2.7 Files  (Page 2/10)

• No special processing of the data occurs and each byte of data is transferred to or from the disk unprocessed.
• C Programming Language places no constructs on the file, and it may be read from, or written to, in any manner chosen by the programmer.

Binary files can be either processed sequentially or, depending on the needs of the application, they can be processed using random access techniques. In C Programming Language, processing a file using random access techniques involves moving the current file position to an appropriate place in the file before reading or writing data. This indicates a second characteristic of binary files – they a generally processed using read and write operations simultaneously.

For example, a database file will be created and processed as a binary file. A record update operation will involve locating the appropriate record, reading the record into memory, modifying it in some way, and finally writing the record back to disk at its appropriate location in the file. These kinds of operations are common to many binary files, but are rarely found in applications that process text files.

For all file operations you should always follow the 5-step plan as outlined below.

1. Declare file pointer.
2. Attach the file pointer to the file (open file).
3. Check file opened correctly.
4. Read or Write the data from or to the file.
5. Close the file.

Operations on files

Declarations

In C, we usually create variables of type FILE * to point to a file located on the computer.

Example

Open files

First things first: we have to open a file to be able to do anything else with it. For this, we use fopen function, like all the I/O functions, is made available by the stdio.h library. The fopen() function prototype is as follows.

In the above prototype, there are two arguments:

• filename is a string containing the name of the file to be opened. So if your file sits in the same directory as your C source file, you can simply enter the filename in here - this is probably the one you'll use most.
• mode determines how the file may be accessed.

So there are 12 different values that could be used: "rt", "wt", "at", "r+t", "w+t", "a+t" and "rb", "wb", "ab", "r+b", "w+b", "a+b".