编译原理 词法分析程序

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

#define KEYWORD_NUM 9

//二元组, 用于储存读入的单词
typedef struct 
{
	int code;				//单词识别码
	char value[20];			//单词自身值
} Tuple;

//关键字
const char keyword[KEYWORD_NUM][20] = { "if", "else", "int", "for", "while", "do", "return", "break", "continue" };

//判断读入的字符串是否为字符串
bool is_keyword(char* str);
//读入一个字符串
void read_string();
//读入一个数字
void read_digit();
//读入一个运算符
void read_operator();
//读入一个界符
void read_delimiter();

char c;				//指向下一个要读入的字符
FILE* fp;			//词法分析器要读入的字符串， 储存在一个文件中

Tuple tuples[100];		//储存产生的二元式
int num = 0;

int main()
{
	char filename[20];
	printf("Input Source Code Filename: ");
	scanf("%s", filename);
	fp = fopen(filename, "r");
	if (fp == NULL)
	{
		printf("Open File Error\n");
		exit(0);
	}

	while (!feof(fp))
	{
		c = fgetc(fp);
		//字符串
		if (isalpha(c))
		{
			read_string();
		}
		//数字
		else if (isdigit(c))
		{
			read_digit();	
		}
		//运算符
		else if (c == '>' || c == '<' || c == '=' || c == '!'
		 || c == '+' || c == '-' || c == '*' || c == '/')
		{
			read_operator();
		}
		//界符
		else if (c == ',' || c == '(' || c == ')' || c == '}' || c == '{')
		{
			read_delimiter();	
		}
	}

	for (int i = 0; i < num; i++)
	{
		printf("< %d, %s >\n", tuples[i].code, tuples[i].value);
	}
	fclose(fp);

	//把产生的中间二元式写入文件
	fp = fopen("middle_code.txt", "w");
	for (int i = 0; i < num; i++)
	{
		fprintf(fp, "<%d, %s>\n", tuples[i].code, tuples[i].value);
	}
	fclose(fp);

	return 0;
}

void read_delimiter()
{
	int cursor = 0;
	char buffer[20];

	buffer[cursor++] = c;
	buffer[cursor] = '\0';

	tuples[num].code = 5;
	strcpy((char*)tuples[num++].value, buffer);	
}

void read_digit()
{
	int cursor = 0;
	char buffer[20];

	buffer[cursor++] = c;
	c = fgetc(fp);
	//如果是数字， 则继续读入
	while (isdigit(c))
	{
		buffer[cursor++] = c;
		c = fgetc(fp);
	}
	buffer[cursor] = '\0';
	//多读了一个字符， 向后退还一个字符

	fseek(fp, -1, SEEK_CUR);

	tuples[num].code = 3;
	strcpy((char*)tuples[num++].value, buffer);
}

void read_operator()
{
	int cursor = 0;
	char buffer[20];

	buffer[cursor++] = c;
	c = fgetc(fp);
	//判断运算符是否为>=, <= ...
	if (c == '=')
	{
		buffer[cursor++] = c;
	}
	else
	{
		//多读了一个字符， 向后退还一个字符
		fseek(fp, -1, SEEK_CUR);
	}
	buffer[cursor] = '\0';

	tuples[num].code = 4;
	strcpy((char*)tuples[num++].value, buffer);
}

void read_string()
{
	int cursor = 0;
	char buffer[20];

	buffer[cursor++] = c;
	c = fgetc(fp);
	//如果是字符或数字， 则继续读入
	while (isalpha(c) || isdigit(c))
	{
		buffer[cursor++] = c;
		c = fgetc(fp);
	}
	buffer[cursor] = '\0';

	//多读了一个字符， 向后退回一个字符
	fseek(fp, -1, SEEK_CUR);

	//判读是关键字， 还是标识符	
	if (is_keyword(buffer))
	{
		tuples[num].code = 1;
		strcpy((char*)tuples[num++].value, buffer);
	}
	else
	{
		tuples[num].code = 2;
		strcpy((char*)tuples[num++].value, buffer);
	}
}

bool is_keyword(char* str)
{
	for (int i = 0; i < KEYWORD_NUM; i++)
	{
		if (strcmp(keyword[i], str) == 0)
		{
			return true;
		}
	}

	return false;

}