编译原理实验（一）——词法分析-蒲公英云

编译原理实验（一）——词法分析

- - 实验要求
  - 参考程序
  - 运行截图

实验要求

输入为字符串（或待进行词法分析的源程序），输出为单词串，即由（单词，类别）所组成的二元组序列；

参考程序

#include <string>
#include <iostream>
#include <fstream>
#include <set>
using namespace std;
const int maxLineNum = 100;
set<string> key;             //关键字
char ch;                     //当前读取字符
int col, maxcol;             // col 读取当前行位置，当前行最大长度
ifstream readfile;           //文件输入流
char line[maxLineNum];       //读取文件一行
char identifier[maxLineNum]; //保留读取标识符或者关键字
void init();                 //进行初始化工作
int getsym();                //进行词法分析
int getch();                 //读取一个字符
int main()
{ 
    cout << "请输入要分析的文件名（请放在该程序同一目录）: ";
    string filename = "";
    cin>>filename;
    readfile.open(filename);
    if (readfile.is_open() == false)
    { 
        cout << "文件不存在";
        return 0;
    }
    init();
    col = maxcol = 0;
    ch = ' ';
    while (getsym())
        ;
    return 0;
}
void init()
{ 
    key.insert("const");
    key.insert("do");
    key.insert("while");
    key.insert("if");
    key.insert("else");
    key.insert("for");
    key.insert("int");
    key.insert("char");
    key.insert("return");
    key.insert("void");
    key.insert("read");
    key.insert("write");
}
int getch()
{ 
    if (col == maxcol)
    { 
        if (readfile.peek() == EOF)
        { 
            return -1;
        }
        maxcol = col = 0;
        ch = ' ';
        while (ch != '\n')
        { 
            if (readfile.peek() == EOF)
            { 
                line[maxcol] = 0;
                break;
            }
            readfile.get(ch);
            line[maxcol++] = ch;
        }
    }
    ch = line[col++];
    return 0;
}
int getsym()
{ 
    int i, j, k, num;
    while (ch == ' ' || ch == 10 || ch == 13 || ch == 9)
    { 
        if (getch() == -1)
            return 0;
    }
    if (isalpha(ch))
    { 
        k = 0;
        while (isalpha(ch) || isdigit(ch))
        { 
            identifier[k] = ch;
            k++;
            if (getch() == -1)
                return 0;
        }
        identifier[k] = 0;
        if (key.find(string(identifier)) == key.end())
        { 
            cout << "标识符 (3 , '" << identifier << "')\n";
        }
        else
        { 
            cout << "关键字 (1 , '" << identifier << "')\n";
        }
    }
    else
    { 
        if (isdigit(ch))
        { 
            k = num = 0;
            while (isdigit(ch))
            { 
                num = num * 10 + ch - '0';
                k++;
                if (getch() == -1)
                    return 0;
            }
            if(isalpha(ch)||ch=='_'){ 
                cout<<"非法标识符 (6,'"<<num<<ch<<"')\n";
            }else{ 
                cout << "整数 (2 , '" << num << "')\n";
            }
        }
        else
        { 
            if (ch == '<')
            { 
                if (getch() == -1)
                    return 0;
                if (ch == '=')
                { 
                    cout << "运算符 (4 , '<=')\n";
                    if (getch() == -1)
                        return 0;
                }
                else
                { 
                    cout << "运算符 (4 , '<')\n";
                }
            }
            else if (ch == '>')
            { 
                if (getch() == -1)
                    return 0;
                if (ch == '=')
                { 
                    cout << "运算符 (4 , '>=')\n";
                    if (getch() == -1)
                        return 0;
                }
                else
                { 
                    cout << "运算符 (4 , '>')\n";
                }
            }
            else
            { 
                if (ch == '+')
                { 
                    cout << "运算符 (4 , '+')\n";
                }
                else if (ch == '-')
                { 
                    cout << "运算符 (4 , '-')\n";
                }
                else if (ch == '*')
                { 
                    cout << "运算符 (4 , '*')\n";
                }
                else if (ch == '/')
                { 
                    cout << "运算符 (4 , '/')\n";
                }
                else if (ch == '=')
                { 
                    cout << "运算符 (4 , '=')\n";
                }
                else if (ch == '(')
                { 
                    cout << "运算符 (4 , '(')\n";
                }
                else if (ch == ')')
                { 
                    cout << "运算符 (4 , ')')\n";
                }
                else if (ch == '.')
                { 
                    cout << "运算符 (4 , '.')\n";
                }
                else if (ch == ',')
                { 
                    cout << "分界符 (5 , ',')\n";
                }
                else if (ch == ';')
                { 
                    cout << "分界符 (5 , ';')\n";
                }
                else if (ch == '{')
                { 
                    cout << "分界符 (5 , '{')\n";
                }
                else if (ch == '}')
                { 
                    cout << "分界符 (5 , '}')\n";
                }
                else
                { 
                    cout << ch << " error!请检查代码是否拼写正确！";
                    return 0;
                }
                if (getch() == -1)
                    return 0;
            }
        }
    }
    return 1;
}