/* Code for exercise 6.16. |  | "C++ Solutions--Companion to The C++ Programming Language, Third Edition" | by David Vandevoorde; Addison-Wesley 1998; ISBN 0-201-30965-3. | | Permission to use, copy, modify, distribute and sell this software | and its documentation for any purpose is hereby granted without fee. | The author makes no representations about the suitability of this | software for any purpose.  It is provided "as is" without express or | implied warranty. `----------------------------------------------------------------------*/#include <limits>#include <stdexcept>#include <string>#include <stdio.h>#if 0using std::domain_error;using std::range_error;using std::string;#endifnamespace {   inline int digit(char c, int base) {      int value;      switch (c) {         case '0': value = 0; break;         case '1': value = 1; break;         case '2': value = 2; break;         case '3': value = 3; break;         case '4': value = 4; break;         case '5': value = 5; break;         case '6': value = 6; break;         case '7': value = 7; break;         case '8': value = 8; break;         case '9': value = 9; break;         case 'a': case 'A': value = 10; break;         case 'b': case 'B': value = 11; break;         case 'c': case 'C': value = 12; break;         case 'd': case 'D': value = 13; break;         case 'e': case 'E': value = 14; break;         case 'f': case 'F': value = 15; break;         default:            throw domain_error(string("invalid digit"));      }      if (value>=base)         throw domain_error(string("invalid digit"));      return value;   }   inline char next_char(char const *&p) {      if (*p!='\\') // \ is special; hence '\\'         return *p++;      else { // 3 octal digits:                  int char_value = digit(p[1], 8)*64                         +digit(p[2], 8)*8                         +digit(p[3], 8);         if (char_value>std::numeric_limits<char>::max()          or char_value<std::numeric_limits<char>::min())            throw domain_error(string("not a char"));         p += 4; // backslash and 3 octal digits         return char_value;      }   }   void load_first_digit(char const *&s, int &value,                         bool &is_negative, int &base) {      char c1 = next_char(s);      is_negative = c1=='-';      if (c1=='-' || c1=='+')         c1 = next_char(s);      if (c1=='\0') { // "", "-" and "+" are illegal         throw domain_error(string("invalid input"));      } else if (c1!='0') {         base = 10;      } else {         char const *p = s;         char c2 = next_char(p);         if (c2=='x' || c2=='X') { // "0x..."?            base = 16;            s = p;            c1 = next_char(s);         } else { // c2!='x' and c2!='X'             base = 8; // I.e., even "0" is treated as octal         }      }      value = digit(c1, base);   }} // End unnamed namespace (helper functions)int atoi(char const *s) {   int value, base;   bool is_negative;   load_first_digit(s, value, is_negative, base);    while (char c = next_char(s)) {      if (value>std::numeric_limits<int>::max()/base)         throw range_error(string("out-of-range"));      value *= base;      int d = digit(c, base);      if (value>std::numeric_limits<int>::max()-d)         throw range_error(string("out-of-range"));      value += d;   }   return is_negative? -value: value;}int main() {   printf("atoi(\"123\") = %d\n", atoi("123"));   printf("atoi(\"0123\") = %d\n", atoi("0123"));   printf("atoi(\"0x123\") = %d\n", atoi("0x123"));}