C语言模拟实现库函数atoi

#include 
#include
#include
int my_atoi(const char* str,int state)
{
	int flag = 0;
	if (str == NULL)
		return 0;
	if (*str == '\0')
		return 0;
	while (isspace(*str))//去除空格
	{
		str++;
	}
	if (*str == '+')
	{
		flag = 1;//正数
		str++;
	}
	else if (*str == '-')
	{
		flag = -1;//负数
		str++;
	}
	long long ret = 0;
	
	while (isdigit(*str))//调用库函数isdigit，判断*str是否为数字 
	{
		ret = ret * 10 + flag*(*str - '0');
		if (ret > INT_MAX || ret < INT_MIN)//ret越界
		{
			ret = 0;
			return (int)ret;
		}
		str++;
	}
	if (*str == '\0')
	{
		state = 0;
		return (int)ret;
	}
	return (int)ret;
}
int main()
{
	char*p1 = "  -123abc45r67SDF";
	int state = 1;
	int ret = my_atoi(p1,state);
	printf("%s\n", p1);
	printf("%d\n", ret);
	return 0;
}