Question

I am writing this code to convert a hex entry into its integer equivalent. So A would be 10 and B would be 11 etc. This code acts weirdly, in that it seg. faults at random locations and including an extra newline character at times will get it to work. I am trying to debug it, just so I can understand what I am doing wrong here. Can anyone take a look and help me here ? Thanks a lot for your time.

/* Fixed working code for anyone interested */

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


            unsigned int hextoint(const char temp[])
            {

            int i;
            int answer = 0;
            int dec;
            char hexchar[] = "aAbBcCdDeEfF" ;


            for ( i=0; temp[i] != '\0'; i++ )
            {

                if ( temp[i] == '\0')
                {

                    return ;        
                }

                if (temp[i] == '0' || temp[i] == 'x' || temp[i] == 'X' )
                {       
                    printf("0");
                    answer = temp[i];
                }

                // compare each temp[i] with all contents in hexchar[]
                int j;
                int a = temp[i];
                for ( j=0; hexchar[j] != '\0'; j++)
                {
                    if ( temp[i] == hexchar[j] )
                    {
                    answer *= 16;
                    answer = answer + 10 + (j/2);
  //                    printf("%d\n",answer );
                    break;      
                    }
                }

            }

            return answer;  

            }


            main()
            {
            char *test[] = 
            {   "bad",
                "aabbdd"
                "0100",
                "0x1",
                "0XA",
                "0X0C0BE",
                "abcdef",
                "123456",
                "0x123456",
                "deadbeef", 
                "zog_c"
            };

            int answer=0;

            // Calculate the number of char's.
            int numberOfChars;
            numberOfChars = sizeof test /sizeof test[0];

            printf("main():Number of chars = %d\n",numberOfChars);
            int i;
            // Go through each character and convert Hex to Integers.
            for ( i = 0; i<numberOfChars;i++)
            {
                // Need to take the first char and then go through it and convert            
                                        it.
                answer = hextoint(test[i]);
                printf("%d\n",answer ); 
            }


            }

Answer 1

Let’s take a look.

unsigned int hextoint(const char temp[])
{
    int i;
    int answer = 0;
    char hexchar[] = "aAbBcCdDeEfF" ;

    for ( i=0; temp[i] != '\0'; i++ )
    {
        printf("In here");
        printf("%c\t",temp[i] );
    }

    return answer;  
}

This doesn’t seem to even try to do any conversion. It should always return 0, since answer is never assigned any other value. Normally, you’d do something like:

for (i=0; input[i] != '\0'; i++) {
    answer *= 16;
    answer += digit_value(input[i]);
}
return answer;

Where digit_value (obviously enough) returns the value of an individual digit. One way to do this is:

int digit_value(char input) { 
    input = tolower(input);
    if (input >= '0' && input <= '9')
        return input - '0';
    if (input >= 'a' && input <= 'f')
        return input - 'a' + 10;
    return -1; // signal error.
}

Then, looking at main:

main()
{

Depending on the “implicit int” rule is generally poor practice, at least IMO. It’s much better to specify the return type.

// Calculate the number of char's.
int numberOfChars;
numberOfChars = sizeof test /sizeof test[0];

This actually calculates the number of strings, not the number of chars.

for ( i = 0; i<=numberOfChars;i++)

Valid subscripts run from 0 through the number of items – 1, so this attempts to read past the end of the array (giving undefined behavior).