmpData[DATA_SIZE]={0};
    			 char l_carrTmpDateTime[DATE_TIME_SIZE]={0};
    			 char l_carrTmpDataAndTime[DATA_SIZE + DATE_TIME_SIZE]={0};
    			
    			 struct timeval timeNalue;
    			 if( gettimeofday(&timeNalue, NULL) != ERROR )
    			 {
    				struct tm *st_pTimeSt = localtime(&timeNalue.tv_sec);
    			
    				 if(st_pTimeSt)
    				 {
    					snprintf(l_carrTmpDateTime,DATE_TIME_SIZE, "%02d/%02d/%04d %02d:%02d:%02d:%02d",
    						st_pTimeSt->tm_mday, st_pTimeSt->tm_mon+1, st_pTimeSt->tm_year+1900,st_pTimeSt->tm_hour, st_pTimeSt->tm_min, st_pTimeSt->tm_sec,(timeNalue.tv_usec/1000));
    				 }
    				
    			 }
    			 vsnprintf(l_carrTmpData, DATA_SIZE, format, args);
    
    			if(l_carrTmpData[0] == '\n' )
    			{
    				l_carrTmpData[0]=' ';
    				snprintf(l_carrTmpDataAndTime,DATA_SIZE + DATE_TIME_SIZE,"\n%s-%s",l_carrTmpDateTime,l_carrTmpData );
    
    			}
    			else
    			{
    				snprintf(l_carrTmpDataAndTime,DATA_SIZE + DATE_TIME_SIZE,"%s - %s",l_carrTmpDateTime,l_carrTmpData );
    			}
    
    			l_nNumOfChars = fwrite(l_carrTmpDataAndTime,1,strlen(l_carrTmpDataAndTime),stderr);
    
    		}
    		else // else write to mentioned file
    		{
    			
    			l_nNumOfChars = vfprintf(fp, format, args);
    			
    		}
    		va_end(args);
    		return l_nNumOfChars;
    }		
    //************************ Method Header ****************************
    // Method Name        : printf [SJM]
    // Purpose            : Wrapper for time stamp impl.
    //                      
    //                      
    // Author             : Baskar
    // Exceptions Thrown  : None
    //*******************************************************************
    int printf (const  char *format, ...)
    {
    		int l_nNumOfChars=0;
    		char l_carrTmpData[DATA_SIZE]={0};
    		char l_carrTmpDateTime[DATE_TIME_SIZE]={0};
    		char l_carrTmpDataAndTime[DATA_SIZE + DATE_TIME_SIZE]={0};
    		struct timeval timeNalue;
    
    		va_list args;
    		va_start(args, format);
    		
    		if( gettimeofday(&timeNalue, NULL) != ERROR )
    		{
    			struct tm *st_pTimeSt = localtime(&timeNalue.tv_sec);
    			if(st_pTimeSt)
    			{
    				snprintf(l_carrTmpDateTime,DATE_TIME_SIZE, "%02d/%02d/%04d %02d:%02d:%02d:%02d",
    						st_pTimeSt->tm_mday, st_pTimeSt->tm_mon+1, st_pTimeSt->tm_year+1900,st_pTimeSt->tm_hour, st_pTimeSt->tm_min, st_pTimeSt->tm_sec,(timeNalue.tv_usec/1000));
    			}
    
    		}
    		vsnprintf(l_carrTmpData, DATA_SIZE, format, args);
    		va_end(args);
    
            if(l_carrTmpData[0] == '\n' )
    		{
    			l_carrTmpData[0]=' ';
    			snprintf(l_carrTmpDataAndTime,DATA_SIZE + DATE_TIME_SIZE,"\n%s - %s",l_carrTmpDateTime,l_carrTmpData );
    
    		}
    		else
    	    {
    			snprintf(l_carrTmpDataAndTime,DATA_SIZE + DATE_TIME_SIZE,"%s - %s",l_carrTmpDateTime,l_carrTmpData );
    		}
    		
    
    		
    		l_nNumOfChars = fwrite(l_carrTmpDataAndTime,1,strlen(l_carrTmpDataAndTime),stderr);
    
    		return 	l_nNumOfChars;		
    		
    }
    
    
    /// Add required functions.../.

  6. #6
    Captain Crash brewbuck's Avatar
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    I don't like this solution because it makes it impossible to call printf() or fprintf() in a normal way, even if you wanted to. Why not just make a special logging function log_printf() and call this instead of calling printf() directly? It would also actually have a chance of working correctly on other platforms.

  7. #7
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    Hi,
    We don't want to compile our legacy code. It required lot of testing effort.. This technique is useful for Legacy app enhancements. This will override dynamically linked APIs

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