c语言词法分析器_C和C ++中的词法分析器

刺骨的言语ヽ痛彻心扉 2022-12-07 14:00 156阅读 0赞

![391bfda1ef66d8418be2ee2d73a96f0d.png][]

c语言词法分析器

Here you will get program to implement lexical analyzer in C and C++.

在这里，您将获得在C和C ++中实现词法分析器的程序。

Compiler is responsible for converting high level language in machine language. There are several phases involved in this and lexical analysis is the first phase.

编译器负责将高级语言转换为机器语言。 此过程涉及多个阶段，词汇分析是第一阶段。

Lexical analyzer reads the characters from source code and convert it into tokens.

词法分析器从源代码中读取字符并将其转换为令牌。

![Lexical Analyzer in C and C++][Lexical Analyzer in C and C]

Different tokens or lexemes are:

不同的标记或词素是：

*  Keywords
    
    关键词
 *  Identifiers
    
    身份标识
 *  Operators
    
    经营者
 *  Constants
    
    常数

Take below example.

请看下面的例子。

**c = a + b;**

After lexical analysis a symbol table is generated as given below.

经过词法分析后，将生成一个符号表，如下所示。

<table> 
 <tbody> 
  <tr> 
   <td><strong>Token</strong></td> 
   <td><strong>Type</strong></td> 
  </tr> 
  <tr> 
   <td>c</td> 
   <td>identifier</td> 
  </tr> 
  <tr> 
   <td>=</td> 
   <td>operator</td> 
  </tr> 
  <tr> 
   <td>a</td> 
   <td>identifier</td> 
  </tr> 
  <tr> 
   <td>+</td> 
   <td>operator</td> 
  </tr> 
  <tr> 
   <td>b</td> 
   <td>identifier</td> 
  </tr> 
  <tr> 
   <td>;</td> 
   <td>separator</td> 
  </tr> 
 </tbody> 
</table>

Now below I have given implementation of very simple lexical analyzer which reads source code from file and then generate tokens.

现在在下面，我给出了非常简单的词法分析器的实现，该词法分析器从文件中读取源代码，然后生成令牌。

## 用C语言编写词法分析器的程序 **(**Program for Lexical Analyzer in C**)** ##

#include<stdio.h>
    #include<stdlib.h>
    #include<string.h>
    #include<ctype.h>
     
    int isKeyword(char buffer[]){
    	char keywords[32][10] = {"auto","break","case","char","const","continue","default",
    							"do","double","else","enum","extern","float","for","goto",
    							"if","int","long","register","return","short","signed",
    							"sizeof","static","struct","switch","typedef","union",
    							"unsigned","void","volatile","while"};
    	int i, flag = 0;
    	
    	for(i = 0; i < 32; ++i){
    		if(strcmp(keywords[i], buffer) == 0){
    			flag = 1;
    			break;
    		}
    	}
    	
    	return flag;
    }
     
    int main(){
    	char ch, buffer[15], operators[] = "+-*/%=";
    	FILE *fp;
    	int i,j=0;
    	
    	fp = fopen("program.txt","r");
    	
    	if(fp == NULL){
    		printf("error while opening the file\n");
    		exit(0);
    	}
    	
    	while((ch = fgetc(fp)) != EOF){
       		for(i = 0; i < 6; ++i){
       			if(ch == operators[i])
       				printf("%c is operator\n", ch);
       		}
       		
       		if(isalnum(ch)){
       			buffer[j++] = ch;
       		}
       		else if((ch == ' ' || ch == '\n') && (j != 0)){
       				buffer[j] = '\0';
       				j = 0;
       				   				
       				if(isKeyword(buffer) == 1)
       					printf("%s is keyword\n", buffer);
       				else
       					printf("%s is indentifier\n", buffer);
       		}
       		
    	}
    	
    	fclose(fp);
    	
    	return 0;
    }

## C ++中的词法分析器程序 **(**Program for Lexical Analyzer in C++**)** ##

#include<iostream>
    #include<fstream>
    #include<stdlib.h>
    #include<string.h>
    #include<ctype.h>
     
    using namespace std;
     
    int isKeyword(char buffer[]){
    	char keywords[32][10] = {"auto","break","case","char","const","continue","default",
    							"do","double","else","enum","extern","float","for","goto",
    							"if","int","long","register","return","short","signed",
    							"sizeof","static","struct","switch","typedef","union",
    							"unsigned","void","volatile","while"};
    	int i, flag = 0;
    	
    	for(i = 0; i < 32; ++i){
    		if(strcmp(keywords[i], buffer) == 0){
    			flag = 1;
    			break;
    		}
    	}
    	
    	return flag;
    }
     
    int main(){
    	char ch, buffer[15], operators[] = "+-*/%=";
    	ifstream fin("program.txt");
    	int i,j=0;
    	
    	if(!fin.is_open()){
    		cout<<"error while opening the file\n";
    		exit(0);
    	}
    	
    	while(!fin.eof()){
       		ch = fin.get();
       		
    		for(i = 0; i < 6; ++i){
       			if(ch == operators[i])
       				cout<<ch<<" is operator\n";
       		}
       		
       		if(isalnum(ch)){
       			buffer[j++] = ch;
       		}
       		else if((ch == ' ' || ch == '\n') && (j != 0)){
       				buffer[j] = '\0';
       				j = 0;
       				   				
       				if(isKeyword(buffer) == 1)
       					cout<<buffer<<" is keyword\n";
       				else
       					cout<<buffer<<" is indentifier\n";
       		}
       		
    	}
    	
    	fin.close();
    	
    	return 0;
    }

**Output**

**输出量**

![Lexical Analyzer in C and C++][Lexical Analyzer in C and C 1]

The source code present in file is shown in above image.

文件中存在的源代码如上图所示。

Comment below if you have any queries regarding above program for lexical analyzer in C and C++.

如果对C和C ++中的词法分析器的上述程序有任何疑问，请在下面评论。

> 翻译自: [https://www.thecrazyprogrammer.com/2017/02/lexical-analyzer-in-c.html][https_www.thecrazyprogrammer.com_2017_02_lexical-analyzer-in-c.html]

c语言词法分析器

[391bfda1ef66d8418be2ee2d73a96f0d.png]: /images/20221123/9c37bd192bfa46798a6aed648f65572d.png
[Lexical Analyzer in C and C]: /images/20221123/cdcade264f63491b9eb88906a741931f.png
[Lexical Analyzer in C and C 1]: /images/20221123/dd52bf8f247642e1a43c9dc35570ed35.png
[https_www.thecrazyprogrammer.com_2017_02_lexical-analyzer-in-c.html]: https://www.thecrazyprogrammer.com/2017/02/lexical-analyzer-in-c.html