编译原理语法分析c语言代码
时间: 2023-12-15 08:33:24 浏览: 172
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:
```c
#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:
```python
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)
```
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