词法分析器 C++代码

以下是一个简单的词法分析器的 C 代码示例：

#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>

#define MAX_TOKEN_LEN 100

typedef enum {
    INT,
    FLOAT,
    ID,
    ADD_OP,
    SUB_OP,
    MULT_OP,
    DIV_OP,
    ASSIGN_OP,
    LEFT_PAREN,
    RIGHT_PAREN,
    SEMICOLON
} token_type;

typedef struct {
    token_type type;
    char value[MAX_TOKEN_LEN];
} token;

token current_token;

void get_token() {
    int i = 0;
    char ch = getchar();

    while (isspace(ch)) {
        ch = getchar();
    }

    if (isdigit(ch)) {
        while (isdigit(ch)) {
            current_token.value[i++] = ch;
            ch = getchar();
        }
        if (ch == '.') {
            current_token.type = FLOAT;
            current_token.value[i++] = ch;
            ch = getchar();
            while (isdigit(ch)) {
                current_token.value[i++] = ch;
                ch = getchar();
            }
        }
        else {
            current_token.type = INT;
        }
        ungetc(ch, stdin);
    }
    else if (isalpha(ch)) {
        while (isalnum(ch)) {
            current_token.value[i++] = ch;
            ch = getchar();
        }
        ungetc(ch, stdin);
        current_token.type = ID;
    }
    else if (ch == '+') {
        current_token.type = ADD_OP;
        current_token.value[i++] = ch;
    }
    else if (ch == '-') {
        current_token.type = SUB_OP;
        current_token.value[i++] = ch;
    }
    else if (ch == '*') {
        current_token.type = MULT_OP;
        current_token.value[i++] = ch;
    }
    else if (ch == '/') {
        current_token.type = DIV_OP;
        current_token.value[i++] = ch;
    }
    else if (ch == '=') {
        current_token.type = ASSIGN_OP;
        current_token.value[i++] = ch;
    }
    else if (ch == '(') {
        current_token.type = LEFT_PAREN;
        current_token.value[i++] = ch;
    }
    else if (ch == ')') {
        current_token.type = RIGHT_PAREN;
        current_token.value[i++] = ch;
    }
    else if (ch == ';') {
        current_token.type = SEMICOLON;
        current_token.value[i++] = ch;
    }
    else {
        current_token.type = -1;
        current_token.value[i++] = ch;
    }

    current_token.value[i] = '\0';
}

int main() {
    while (current_token.type != -1) {
        get_token();
        printf("Token Type: %d, Value: %s\n", current_token.type, current_token.value);
    }

    return 0;
}

该代码实现了一个简单的词法分析器，可以读取并识别输入的字符串中的基本单词类型，如整数、浮点数、标识符、运算符、括号和分号等，然后输出每个单词的类型和值。