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[SOLVED] To convert Hex string to interger using Keil C

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RyanHan

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Dear all,

I am trying to find a better way to convert a string of 4 Hex character to integer so that I can do the compare and do necessary action.

I am using a wireless communication to get ADC value from sensors and the return was string character of the value in Hex.

e.g. from 0000 to 2EEE.

I saw the atoi function in Keil C but it can only convert 0-9 and not A to F. Is there any function that can convert this 2 bytes data into integer?

Currently my method of conversion was quite lengthy. I will use a lookup table and convert all the string Hex into binary
e.g. 'F' (0x46) --> 0x0F, merge the individual 4 bit into a byte, then merge the 2 byte into an integer. Then only I can process the integer.

Anyone had a better idea? Pls share. Thanks a lot
 

Both KEIL C51 and MDK-ARM offer Standard C libraries, why not use sscanf()?

Code: 
#include <stdio.h>

int ahtoi( const char* hxstr )
{
    int number;
    sscanf( hxstr, "%x", &number );
    return number;
}


BigDog
 

Hi bigdog, can I ask about the function u write, I will received the Hex string in a data buffer, let's say the 4 hex to convert into int is in data[x-4], data[x-3], data[x-2] and data[x-1]. How can I write my function in the main so that I can get the return integer?

Is it like this
Code: 
unsigned int ADCvalue;

ADCvalue = ahtoi(data[x-4], data[x-3], data[x-2] and data[x-1]);
 

Hi to all,

The very good solution proposed by BigDog requires a null terminated string. So just add a 0x00 after the last hex digit and call the function with the pointer to the first hex digit.

If however the sscanf() adds a long code, you can try using a 'homemade' conversion look like:
Code: 
unsigned short hex_to_short(unsigned char* buffer)
{
   unsigned char k,i;
   unsigned short  n; 
   
   for(i=0;i<4;i++)
   {
      k=*(buffer+i)-48;
      if (k>9)           //hex digit not a number 
          k-=7;
      k&=0x0f;       //lowercase or wrong hex digit
      n=(n<<4) | k;
   }
   return n;
}
 
Hi Bigdog,

I try using data buffer to individually called your function. But it still give me illegal pointer conversion. Sorry, really not so good at pointer. Can advise?

Code: 
ADCvalue = 0;
for (i=0; i<4; i++)
	{
		ADCvalue = ADCvalue + ahtoi(Data[i]);
	}

- - - Updated - - -

Hi Alex_r,

Great thanks to you. You code is simple to understand for novice like me. I had try it and it works for my application and I understand the concept behind your program. This is my test program and I can convert the string "2EEE" into unsigned int 2EEE. Thanks again

Code: 
unsigned int Stringhex_to_hex(unsigned char* buffer)
{
   unsigned char k,i;
   unsigned int  n; 
   
   for(i=0;i<4;i++)
   {
      k=*(buffer+i)-48;
      if (k>9)           //hex digit not a number 
          k-=7;
      k&=0x0f;       //lowercase or wrong hex digit
      n=(n<<4) | k;
   }
   return n;
}

void main (void)
{
 	unsigned int ADCvalue;
	unsigned char Data[4];

	Data[0] = '2';
   	Data[1] = 'E';
	Data[2] = 'E';
	Data[3] = 'E';

	ADCvalue = Stringhex_to_hex(&Data[0]);
	
}
 

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