lex.cpp

#include <iostream>
#include <string>
#include <map>
#include <limits>
#include "global.h"
#include "support.h"

#pragma warning(disable:4996)

extern unsigned int numMax;
extern char ch;
extern long long value;
extern std::string ident;
extern int lineNo;
extern std::map<std::string, int> keywordTable;

int lex()
{
	std::map<std::string, int>::iterator res;
	ident.clear();
	while (true)
	{
		//跳过所有空白符
		while (isspace(ch))
		{
			if (ch == '\n')
			{
				lineNo++;
			}
			ch = getchar();
		}
		if (isalpha(ch))
		{
			//字母开头
			ident.clear();						//清除上一个ident留下的内容
			ident.append(sizeof(char), ch);     //将当前字符添加至ident中
			while (isalnum(ch = getchar()))
			{
				//如果当前是字母或者数字，则其应该是当前标识符中的一部分
				ident.append(sizeof(char), ch);  //将当前字符添加至ident中
			}
			//标识符结束
			res = keywordTable.find(ident);
			if (res != keywordTable.end())
			{
				//当前标识符是保留字
				print("Keyword", "Name", ident.c_str());
				return res->second;
			}
			return IDENT;
		}
		else if (isdigit(ch))
		{
			//数字
			ungetc(ch, stdin);
			scanf("%d", &value);
			scanf("%c", &ch);
			if (value > INT_MAX)
			{
				value = 0;
				error("The Number Is Too Big!");
			}
			return NUM;
		}
		else if (match(':'))
		{
			if (match('='))
			{
				//赋值号:=
				print("Sign", "Name", "BECOMES");
				return BECOMES;
			}
			else
			{
				//冒号':'
				print("Sign", "Name", "COLON");
				return COLON;
			}
		}
		else if (match('<'))
		{
			if (match('>'))
			{
				//不等号'<>'
				print("Sign", "Name", "NOT EQUAL");
				return NEQ;
			}
			else if (match('='))
			{
				//小于等于'<='
				print("Sign", "Name", "LESS OR EQUAL");
				return LEQ;
			}
			else
			{
				//小于号'<'
				print("Sign", "Name", "LESS");
				return LESS;
			}
		}
		else if (match('>'))
		{
			if (match('='))
			{
				//大于等于号'>='
				print("Sign", "Name", "GREATER OR EQUAL");
				return GEQ;
			}
			else
			{
				//大于号'>'
				print("Sign", "Name", "GREATER");
				return GREATER;
			}
		}
		else if (match('\''))
		{
			//字符处理
			ident.clear();
			while (isalnum(ch))
			{
				ident.append(sizeof(char), ch);
				ch = getchar();
			}
			if (match('\''))
			{
				ident.erase(ident.end()-1);
			}else
			{
				error("The Single Quotes don't match");
				//需要错误恢复吗？
			}
			if (ident.length() > 1)
			{
				error("There are too many characters in single quotes");
				ident.clear();
			}
			return CH;
		}
		else if (match('"'))
		{
			ident.clear();
			while (ch == 32 || ch == 33 || 35 <= ch && ch <= 126)
			{
				//引号内的字符
				ident.append(sizeof(char), ch);
				ch = getchar();
			}
			if (!match('"'))
			{
				//在字符串内出现了非法字符
				error("There is an illegal character in the string");
				ident.clear();
				while (!match('"'))
				{
					ch = getchar();
					if (ch == EOF)
					{
						error("The Quotes don't match");
						return EOF;
					}
				}
			}
			ident.erase(--(ident.end()));			//去掉末尾的双引号
			return STRING;
		}
		else if (ch == EOF)
		{
			return EOF;
		}
		else 
		{
			//其他符号
			ident.clear();
			ident.append(sizeof(char), ch);
			res = keywordTable.find(ident);
			if (res != keywordTable.end() && res->second != 0)
			{
				//找到当前符号
				print("Sign", "Name", ident);
				ch = getchar();
				return res->second;
			}
			//当前符号为不可识别的符号
			//跳到下一个标识符或者数字开始的位置
			while (!isalnum(ch) && ch != EOF && keywordTable[std::string(1,ch)] == 0)
			{
				ch = getchar();
				ident.append(sizeof(char), ch);
			}
			ident.erase(--(ident.end()));			//去掉下一个标识符的开始字符
			if (ch == EOF)
			{
				return EOF;
			}
			return NUL;
		}
	}


}