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;

}