Question:
Given a string that contains hexadecimal number, write a function htoi() that returns the equivalent integer.
// Here is one function
int getValue(char const* hexString, int const radix)
{
int loopIndex; // Loop iterator
int signFlag = 1; // Keeps track of sign
signed int retValue = 0; // Final value
int currentDigit; // Current digit under process
int len = strlen(hexString); // Lenght of string
// Check for sign
if(hexString[0] == '-')
{
// Advance the base
hexString++;
// Remove '-' from count
len--;
// Sing is -ve
signFlag = -1;
}
// Iterate from left to right
// Accumulate the weight of each digit upon occurance of next digit
for(loopIndex = 0; loopIndex < len; loopIndex++)
{
currentDigit = toupper(hexString[loopIndex]) - ASCII_ZERO;
// Is the digit between A through F?
if(currentDigit > 9)
{
// Adjust numerical value
currentDigit -= (ASCII_A - '9');
}
// Based on Horner's principle
retValue = retValue * radix + currentDigit;
}
// Flip the sign, if required
retValue *= signFlag;
// This is the final value
return retValue;
}Examples:
getValue("1011", 2); // Binary string to integer
getValue("12345", 10); // Decimal string to integer
getValue("ABCDE", 16); // Hexadecimal string to integer
Error handling is omitted.
1. Overflow and underflow (if string contains more than 10 characters on 32 bit machines, i.e. length = [32*log(2) + 1] digits in general, which is the characteristic).
2. Invalid String (containing unexpected characters).
3. String not terminated with NUL character.
4. String is NULL.
5. What if a kernel space buffer is passed as hex string?
6. Is it reentrant?
7. Who will be the consumers of the function, and possible ways of misusing it?
8. What changes are required if wide character buffer (Unicode) is passed (portability issue).
9. Any optimizations without compromising on the functionality.
