atoi代码实现

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atoi函数

atoi函数是实现数字字符串转整型数，实现代码的时候，要特别注意以下几点：

前面有空格，调过
要注意符号，即是正还是负数
非法输入
处理溢出

代码实现

int my_atoi(const char *str){    const char *s;    char c;    unsigned int cutoff;    int acc;    int neg, any, cutlim;    if(str == NULL)    {        errno = EINVAL;        return false;    }    s = str;    do{        c = *s++;    }while(c == ' ' || c == '\t');    if(c == '-'){        neg = 1;        c = *s++;     }    else    {        neg = 0;        if(c == '+')            c = *s++;    }    cutoff = neg? INT_MIN : INT_MAX;    cutlim = cutoff % 10;    cutoff /= 10;    acc = any = 0;    while(c >= '0' && c <= '9')    {        c -= '0';        if(acc > cutoff || (acc == cutoff && c > cutlim))        {            any = -1;            break;        }        else        {            any = 1;            acc *= 10;            acc += c;        }        c = *s++;    }    if(any < 0)    {        errno = ERANGE;        acc = neg? INT_MIN : INT_MAX;        return acc;    }    else if(any == 0)    {        errno = EINVAL;    }    else if(neg)    {        acc = -acc;    }    return acc;}

测试代码

void Test(const char *str){    errno = -1;    int result = my_atoi(str);    if(errno == EINVAL)        printf("str %s is : EINVAL \n",str);    else if(errno == ERANGE)        printf("str %s is : ERANGE  %d \n",str, result);    else        printf("str %s is : %d \n",str,result);}int main(int argc, char const *argv[]){    Test("");    Test("123");    Test("+123");    Test("-123");    Test("1a33");    Test("+0");    Test("-0");    //有效的最大正整数, 0x7FFFFFFF    Test("+2147483647");        Test("-2147483647");    Test("+2147483648");    //有效的最小负整数, 0x80000000    Test("-2147483648");        Test("+2147483649");    Test("-2147483649");    Test("+");    Test("-");    Test("10522545459");    Test("-10522545459");    Test("  +4488");    Test(" - 321");    return 0;}

结果输出如下：

str  is : EINVAL str 123 is : 123 str +123 is : 123 str -123 is : -123 str 1a33 is : 1 str +0 is : 0 str -0 is : 0 str +2147483647 is : 2147483647 str -2147483647 is : -2147483647 str +2147483648 is : ERANGE  2147483647 str -2147483648 is : -2147483648 str +2147483649 is : ERANGE  2147483647 str -2147483649 is : ERANGE  -2147483648 str + is : EINVAL str - is : EINVAL str 10522545459 is : ERANGE  2147483647 str -10522545459 is : ERANGE  -2147483648 str   +4488 is : 4488 str  - 321 is : EINVAL

参考资料

atoi函数的实现
http://arieshout.me/2012/03/implementation-of-atoi.html

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