Thread: how to write a hex value to file ?

how to write a hex value to file ?

Code:

void samplecode(void){ 

FILE *fp;
char buff[8];

fp=fopen("tmp.bin","r+w+b");

buff[0]='e';
buff[1]='f';
buff[2]='a';
buff[3]='4';
buff[4]='9';
buff[5]='b';
buff[6]='4';
buff[7]='d';

fwrite(buff,1,8,fp); //??????????????????

fclose(fp);
}

I want to write 'ef' hex value to tmp.bin with buff but I can't know how do it .
i want to write "efa49b4d" hex value to tmp.bin .

Thanks for helps

Or even:

Code:

char buff[4];
buff[0]=0xef;
buff[1]=0xa4;
buff[2]=0x9b;
buff[3]=0x4d;

unfortunatlly the values Buff[8] calculated with one library QuickCrc from SlavaSoft Inc.

i must convert it and then write to file .

thhanks

really i want write "ef" in one byte but with %s save e in one byte and f in one byte with saving assci cods . assci code of "e" saved . and so on .

I want save the string with8 ellement in 4 byte with convering every 2 ellement in one hex byte .

do you konw my problem ?

I was trying to think of a library function to do this, but couldn't really think of any. Perhaps something like this would work for you:

Code:

size_t hex_string_to_hex_data( char const* txt, void* dst, size_t max )
{
	unsigned char
		nyb,
		* cvt = ( unsigned char* )dst;
	size_t
		cnt,
		idx, 	
		len = strlen( txt ), 
		hlf = len / 2;
	if( len == 0 || len % 2 != 0 || hlf > max )
		return 0;
	for( idx = 0; idx < len; idx += 2, ++cvt )
	{
		*cvt = 0;
		for( cnt = 0; cnt < 2; ++cnt )
		{
			nyb = tolower( txt[ idx + cnt ] );
			if( isdigit( nyb ) )
				nyb -= '0';
			else if( nyb >= 'a' && nyb <= 'f' )
				nyb = ( nyb - 'a' ) + 10;
			else 
				return 0;	
			*cvt |= nyb << ( ( 1 - cnt ) << 2 );
		}
	}
	return hlf;
}