词法分析器（纯c语言）

article/2025/11/1 10:15:36

一、原文章：词法分析器（分析C语言）

二、该词法分析器种别码表

三、词法分析器实现思路描述：

1.首先用一个数组来存储txt文本中非空白字符，并将存储字符的个数记录下来。

2.用scan()函数扫描数组中的字符，用index来定位当前扫描到的字符位置。

3.判断当前字符是哪种类型:

(1)若是字母，则有可能是关键字或标识符，需继续看下一个字符。若是关键字，再判断具体是哪个种别码；若是标识符，种别码为0。

(2)若是数字，是常量，种别码为24。

(3)若是运算符或界符,则需继续看下一个字符(因为可能是<=、>=、==、!=),再判断具体是哪个种别码。

(4)若不是以上三种，则输出。

二、用C语言改写并优化：

#pragma warning(disable:4996)
#include <stdio.h>
#include <ctype.h>
#include <string.h>
#include <stdlib.h>const int MAXN = 1000;
const int MINN = 20;bool isKey(char* s)  //是否是关键字
{const char* letter[6] = { "main","int","if","else","while","do" };for (int i = 0; i < 6; i++){if (strcmp(s, letter[i]) == 0)return true;}return false;
}
bool isOpebounder(char s) //是否是界符或运算符
{const char* str = "><=!(){},;+-*/";if (memchr(str, s, strlen(str)) != NULL)return true;elsereturn false;
}
int kindofKey(char* str) //判断哪种关键字 并返回其种别码
{const char* key[6] = { "main","int","if","else","while","do" };const int arr[6] = { 1,2,3,4,5,6 };for (int i = 0; i < 6; i++){if (strcmp(str, key[i]) == 0)return arr[i];}
}
int kindofOpebounder(char* str) //判断哪种运算符和界符 并返回其种别码
{const char* opebounder[17] = { "<",">","!=",">=","<=","==",",",";","(",")","{","}","+","-","*","/","=" };const int arr[MINN] = { 7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23 };for (int i = 0; i < 17; i++){if (strcmp(str, opebounder[i]) == 0)return arr[i];}
}
char* firstLetter(char* s) //首字符为字母
{int size = 0;//单词长度char str[MINN] = ""; //单词char c;    //存储当前字符的下一个 方便作为实参以识别类型str[size++] = *s; //保存当前字符并增加长度while (c = *(s + size)){if (islower(c) || isdigit(c)) //下一个字符是字母或数字则保存在str中str[size++] = c;elsebreak;if (isKey(str)) //如果单词恰好是关键字 则终止循环break;}return str;
}char* firstNumber(char* s) //首字符为数字
{int size = 0;char str[MINN] = "";char c;str[size++] = *s;while (c = *(s + size)){if (isdigit(c)) //下一个字符是字母或数字则保存在str中str[size++] = c;elsebreak;}return str;}
char* firstOpebounder(char* s) //首字符为运算符和界符
{char arr[MINN] = ">=<!";char str[MINN] = "";char c = *(s + 1);str[0] = *s;if (memchr(arr, *s, strlen(arr)) != NULL){if (c == '=')str[1] = '=';}return str;
}
int Type(char* s) //判断单词的首字母为哪种类型
{if (islower(*s))return 1;else if (isdigit(*s))return 2;else if (isOpebounder(*s))return 3;elsereturn 4;
}
void scan(char* s, int n)
{for (int index = 0; index < n;index++){char str[MINN] = ""; //存储单词switch (Type(s + index)){case 1:{//首字符为字母 可能是关键字或标识符 接下来持续读取字母形成单词strcpy(str, firstLetter(s + index));if (isKey(str))printf("(%s,%d)\n", str, kindofKey(str));elseprintf("(%s,0)\n", str);index += (strlen(str) - 1);break;}case 2:{//首字符为数字，只能是常量strcpy(str, firstNumber(s+index));printf("(%s,24)\n", str);index += (strlen(str) - 1);break;}case 3:{//首字符为运算符和界符strcpy(str, firstOpebounder(s+index));printf("(%s,%d)\n", str, kindofOpebounder(str));index += (strlen(str) - 1);break;}default:{//其他printf("(%c,error)\n", *(s+index));}}}
}int main(void)
{char letter[MAXN] = ""; //存储要扫描的字符int size = 0;  //字符的个数//与s.txt文件连接并读取里面的内容FILE* fp;fp = fopen("s.txt", "r");char ch = getc(fp);while (ch != EOF){if (ch != ' '&&ch !='\n')  //保存非空白字符{letter[size] = ch;size++;}ch = getc(fp);}fclose(fp);//开始扫，并将结果以二元的形式打印在屏幕上scan(letter, size);return 0;
}