字符串转成数字

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

//////////////////////////////////////////////////////////////////////////
//1. 考虑 空字符
//2. 考虑 正负号
//3. 考虑 乱码字符
//4. 考虑 溢出  long long 最大值的取值范围
//5. C++有个函数atoi函数是转字符
///////////////////////////////////////////////////////////////////////////
long long StrToIntCore(const char *digit, bool minus);
enum Status {
    kValid = 0, //有效值
    KInvalid    //无效值
};

int  g_nStatus = kValid;  //默认为有效值

int StrToInt(const char *str)
{
    g_nStatus = KInvalid;
    long long num = 0;
    if (str != NULL && *str != '\0')
    {
        bool minus = false;
        //判断正负号
        if (*str == '+')
            str++;
        else if (*str == '-')
        {
            str++;
            minus = true;
        }

        if (*str != '\0')
        {
            num = StrToIntCore(str, minus);
        }
    }
    return (int)num;
}

long long StrToIntCore(const char *digit, bool minus)
{
    long long num = 0;
    while (*digit != '\0')
    {
        if (*digit >= '0' && *digit <= '9')
        {
            int flag = minus ? -1 : 1;//正负判断
            num = num * 10 + flag * (*digit - '0');//数字累加num
            if ((!minus && num > 0x7FFFFFFF) || (minus && num < (signed int)0x80000000))
            {
                num = 0;
                break;
            }
            digit++;
        }
        else
        {
            num = 0;
            break;
        }   
    }
    if(*digit == '\0')
    {
        g_nStatus = kValid;
    }
    return num;
}

void Test(char *string)
{
    int result = StrToInt(string);
    if (result == 0 && g_nStatus == KInvalid)
    {
        printf("the input %s is invalid \n.", string);
    }
    else
        printf("number for %s is %d \n", string, result);
}

int _tmain(int argc, _TCHAR* argv[])
{
    Test(NULL);
    Test("");
    Test("123");
    Test("-123");
    Test("+123");
    Test("la123");
    Test("+0");
    Test("-0");
    Test("+");
    Test("-");
    Test("+2147483647");
    Test("-2147483647");
    Test("+2147483648");
    Test("-2147483648");
    Test("+2147483649");
    Test("-2147483649");

    system("pause");
    return 0;
}