how to write a hex value to file ?

This is a discussion on how to write a hex value to file ? within the C Programming forums, part of the General Programming Boards category; 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'; ...

  1. #1
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    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

  2. #2
    CSharpener vart's Avatar
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    Code:
    char *buff = "efa49b4d";
    fprintf(f,"%s", buff);
    Code:
    unsigned int t = 0xefa49b4d;
    fprintf(f,"%08x",t);
    The first 90% of a project takes 90% of the time,
    the last 10% takes the other 90% of the time.

  3. #3
    Guest Sebastiani's Avatar
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    Or even:

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

  4. #4
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    unfortunatlly the values Buff[8] calculated with one library QuickCrc from SlavaSoft Inc.

    i must convert it and then write to file .

    thhanks

  5. #5
    CSharpener vart's Avatar
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    Quote Originally Posted by noobe View Post
    unfortunatlly the values Buff[8] calculated with one library QuickCrc from SlavaSoft Inc.

    i must convert it and then write to file .

    thhanks
    So? what is the problem? "%8.8s" format of fprintf should work fine
    The first 90% of a project takes 90% of the time,
    the last 10% takes the other 90% of the time.

  6. #6
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    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 ?

  7. #7
    Guest Sebastiani's Avatar
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    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;
    }

  8. #8
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    Use strtol() or strtoul() to convert a hex string to a number. Then use fputc() or fwrite() to write the numbers to a file.
    It is too clear and so it is hard to see.
    A dunce once searched for fire with a lighted lantern.
    Had he known what fire was,
    He could have cooked his rice much sooner.

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