用c++写一个词法分析器

好的，下面是一个简单的 C++ 词法分析器示例：

#include <iostream>
#include <fstream>
#include <string>
#include <cctype>

using namespace std;

string keywords[32] = { "auto", "break", "case", "char", "const", "continue", "default",
                        "do", "double", "else", "enum", "extern", "float", "for", "goto",
                        "if", "int", "long", "register", "return", "short", "signed", "sizeof",
                        "static", "struct", "switch", "typedef", "union", "unsigned", "void",
                        "volatile", "while" };

bool isKeyword(string word)
{
    for (int i = 0; i < 32; i++)
    {
        if (keywords[i] == word)
            return true;
    }
    return false;
}

bool isOperator(char ch)
{
    char operators[] = "+-*/%=";
    for (int i = 0; i < 6; i++)
    {
        if (ch == operators[i])
            return true;
    }
    return false;
}

bool isDelimiter(char ch)
{
    char delimiters[] = "(){}[],.:;?";
    for (int i = 0; i < 10; i++)
    {
        if (ch == delimiters[i])
            return true;
    }
    return false;
}

int main()
{
    string input;
    cout << "Enter filename: ";
    getline(cin, input);

    ifstream file;
    file.open(input);
    if (!file)
    {
        cout << "Unable to open file!";
        exit(1);
    }

    char ch;
    string word;
    int line = 1;

    while (file >> noskipws >> ch)
    {
        if (ch == '\n')
            line++;

        if (isDelimiter(ch))
        {
            if (word.length() != 0)
            {
                if (isKeyword(word))
                    cout << word << " is a keyword" << endl;
                else
                    cout << word << " is an identifier" << endl;
            }
            cout << ch << " is a delimiter" << endl;
            word = "";
        }
        else if (isOperator(ch))
        {
            if (word.length() != 0)
            {
                if (isKeyword(word))
                    cout << word << " is a keyword" << endl;
                else
                    cout << word << " is an identifier" << endl;
            }
            cout << ch << " is an operator" << endl;
            word = "";
        }
        else if (isspace(ch))
        {
            if (ch == '\n')
                line++;
            if (word.length() != 0)
            {
                if (isKeyword(word))
                    cout << word << " is a keyword" << endl;
                else
                    cout << word << " is an identifier" << endl;
                word = "";
            }
        }
        else
        {
            word += ch;
        }
    }

    file.close();
    return 0;
}

这个词法分析器可以读取一个文件，将其分解为标识符、关键字、操作符和分隔符，并输出它们的类型。