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File Handling in C

 what is file

File is a data structure ( sometimes also called as data types ) that can be use to store any data in it permanently .

In programming a file is handle using some file pointer of type ' File ' ( which is a data structure define as files in standard library ).

To use any file for reading , writing and for any other purpose usually following steps perform in sequence :-

1) Create a Pointer to the file :-      File *fp;

2) Open the file to work with : -
                                                           To open a file the standard function name ' fopen() ' is used as follow.
fp=fopen( " File_name ", " mode ");

if the file is successfully open it's pointer is return otherwise NULL is return . 
There are usually six mode that can be use :-

1) Read mode  ( ' r ' ): -   If file is unable to open then it return NULL.

2) Write mode (' w '):-  If specifies file is not exiting it creates a new file with that name.
3) Append mode (' a '):-  If we want to add contain after the last written contain then append mode is use . If the specified name file is not found it creates a new file with that file name.
4) r+ mode:- Opens a text file for both reading and writing.
5) w+ mode: -Opens a text file for both reading and writing. It first truncates the file to zero length if it exists, otherwise creates a file if it does not exist.
6) a+ mode :- Opens a text file for both reading and writing. It creates the file if it does not exist. The reading will start from the beginning but writing can only be appended.

Example:-  WAP to copy the context of one file to the another file 
int main()
FILE *fp1,*fp2;
char ch;
fp1= fopen("input.txt", "r");
fp2= fopen("ouput.txt", "w");
if(fp1==NULL || fp2==NULL)
//logic to copy
return 0;

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