编译原理语法分析c语言代码

编译原理中的语法分析是将代码转换为抽象语法树的过程。在C语言中，语法分析器通常使用自顶向下的递归下分析方法。以下是一个简单的C语言代码示和相应的语分析器实现：

设我们有以下C语言代码：

#include <stdio.h>

int main() {
    int a = 1;
    int b = 2;
    int c = a + b;
    printf("The sum of a and b is %d", c);
    return 0;
}

我们可以使用递归下降分析器来解析这段代码。下面是一个简单的实现：

import re

# 定义C语言的语法规则
# 这里只列出了一部分规则，实际上C语言的语法规则非常复杂
rules = {
    'program': ['INCLUDES main'],
    'INCLUDES': ['include <stdio.h>'],
    'main': ['INT MAIN LPAREN RPAREN LBRACE declarations statements RETURN NUMBER SEMI RBRACE'],
    'declarations': ['INT ID SEMI declarations', ''],
    'statements': ['statement statements', ''],
    'statement': ['assignment_statement', 'print_statement'],
    'assignment_statement': ['INT ID EQUALS NUMBER SEMI'],
    'print_statement': ['PRINTF LPAREN STRING COMMA ID RPAREN SEMI']
}

# 定义一个Token类来表示代码中的单词
class Token:
    def __init__(self, type, value):
        self.type = type
        self.value = value

    def __str__(self):
        return 'Token({type}, {value})'.format(
            type=self.type,
            value=repr(self.value)
        )

# 定义一个Lexer类来将代码转换为Token序列
class Lexer:
    def __init__(self, text):
        self.text = text
        self.pos = 0
        self.current_char = self.text[self.pos]

    def error(self):
        raise Exception('Invalid character')

    def advance(self):
        self.pos += 1
        if self.pos > len(self.text) - 1:
            self.current_char = None
        else:
            self.current_char = self.text[self.pos]
    def skip_whitespace(self):
        while self.current_char is not None and self.current_char.isspace():
            self.advance()

    def integer(self):
        result = ''
        while self.current_char is not None and self.current_char.isdigit():
            result += self.current_char
            self.advance()
        return int(result)

    def get_next_token(self):
        while self.current_char is not None:
            if self.current_char.isspace():
                self.skip_whitespace()
                continue
            if self.current_char.isdigit():
                return Token('NUMBER', self.integer())
            if self.current_char == '+':
                self.advance()
                return Token('PLUS', '+')
            if self.current_char == '-':
                self.advance()
                return Token('MINUS', '-')
            if self.current_char == '*':
                self.advance()
                return Token('MULTIPLY', '*')
            if self.current_char == '/':
                self.advance()
                return Token('DIVIDE', '/')
            if self.current_char == '(':
                self.advance()
                return Token('LPAREN', '(')
            if self.current_char == ')':
                self.advance()
                return Token('RPAREN', ')')
            if self.current_char == '{':
                self.advance()
                return Token('LBRACE', '{')
            if self.current_char == '}':
                self.advance()
                return Token('RBRACE', '}')
            if self.current_char == ';':
                self.advance()
                return Token('SEMI', ';')
            if self.current_char == '=':
                self.advance()
                return Token('EQUALS', '=')
            if self.current_char == ',':
                self.advance()
                return Token('COMMA', ',')
            if self.current_char == '"':
                self.advance()
                string = ''
                while self.current_char is not None and self.current_char != '"':
                    string += self.current_char
                    self.advance()
                if self.current_char == '"':
                    self.advance()
                    return Token('STRING', string)
                else:
                    self.error()
            if self.current_char.isalpha():
                word = ''
                while self.current_char is not None and (self.current_char.isalpha() or self.current_char.isdigit() or self.current_char == '_'):
                    word += self.current_char
                    self.advance()
                if word.upper() == 'INT':
                    return Token('INT', 'int')
                if word.upper() == 'PRINTF':
                    return Token('PRINTF', 'printf')
                if word.upper() == 'RETURN':
                    return Token('RETURN', 'return')
                if word.upper() == 'MAIN':
                    return Token('MAIN', 'main')
                if word.upper() == 'INCLUDE':
                    return Token('INCLUDE', 'include')
                if word.upper() == 'STDIO':
                    return Token('STDIO', 'stdio')
                return Token('ID', word)
            self.error()
        return Token('EOF', None)

# 定义一个Parser类来将Token序列转换为抽象语法树
class Parser:
    def __init__(self, lexer):
        self.lexer = lexer
        self.current_token = self.lexer.get_next_token()

    def error(self):
        raise Exception('Invalid syntax')

    def eat(self, token_type):
        if self.current_token.type == token_type:
            self.current_token = self.lexer.get_next_token()
        else:
            self.error()

    def program(self):
        includes_node = self.includes()
        main_node = self.main()
        return (includes_node, main_node)

    def includes(self):
        self.eat('INCLUDE')
        self.eat('STDIO')
        self.eat('.')
        self.eat('H')
        return ('INCLUDES',)

    def main(self):
        self.eat('INT')
        self.eat('MAIN')
        self.eat('LPAREN')
        self.eat('RPAREN')
        self.eat('LBRACE')
        declarations_node = self.declarations()
        statements_node = self.statements()
        self.eat('RETURN')
        number_node = self.number()
        self.eat('SEMI')
        self.eat('RBRACE')
        return ('MAIN', declarations_node, statements_node, number_node)

    def declarations(self):
        declarations_node = ('DECLARATIONS',)
        while self.current_token.type == 'INT':
            declaration_node = self.declaration()
            declarations_node += (declaration_node,)
        return declarations_node

    def declaration(self):
        self.eat('INT')
        id_node = self.variable()
        self.eat('SEMI')
        return ('DECLARATION', id_node)

    def variable(self):
        token = self.current_token
        self.eat('ID')
        return ('VAR', token.value)

    def statements(self):
        statements_node = ('STATEMENTS',)
        while self.current_token.type in ['ID', 'PRINTF']:
            statement_node = self.statement()
            statements_node += (statement_node,)
        return statements_node

    def statement(self):
        if self.current_token.type == 'ID':
            assignment_statement_node = self.assignment_statement()
            return assignment_statement_node
        elif self.current_token.type == 'PRINTF':
            print_statement_node = self.print_statement()
            return print_statement_node

    def assignment_statement(self):
        id_node = self.variable()
        self.eat('EQUALS')
        number_node = self.number()
        self.eat('SEMI')
        return ('ASSIGNMENT', id_node, number_node)

    def print_statement(self):
        self.eat('PRINTF')
        self.eat('LPAREN')
        string_node = self.string()
        self.eat('COMMA')
        id_node = self.variable()
        self.eat('RPAREN')
        self.eat('SEMI')
        return ('PRINT', string_node, id_node)

    def string(self):
        token = self.current_token
        self.eat('STRING')
        return ('STRING', token.value)

    def number(self):
        token = self.current_token
        self.eat('NUMBER')
        return ('NUMBER', token.value)

    def parse(self):
        return self.program()

# 将代码转换为Token序列
lexer = Lexer(text)
tokens = []
while True:
    token = lexer.get_next_token()
    if token.type == 'EOF':
        break
    tokens.append(token)

# 将Token序列转换为抽象语法树
parser = Parser(Lexer(text))
ast = parser.parse()
print(ast)