【C++】实现atoi函数

注：请勿转载；

（一）函数介绍

        atoi() 函数会扫描参数 str 字符串，跳过前面的空白字符（例如空格，tab缩进等，可以通过 isspace() 函数来检测），直到遇上数字或正负符号才开始做转换，而再遇到非数字或字符串结束时('\0')才结束转换，并将结果返回。最后返回转换后的整型数；如果 str 不能转换成 int 或者 str 为空字符串，那么将返回 0。

（二）代码实现

#include <iostream>
#include <string>
#include <map>
#include <utility>
using namespace std;
class Secure
{
public:
	Secure() //初始化
	{
		warn = 0;
		note = "";
		valma.insert(make_pair('I', 1));
		valma.insert(make_pair('l', 1));
		valma.insert(make_pair('z', 2));
		valma.insert(make_pair('Z', 2));
		valma.insert(make_pair('o', 0));
		valma.insert(make_pair('O', 0));			
	}

	int find(char ch)
	{
		if (valma.end() == valma.find(ch))
		{
			return -1;
		}
		warn++;
		note += ch;
		return valma.find(ch)->second;
	}
		
	void showRecord()
	{
		if (warn == 0)
			return;

		cout << "warn:" << warn << endl;
		for (unsigned int i = 0; i < note.size(); i++)
		{
			cout << valma.find(note[i])->second << " - " << note[i] << endl;
		}
	}

	void clear()
	{
		warn = 0;
		note = "";
	}
	
private:
	int warn;
	string note;
	map<char, int> valma;
};

class Transverter
{
public:
	void my_atoi()
	{
		Secure secure;
		string str, constr = "y";
		while (constr[0] == 'y')
		{
			constr.clear();
			cout << "input str: ";

			getline(cin, str);
			int ans = trans(str, secure);

			cout << "out put: " << ans << endl;
			secure.showRecord();
			cout << "continue? yes or no:";

			getline(cin, constr);
			str.clear();
			secure.clear();
			cout << "-------cut------cut------" << endl;
		}
	}

private:

	bool find(Secure &secure, char ch)
	{
		string ostr = "O0o";
		if (ostr.find(ch) == ostr.npos) //去除第一个参数不为0、O、o、三种情况
			return false;
		if (ch != '0')
			secure.find(ch);
		return true;
	}

	int checkVal(long long val, int flag)
	{
		if (val >= INT_MAX)
		{
			if (flag == 1)
				return INT_MAX;
			return INT_MIN;
		}
		else
		{
			return val*flag;
		}
	}

	int str_to_digit(string str, int flag, Secure &secure)//10进制处理函数
	{
		long long val = 0;
		for (unsigned int i = 0; i < str.size() && val != INT_MAX; i++)
		{
			if (str[i] == '.' && isdigit(str[i + 1]))
			{
				val = (str[i + 1] - '0' < 5 ? val : val + 1);
				return checkVal(val, flag);
			}

			if (!isdigit(str[i]))//isdigit函数用来判断是否为数字字符，尽量使用库函数；
			{
				int tmp = secure.find(str[i]);
				if (tmp == -1)
					return 0;
				str[i] = '0' + tmp;
			}

			val = checkVal(val * 10 + str[i] - '0', 1);
		}
		return checkVal(val, flag);
	}

	int str_to_oce(string str, int flag, Secure &secure) //8进制处理函数
	{
		long long val = 0;
		for (unsigned int i = 0; i < str.size() && val != INT_MAX; i++)
		{
			if (str[i] == '8' || str[i] == '9')
				return 0;

			if (!isdigit(str[i]))
			{
				int tmp = secure.find(str[i]);
				if (tmp == -1)
					return 0;
				str[i] = '0' + tmp;
			}

			val = checkVal(val * 8 + str[i] - '0', 1);
		}
		return checkVal(val, flag);
	}

	int str_to_hex(string str, int flag, Secure &secure) //16进制处理函数
	{
		long long val = 0;
		for (unsigned int i = 0; i < str.size() && val != INT_MAX; i++)
		{
			if (!isxdigit(str[i]))
			{
				int tmp = secure.find(str[i]);
				if (tmp == -1)
					return 0;
				val = checkVal(val * 16 + tmp, 1);
			}
			else if (isdigit(str[i]))
				val = checkVal(val * 16 + str[i] - '0', 1);
			else
				val = checkVal(val * 16 + str[i] - 'A', 1);
		}
		return checkVal(val, flag);
	}

	int trans(string str, Secure &secure)
	{
		if (str.size() == 0)
			return 0;

		unsigned int i = 0;
		int flag = 1, ans = 0;

		while (i < str.size() && isspace(str[i]))
		{
			i++;
		}
		if (str[i] == '-')
		{
			flag = -1;
			i++;
		}
		else if (str[i] == '+')
		{
			i++;
		}

		string new_str;
		if (find(secure, str[i]) && str[i + 1] == 'x' || str[i + 1] == 'X')
		{
			new_str = str.substr(i + 2, str.size() - i - 2);
			return str_to_hex(new_str, flag, secure);
		}
		secure.clear();

		if (find(secure, str[i]))
		{
			new_str = str.substr(i + 1, str.size() - i - 1);
			return str_to_oce(new_str, flag, secure);
		}
		else
		{
			new_str = str.substr(i, str.size() - i);
			return str_to_digit(new_str, flag, secure);
		}

	}
};

int main()
{
	Transverter transverter;
	transverter.my_atoi();
	return 0;
}