reporting logging error messages

Question

Hello,

I would like to log messages and have decided to use the following format. However, as I am coming from C# I am not too sure how to go any further.

Basically I have the following messages that I would like to report on.

//Enum for the error codes
typedef enum
{
    DEV_START_ERR = 0,
    LIB_ERR,
    SDD_FAILURE,

LAST_ENTRY //This SHOULD be the last entry

} ErrorCode;

And using this for displaying but I am not sure how I would get this to work.

void log_msg(FILE *out, const char *fmt, ...)
{
    va_list ap;
    va_start(ap_fmt);
    vfprintf(out, fmt, ap);
    va_end(ap);
}

log_msg(stderr,
    "%s: Invalid range of %ld near line %d", __func__, range, __LINE__);

Many thanks for any advice,

Answer 1

Hello,

I don't think I very clear.

I have re-edited my source code with what I am having a problem.

typedef enum
{
    DEV_START_ERR,
    LIB_ERR,
    SDD_FAILURE,
    Last_ENTRY
} ErrorCode;

void log_MSG(FILE *out, const char *fmt, ...)
{
    va_list ap;
    va_start(ap, fmt);
    vfprintf(out, fmt, ap);
    va_end(ap);
}

int main(void)
{
    if(dev_start() != DEV_SUCCESS)
    {
        /* print error message here with the __func__, range, and __LINE__ */
        /* However, I am not sure how to add __func__, range, and the __LINE to print this on the screen */
        log_MSG(stderr, "Error code: %d", DEV_START_ERR);        
    }
    return 0;
}

Many thanks for any suggestions,

Answer 2

Hello,

Seeing from the code, log_MSG() is a "variable argument" function to log information, you just need to use log_MSG like the CRT function printf():

log_MSG(stderr, "Error Code: %d, Func: %s, Range: %s, Line: %d", DEV_START_ERR, "Function Name", "Range text", LineNo);

Sincerely,
Wesley

---

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Answer 3

Variable number of arguments and automatic parameters, eh?  Well it's not going to be pretty.

The preprocessor will help you get the function and line encoded into your call based on context.  But the variable arguments have to be double parenthesized.

Here's a little gem I've used a few times.

#include <stdarg.h>
#include <stdio.h>

#define LogMessage( x ) Context(__FUNCTION__,__LINE__) x

class Context
{
	const char* fn;
	int line;
public:
	Context( const char* fn, int line ) : fn(fn),line(line) {}
	void operator()( const char* format, ... )
	{
		printf( "%s(%d): ", fn, line );
		va_list args;
		va_start(args,format);
		vprintf( format, args );
		va_end( args );
		printf("\n");
	}
};


int main( void )
{
	LogMessage(( "%d %s %d", 100,  "hello", 200 ));
}

Answer 4

You could also use a variadic macro :

#define LogMessage( x, ... ) Something( __FUNCTION__,__LINE__, x, __VA_ARGS__ )

and define Something( const char* fn, int line, char* format, ... )
{
   printf( "%s(*%d): ", fn, line );
   va_list args;
   va_start( args, format );
   vprintf( format, args );
   va_end( args );
   printf( "\n" );
}