Advertisement

---

Top

< Prev

Next >

In our last article, we have explained how to write to a file on the disk. In this tutorial, we are going to explain how to append data to an existing 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 either the first character position or the last character position in the file, depending on the mode in which we open this file. Let's read the file mode to use to append new data to 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 to append new data, hence this mode will take a string value "a".



File Mode	Description
"a"	Searches for the file and if the file is found, the pointer to its last character is returned. Allows you to append new data to the file. If file is not found, a new file is created.


Using this mode, if this file does not exist on the disk then it will be created and if it already exists this function returns the pointer to the last character position in the file to append new data at the end of file.






• Appending data a file by taking input from a char[] array


Let's say that we already have an existing file on disk, named File1.txt, with content :



Greetings! Hope you are doing well. 


Now let's try to write and append data to this file by taking input from an already initialized char[] array, This file will be searched 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] = "Best wishes for all your endeavours!";
char ch;

/* This will append the data of char array the file named File1.txt  */
FILE *fa = fopen("File1.txt", "a");

/* If the searched file is not found, the program exits */
if(fa==NULL)
{
        printf("can not open target file\n");
        exit(1);
}

int i=0;

/* If the file is found */
while(str[i]!='\0')
{
	fputc(str[i], fa);
	i++;
}
fclose(fa);

return 0;
}




Output


Executing this program will append the content of char[] to the end of a file named File2.txt in the current directory, with its content :



Greetings! Hope you are doing well. Best wishes for all your endeavours!






Advertisement






• Appending data a file by taking input from user at console


Let's say that we already have an existing file on disk, named File2.txt, with content :



Too much of work and no play made Jack a dull boy. 


Let us append data to a file on disk by taking input from the user at the console, This file will be searched 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 append to the file : \n");
gets(str);


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


/* If the searched file is not found, the program exits */
if(fa==NULL)
{
        printf("can not open target file\n");
        exit(1);
}

/* If the file is found */
char ch;

int i=0;

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

return 0;
}




Output




Enter the content you want to append to the file :
Jack must also enjoy his life.



Executing this program will append the data entered by the user at the console at the end of a file named File2.txt in the current directory. Let's see the content of this file



Too much of work and no play made Jack a dull boy. Jack must also enjoy his life.



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






Please share this article -







< Prev
Next >
< Reading a File
Append to a File >



Advertisement