Write about Random Access Files ( or ) Direct Access Files?
https://www.computersprofessor.com/2016/12/write-about-random-access-files-or.html
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These are occasions, however, when
we are interested in accessing only a particular part of a file. This can be
achieved with the help of the functions fseek, ftell & rewind available
in the I/O library.
These functions are used to access
the files directly from any location .These functions are useful to move the
internal file pointer from one location to another location in a file.
1. ftell:
ftell takes a file pointer and
return a number of type long, that corresponds to the current position, that
the file pointer is advanced from the beginning of the file.
Syntax: ftell ( file pointer);
Ex: n =
ftell(fp);
n would give the relative offset of
the current position. This means that n bytes have already been read ( or
written).
2. Rewind:
Rewind takes a file pointer and
resets the position to the start of the file.
Syntax: rewind ( file pointer);
Ex: rewind(fp);
3. fseek:
fseek function is used to move the
file position to a desired location within the file. It takes the following
form:
Syntax: fseek ( file pointer, offset,
position);
Ex: fseek (fp, 30,1);
File pointer is a pointer to the
file concerned, offset is a number or variable of type long and position is
as integer number. The offset specifies the number of positions to be moved
from the location specified by position.
The position can take one of the
following 3 values:
Value Meaning
0 Beginning
of file
1 Current
position
2 End
of file
The offset may be +ve, meaning move
forwards, or –ve, meaning move back words.
When the operation is successful,
fseek returns a zero. If we attempt to move the file pointer beyond the file
boundaries, an error occurs and fseek returns -1
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