File Handling
When a program is terminated, the entire data is
lost. Storing in a file will preserve data even if the program terminates.
A
file is a container in computer storage devices
used for storing data. File Handling is
the storing of data in a file using a program
Stream
A stream is basically
a sequence of data. Whatever data we use in our programming flows through a
stream.
Input and Output
Stream
If the stream acts as a source
stream for the logic unit, such as data that is transferred to be processed
from an input device to the logic unit, it is known as an input stream.
If the stream acts as a
destination stream for the output device it is known as an output stream.
Types of Files in C
We will be working with two types of files: -
1. Text
file
2. Binary
file
Text file - It stores
information in the form of ASCII characters internally and when the
file is opened, the content is readable by humans. It can be created by any
text editor with a .txt or .doc extension. Since text files are
simple, they can be edited by any text editor like Microsoft Word, Notepad,
Apple Text edit etc.
Binary file - It stores
information in the form of 0’s or 1’s and it is saved with .bin extension,
therefore it takes less space. Since it is stored in the format of a binary
number system it is not readable by humans. Therefore it is more secure than a
text file. Binary files are mostly the .bin files.
Modes of file opening
|
opening Modes of C in Standard I/O |
||
|
Mode in Program |
Meaning of Mode |
When the file doesn’t exist |
|
r |
Open a file for reading the
content. |
In case the file doesn’t exist in
the location, then fopen() will return NULL. |
|
w |
Open a file for writing the
content. |
In case the file exists, its
contents are overwritten. In case the file doesn’t exist in
the location, then it will create a new file. |
|
a |
Open a file for appending the
content. Meaning, the data of the program is
added to the file’s end in a program. |
In case the file doesn’t exist in
the location, then it will create a new file. |
|
r+ |
Open a file for both writing and
reading the content. |
In case the file doesn’t exist in
the location, then fopen() will return NULL. |
|
w+ |
Open a file for both writing and
reading. |
In case the file exists, its contents
are overwritten. In case the file doesn’t exist in
the location, then it will create a new file. |
|
a+ |
Open a file for both appending and
reading the content. |
In case the file doesn’t exist in
the location, then it will create a new file. |
Operations on files
1. Creating
a new file
2. Opening
an existing file
3. Reading
from and writing information to a file
4. Deleting
the data in the file or the file altogether
5. Closing
a file
File I/O Operations
The functions
fread/fwrite are used for reading/writing data from/to the file opened by fopen
function. These functions accept three arguments. The first argument is a
pointer to buffer used for reading/writing the data.
The fread() function reads the entire
record at a time.
Syntax
fread( & variable, size of
(structure variable), no of records, file pointer);
The fwrite()
function writes an entire record at a time.
Syntax
fwrite( & structure variable ,
size of structure variable, no of records, file pointer);
|
Function |
Syntax |
|
fopen() |
FILE
*fopen(“file_name”, “mode”); |
|
fprintf() |
fprintf(FILE
*stream, const char *format [, argument, ...]) |
|
fscanf() |
fscanf(FILE
*stream, const char *format [, argument, ...]) |
|
fputc() |
fputc(int c, FILE
*stream) |
|
fgetc() |
fgetc(FILE
*stream) |
|
fclose() |
fclose( FILE *fp
) |
|
|
fseek(FILE *stream, long int offset, int whence) How to Create a File FILE *fp;
fp = fopen ("file_name", "mode"); Eg 1.The program below shows how to perform read to a file #include <stdio.h> int main() { FILE * file; char str; if (file =
fopen("hello.txt", "r")){ while((str=fgetc(file))!=EOF) printf("%c",str); } fclose(file); return 0; } Eg 2.The program below shows how to
perform writing to a file #include <stdio.h> int main() { int i; FILE * fptr; char fn[50]; char str[] = "Modern
Progressive\n"; fptr =
fopen("fputc_test.txt", "w"); // "w" defines "writing mode" for (i = 0; str[i] != '\n';
i++) { /*
write to file using fputc() function */
fputc(str[i], fptr); } fclose(fptr); return 0;
} Random Access to a File In a random-access file, we may
quickly search for data, edit it or even remove it. Random accessing of files in C language can be done
with the help of the following functions −
ftell ( ) It returns the
current position of the file ptr. The syntax is as
follows − int n = ftell (file pointer) rewind ( ) It makes file ptr
move to beginning of the file. The syntax is as
follows − rewind (file pointer); fseek ( ) It is to make the
file pntr point to a particular location in a file. seek() function
can be used to find a specific record in a file The syntax is as
follows − fseek(file pointer, offset,
position); Offset
|
Milan Tomic
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