Note: please do not reprint;

(I) function introduction

The atoi() function scans the str string of the parameter, skips the preceding blank characters (such as space, tab indentation, etc., which can be detected through the isspace() function), and does not start the conversion until it meets a number or a positive and negative sign, and then ends the conversion when it encounters a non number or the end of the string ('\ 0'), and returns the result. Finally, the converted integer is returned; if STR cannot be converted to int or STR is an empty string, then 0 will be returned.

(II) code implementation

#include <iostream>
#include <string>
#include <map>
#include <utility>
using namespace std;
class Secure
{
public:
	Secure() //Initialization
	{
		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) //Remove the cases where the first parameter is not 0, O, O, or
			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)//Decimal processing function
	{
		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 function is used to judge whether it is a digital character. Try to use library function.
			{
				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) //Octal processing function
	{
		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) //Hexadecimal processing function
	{
		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;
}