str2decint.cpp

int StrToDecInt(const char* str)    
{    
    static const int kMAX = (int)((unsigned)~0 >> 1);    
    static const int kMIN = -(int)((unsigned)~0 >> 1) - 1;    
    static const int kMAX_DIV = (int)((unsigned)~0 >> 1) / 10;    
    static const int kMIN_DIV = (int)((((unsigned)~0 >> 1) + 1) / 10);    
    static const int kMAX_R = (int)((unsigned)~0 >> 1) % 10;    
    static const int kMIN_R = (int)((((unsigned)~0 >> 1) + 1) % 10);   

    int n = 0;    
    int sign = 1;    
    int c;    

    while (isspace(*str))    
        ++str;    

    if (*str == '+' || *str == '-') {    
        if (*str == '-')    
            sign = -1;    
        ++str;    
    }

    while (isdigit(*str)) {    
        c = *str - '0';    
        if (sign > 0 && (n > kMAX_DIV || (n == kMAX_DIV && c >= kMAX_R))) {    
            n = kMAX;    
            break;    
        } else if (sign < 0 && (n > kMIN_DIV || (n == kMIN_DIV && c >= kMIN_R))) {    
            n = kMIN;    
            break;    
        }    
        n = n * 10 + c;    
        ++str;    
    }

    return sign > 0 ? n : -n;    
}