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Convert hexadecimal string to int

Posted on 2004-10-03
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How to convert a string like "1e234", located in a file, to int format using standard C functions?
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Question by:epsa
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Jaime Olivares earned 125 total points
Comment Utility
Just use sscanf:

int number;
char *str =  "1e234";   /* test string */

sscanf(str, "%x", &number);

good luck,
Jaime.
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Expert Comment

by:jkr
Comment Utility
You'd use 'strtol()', it handles all numeric bases:

Example

/* STRTOD.C: This program uses strtod to convert a
 * string to a double-precision value; strtol to
 * convert a string to long integer values; and strtoul
 * to convert a string to unsigned long-integer values.
 */

#include <stdlib.h>
#include <stdio.h>

void main( void )
{
   char   *string, *stopstring;
   double x;
   long   l;
   int    base;
   unsigned long ul;
   string = "3.1415926This stopped it";
   x = strtod( string, &stopstring );
   printf( "string = %s\n", string );
   printf("   strtod = %f\n", x );
   printf("   Stopped scan at: %s\n\n", stopstring );
   string = "-10110134932This stopped it";
   l = strtol( string, &stopstring, 10 );
   printf( "string = %s", string );
   printf("   strtol = %ld", l );
   printf("   Stopped scan at: %s", stopstring );
   string = "10110134932";
   printf( "string = %s\n", string );
   /* Convert string using base 2, 4, and 8: */
   for( base = 2; base <= 8; base *= 2 )
   {
      /* Convert the string: */
      ul = strtoul( string, &stopstring, base );
      printf( "   strtol = %ld (base %d)\n", ul, base );
      printf( "   Stopped scan at: %s\n", stopstring );
   }
}


Output

string = 3.1415926This stopped it
   strtod = 3.141593
   Stopped scan at: This stopped it

string = -10110134932This stopped it   strtol = -2147483647   Stopped scan at: This stopped itstring = 10110134932
   strtol = 45 (base 2)
   Stopped scan at: 34932
   strtol = 4423 (base 4)
   Stopped scan at: 4932
   strtol = 2134108 (base 8)
   Stopped scan at: 932


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Expert Comment

by:ankuratvb
Comment Utility
>How to convert a string like "1e234", located in a file,to int?

Adding to what jaime said,use fscanf() to directly read from the file and convert to int.
FILE *fp;

fscanf(fp,"%x",&number);

You'd like to use strtol() etc. for better error checking though.
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Author Comment

by:epsa
Comment Utility
Unix doesn't support Strtol() :(
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LVL 55

Expert Comment

by:Jaime Olivares
Comment Utility
any variant of scanf() family will be OK and very portable.
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