/*

 atoi算法，要求完美版

 有两种，一种是用longlong，一种是真用int

 “”

 "  "

 “-”

 “+”

 “  -23”

 “  +23”

 “12a"

 "abc"

 越界情况

 */

 #include <iostream>

 using namespace std;

 //方法一用 long long 取巧

 int atoi(const char * str,bool & flag)

 {

     long long result=;

     int tmp;

     int sign=;

     if(str==NULL)

     {

         flag=false;

         return ;

     }

     while(isspace(*str))

         str++;

     //if(*str=='\0')

     //{

     //    flag=false;

     //    return 0;

     //}

     if(*str=='+'||*str=='-')

     {

         if(*str=='-')

             sign=-;

         str++;

     }

     if(*str=='\0')                     //”    “和”+“ ，”-“的情况

     {

         flag=false;

         return ;

     }

     while(*str>=''&&*str<='')

     {

         tmp=*str-'';

         result=result*+tmp;

         if(sign==-)

         {

             if(result->INT_MAX)           //这里注意，如果是INT_MAX+1，系统或默认转换成int，导致越界，所以用result-1，result是longlong不会越界

             {

                 result=INT_MAX+;

                 flag=false;

                 break;

             }

         }

         else if(result>INT_MAX)

         {

             result=INT_MAX;

             flag=false;

             break;

         }

         str++;

     }

     if(*str=='\0')

         flag=true;

     else

         flag=false;

     return sign*result;

 }

 //方法二 用int

 int atoi2(const char * str ,bool & flag)

 {

     int result=;

     int sign=;

     int tmp;

     int MAX_DIV=INT_MAX/;

     int MAX_R=INT_MAX%;

     int MIN_R=MAX_R+;   //或者为MIN_R=-(INT_MIN%10);    //如果用(INT_MAX+1)%10就错了，直接加的时候越界

     int MIN_DIV=(INT_MAX)/;        

     //july用的是max=(int)((unsigned)~0>>1);

     //min_r=(int)(((unsigned)~0>>1+1)%10);

     if(str==NULL)

     {

         flag=false;

         return result;

     }

     while(isspace(*str))

         str++;

     if(*str=='+'||*str=='-')

     {

         if(*str=='-')

             sign=-;

         str++;

     }

     if(*str=='\0')

     {

         flag=false;

         return result;

     }

     while(*str>=''&&*str<='')

     {

         int tmp=*str-'';

         if(sign==)

         {

             if(result>MAX_DIV||(result==MAX_DIV&&tmp>MAX_R))

             {

                 result=INT_MAX;

                 flag=false;

                 return result;

             }

         }

         else if(result>MIN_DIV||(result==MIN_DIV&&tmp>MIN_R))

         {

             result=INT_MIN;                                               //result直接为最小-2147483648，直接返回了

             flag=false;

             return result;

         }

         result=result*+tmp;

         str++;

     }

     if(*str=='\0')

         flag=true;

     else

         flag=false;

     return sign*result;

 }

 int main()

 {

     char * str[]={""," ","abc","","  -1234","   +34","  12bc","+","-","+++","","","+2147483648","-2147483648","-2147483649","+12123131312432342","   -122323434534534654"};

     //cout<<INT_MAX<<endl;

     int n=;

     bool flag;

     for(int i=;i<n;i++)

     {

         int tmp=atoi2(str[i],flag);

         if(tmp==)

         {

             if(flag==false)

                 cout<<str[i]<<" 错误数据转换为： "<<tmp<<endl;

             else

                 cout<<str[i]<<" 转换为: "<<tmp<<endl;

         }

         else

         {

         cout<<str[i]<<" 转换为: "<<tmp<<endl;

         }

     }

     system("pause");

 }