Write a well-commented C program that accepts the name of a file and a \"field-n

Question

Write a well-commented C program that accepts the name of a file and a "field-number" from the user, and then reads that file and for each line in that file prints on the terminal word at position "field-number" and also writes the word into an output file. For example, if the input file as the following lines:

C is a programming language.

lex produces a lexical analyser

cc is a compiler

and if the field-number specified is 4, then the output of the program is:

programming

lexical

(NULL)
compiler

Explanation / Answer

The required code for completing the task is given below. Read the specified input file line by line, tokenized the words and found the word at target field number, displayed it and saved to a file. Comments are included in every statements.Thanks.

//code.c

#include<stdio.h>

#include <string.h>

int main(){

                char filename[50];//for storing input file name

                char outputfilename[]="result.txt"; //output file name

                int required_field; //for storing required field number

                FILE *fp,*ofp;//defining file pointers for input and output files

                //reading input file

                printf("Enter file name: ");

                scanf("%s",&filename);

                fp=fopen(filename,"r");//reading input file in read mode

                //making sure input file exist and is readable

                if(!fp){

                                printf("File not found! ");

                                return 0;

                }

                //getting field number

                printf("Enter field number: ");

                scanf("%d",&required_field);

                //opening output file for writing

                ofp=fopen(outputfilename,"w");

                char line[250];//buffer for storing each line of text

                char *word_token; //used for tokenizing each line

                int field_number=0; //used for iterating through each word (field)

                //looping through each line

                while (fgets(line, sizeof(line), fp)) {

                                //tokenizing the line (splitting it by delimeters - white spaces

                                // or next line character )

                                word_token=strtok (line," ");

                                field_number=1;

                                //looping through each tokens until target field

                                //or until word token becomes null

                                while(field_number!=required_field && word_token!=NULL){

                                                word_token = strtok (NULL, " ");//getting next token

                                field_number++;

                                }

                                if(word_token==NULL){

                                                //null value, displaying and saving to file

                                                printf("(NULL) ");

                                                fprintf(ofp,"(NULL) ");

                                }else{

                                                //field value at given position, displaying and saving to file

                                                printf ("%s ",word_token);

                                                fprintf(ofp,"%s ",word_token);

                                }

    }

    fclose(fp);

    fclose(ofp);

}

//output

Enter file name: students.txt

Enter field number: 2

Alice

Bob

Dave

Eric

Chris

Zaid

Emily

//students.txt (used input file)

123 Alice Al 3.4

587 Bob bobby 3.8

228 Dave D 3.1

321 Eric Erix 2.5

555 Chris christy 3.9

710 Zaid Z 3.2

124 Emily Clay 3.7

//results.txt(after running the program)

Alice

Bob

Dave

Eric

Chris

Zaid

Emily

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