How to Open a File in C

if we want to store data in the secondary memory, we must specify certain things about the file, to the operating system. They include:

1.      Filename

2.      Data structure

3.      Purpose

Filename is a string of characters that make up a valid filename for the operating system. It may contain two parts, a primary name and an optional period with the extension. Examples are:

Input.data

store

student.c

Text.out

Data structure of a file is defined as FILE in the library of standard I/O function definitions. Therefore, all files should be declared as type FILE before they are used. FILE is a defined data type.

When we open a file, we must specify what we want to do with the file. For example, we may write data to the file or read the already existing data.

Following is the general format for declaring and operating a file:

The first statement declares the variable fp as a “pointer to the data type FILE”. As stated earlier, FILE is a structure that is defined in the I/O library. The second statement opens the file named file name and assigns an identifier to the FILE type pointer fp.

The second statement also specifies the purpose of opening this file. The mode does this job. Mode can be one of the following:

r  -- >   open the file for reading only

w  -- >  open the file for writing only

a   -- >  open the file for appending ( or adding ) data to it

For Example:

File *p1, *p2 ;

p1 = fopen (“data”, “r”);

p2 = fopen (“results”, “w”);

---

Previous                                                                                    Next

---