Opening a file (fopen())
To read
and write information from file and to file respectively file must be opened.
Opening a file establishes a link between the program and operating system.
fopen() function is used to create a new file for use or opens a new existing
file for use.
Syntax:
FILE
*fp
fp=
fopen (“Filename”, “mode”);
Here,
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The first statement
declares the variable fp as a “pointer to the data type FILE” . FILE is the
structure that is defined in the I/O library. fp is a pointer variable , which
contains address of FILE.
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Fopen takes two argument.
First argument filename is a name of
file and it needs a complete path.
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The second argument is a
file opening mode. It indicates the
purpose of opening file.There are several modes available with fopen(). They
are listed as follow:
File
mode
|
Description
|
“r”
|
Opening
the file for reading.
|
“a”
|
Opening
the file for appending.
|
“w”
|
Opening
the file for writing.
|
“w+”
|
open
for the writing and reading (existing file will be overwritten).
|
“r+”
|
open
for the reading and updating (file must already exist).
|
“a+”
|
open
for the appending and reading (file may or may not exist).
|
rb
|
Opens
an existing binary file for reading.
|
wb
|
Creates
a binary file for writing.
|
ab
|
Opens
an existing binary file for appending.
|
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Both the argument file name
and mode are specified as a string . They should be enclosed in double
quotation mark.
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This function returns the
required file pointer. The value NULL will be returned, if the file cannot be
opened for any reason.
Ex,
FILE
*fp1;
fp1 =
fopen(“book.txt”, “r”);
As
shown in above example file named
book.txt will open for reading purpose. If this file does not exists ,
an error will occur.
Ex,
FILE
*fp2;
fp2 =
fopen(“mark.txt”, “w”);
As
shown in above example file named mark.txt opened for writing purpose. If this
file is already exists , its contents are deleted and file is opened as new
file.
Closing a file (fclose())
When
finish the work of file, it must be closed. It makes sure that all the
information related with the file is flushed out from the buffer and all links
to the file are broken and also restrict the misuse of file. fclose() function is used to close a
file.
Syntax:
fclose(File_ptr);
Here,
only one argument is the file pointer which is pointer to FILE structure.
If file
is closed successfully then it returns 0 or constant value EOF (End Of File) if
any error occurred.
Ex,
fclose(fp1);
As
shown in given example, the file pointing to fp1 will close.
