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In our last article, we have explained how to read an existing file on the disk. In this tutorial, we are going to explain how to write to a file on disk. For this, the C language provides us a structure called FILE, which is defined in the header file <conio.h>. The FILE structure allows us to create, read, write/modify the file on disk.

The FILE structure provides us a function named fopen(), using which we could provide location of the file stored on the disk and in return(if the file is found), the fopen() function open the file and gives us a pointer which is pointed at the position where the first character has to be written in the file.

• Syntax of fopen() function




FILE *fopen(const char *filename, const char *mode)


where filename is the name of the file being searched and mode defines the mode in which the file is opened. As, we have to open a file for writing, hence this mode will take a string value "w".



File Mode	Description
"w"	Searches for the file and if the file is found, its content are overwritten. If file is not found, a new file is created. Allows you to write to the file.


Using this mode, if this file does not exist on the disk then it will be created and if it already exists then its content will be overwritten. In both cases, this function returns the pointer to the first character position in the file.






• Writing a file by taking input from a char[] array


Let us see a write to a file on disk by taking input from an already initialized char[] array, This file will be created in the current directory(the same directory where we are going to store the upcoming C program.).



#include<stdio.h>
#include<conio.h>

int main()
{

char str[100] = "Hello, how are you going? Have a pleasant day ahead!";


/* this will create the file in the directory where this C program file is stored */
FILE *fw = fopen("File2.txt", "w");

char ch;

int i=0;

while(str[i]!='\0')
{
	fputc(str[i], fw);
	i++;
}
fclose(fw);

return 0;
}




Output


Executing this program will create a file named File2.txt in the current directory, with its content similar to the content of char[] array str, such as -



Hello, how are you going? Have a pleasant day ahead!






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• Writing a file by taking input from user at console


Let us see a write to a file on disk by taking input from the user at the console, This file will be created in the current directory(the same directory where we are going to store the upcoming C program.).



#include<stdio.h>
#include<conio.h>

int main()
{
char str[200];

printf("Enter the content you want to write to a file : \n");
gets(str);


/* this will create the file in the directory where this C program file is stored */
FILE *fw = fopen("File3.txt", "w");

char ch;

int i=0;

while(str[i]!='\0')
{
	fputc(str[i], fw);
	i++;
}
fclose(fw);

return 0;
}




Output




Enter the content you want to write to a file :
Always look at the bright side of life. Keep smiling and never give up!



Executing this program will create a file named File3.txt in the current directory, with its content taken from the input typed by the user at the console such as -



Always look at the bright side of life. Keep smiling and never give up!



In the next tutorial, we are going to modify the content of an existing file.






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