Lex program to search a word in a file
Problem: Write a Lex program to search a word in a file.
Explanation:
FLEX (Fast Lexical Analyzer Generator) is a tool/computer program for generating lexical analyzers (scanners or lexers) written by Vern Paxson in C around 1987. Lex reads an input stream specifying the lexical analyzer and outputs source code implementing the lexer in the C programming language. The function yylex() is the main flex function which runs the Rule Section.
Examples:
Input: welcome to geeksforgeeks Output: welcome FOUND for NOT FOUND geeksforgeeks FOUND
Approach:
To search a word, I have stored words in file named “input.txt” and used lex to receive words from keyboard. On receiving each word, I check it with the words in the file. If the word is found, the program prints “FOUND” else “NOT FOUND”.
Input File: input.txt (Input File used in this program)
Below is the implementation of program:
/* Lex program to search a word in a file */ %{ /* Definition section */#include<string.h>void check(char *);%} /* Rule Section */%%[a-zA-Z]+ check(yytext);%% // driver codeint main(){ // The function that starts the analysis yylex(); return 0;}void check(char *str){ /* fp as pointer of File type */ FILE *fp; char temp[30]; /* fp points to the file input.txt and opens it in read mode */ fp=fopen("input.txt", "r"); while((fscanf(fp, "%s", temp))!=EOF) { if(!(strcmp(temp, str))) { printf("FOUND\n"); return; } } printf("NOT FOUND\n"); return;} |
Output:
