How to do it…

The following are the steps to create a random file and enter a few lines of text in it. You can enter any number of lines as desired; simply type stop, followed by the Enter key, when you are done:

1. Define a structure consisting of a string member:

struct data{
    char str[ 255 ];
};

2. Open a random file in write-only mode and point to it with a file pointer:

fp = fopen (argv[1], "wb");

3. The program will terminate if the file cannot be opened in write-only mode:

if (fp == NULL) {
    perror ("An error occurred in creating the file\n");
    exit(1);
}

4. Enter the file contents when prompted and store it into the structure members:

printf("Enter file content:\n");
gets(line.str);

5. If the text entered is not stop, the structure containing the text is written into the file:

while(strcmp(line.str, "stop") !=0){
    fwrite( &line, sizeof(struct data), 1, fp );

6. Steps 4 and 5 are repeated until you enter stop.
7. When you enter stop, the file pointed at by the file pointer is closed to release the resources allocated to the file:

fclose(fp);

The createrandomfile.c program for creating a random file is as follows:

#include <string.h>
#include <stdio.h>
#include <stdlib.h>

struct data{  
    char str[ 255 ];  
};

void main (int argc, char* argv[])
{
    FILE *fp;
    struct data line;
    fp = fopen (argv[1], "wb");
    if (fp == NULL) {
        perror ("An error occurred in creating the file\n");            
        exit(1);
    }
    printf("Enter file content:\n");
    gets(line.str);
    while(strcmp(line.str, "stop") !=0){
        fwrite( &line, sizeof(struct data), 1, fp );
        gets(line.str);
    }
    fclose(fp);
}

Now, let's go behind the scenes to understand the code better.