词法分析器的超前搜索c++代码

下面是一个简单的词法分析器的超前搜索C++代码：

#include <iostream>
#include <string>

using namespace std;

enum TokenType {
    INTEGER,
    PLUS,
    MINUS,
    MUL,
    DIV,
    LPAREN,
    RPAREN,
    EOF_TYPE
};

class Token {
public:
    TokenType type;
    string value;

    Token(TokenType type, string value) {
        this->type = type;
        this->value = value;
    }
};

class Lexer {
public:
    string text;
    int pos;
    char current_char;

    Lexer(string text) {
        this->text = text;
        this->pos = 0;
        this->current_char = this->text[this->pos];
    }

    void error() {
        throw runtime_error("Invalid character");
    }

    void advance() {
        this->pos++;
        if (this->pos > this->text.length() - 1) {
            this->current_char = '\0';
        } else {
            this->current_char = this->text[this->pos];
        }
    }

    void skip_whitespace() {
        while (this->current_char != '\0' && isspace(this->current_char)) {
            this->advance();
        }
    }

    int integer() {
        string result = "";
        while (this->current_char != '\0' && isdigit(this->current_char)) {
            result += this->current_char;
            this->advance();
        }
        return stoi(result);
    }

    Token get_next_token() {
        while (this->current_char != '\0') {
            if (isspace(this->current_char)) {
                this->skip_whitespace();
                continue;
            }
            if (isdigit(this->current_char)) {
                return Token(INTEGER, to_string(this->integer()));
            }
            if (this->current_char == '+') {
                this->advance();
                return Token(PLUS, "+");
            }
            if (this->current_char == '-') {
                this->advance();
                return Token(MINUS, "-");
            }
            if (this->current_char == '*') {
                this->advance();
                return Token(MUL, "*");
            }
            if (this->current_char == '/') {
                this->advance();
                return Token(DIV, "/");
            }
            if (this->current_char == '(') {
                this->advance();
                return Token(LPAREN, "(");
            }
            if (this->current_char == ')') {
                this->advance();
                return Token(RPAREN, ")");
            }
            this->error();
        }
        return Token(EOF_TYPE, "");
    }
};

int main() {
    while (true) {
        string text;
        cout << "calc> ";
        getline(cin, text);
        Lexer lexer(text);
        Token token = lexer.get_next_token();
        while (token.type != EOF_TYPE) {
            cout << "(" << token.type << ", " << token.value << ")" << endl;
            token = lexer.get_next_token();
        }
        cout << "(" << token.type << ", " << token.value << ")" << endl;
    }
    return 0;
}

这个代码实现了一个简单的词法分析器，它可以读取用户输入的算术表达式并将其转换为一系列令牌(Token)。在这个代码中，我们使用了一个枚举类型(TokenType)来表示令牌的类型，使用了一个Token类来表示单个令牌，并使用了一个Lexer类来实现超前搜索算法来逐个获取令牌。