Explain the Random accessing files in C language

Random accessing of files in C language can be done with the help of the following functions −

• ftell ( )
• rewind ( )
• fseek ( )

ftell ( )

It returns the current position of the file ptr.

The syntax is as follows −

int n = ftell (file pointer)

For example,

FILE *fp;
int n;
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n = ftell (fp);

Note − ftell ( ) is used for counting the number of characters which are entered into a file.

rewind ( )

It makes file ptr move to beginning of the file.

The syntax is as follows −

rewind (file pointer);

For example,

FILE *fp;
   -----
   -----
   rewind (fp);
   n = ftell (fp);
   printf ("%d”, n);

Output

The output is as follows −

0 (always).

fseek ( )

It is to make the file pntr point to a particular location in a file.

The syntax is as follows −

fseek(file pointer, offset, position);

Offset

• The no of positions to be moved while reading or writing.
• If can be either negative (or) positive.
  • Positive - forward direction.
  • Negative – backward direction.

Position

It can have three values, which are as follows −

• 0 – Beginning of the file.
• 1 – Current position.
• 2 – End of the file.

Example

• fseek (fp,0,2) - fp moved 0 bytes forward from the end of the file.

• fseek (fp, 0, 0) – fp moved 0 bytes forward from beginning of the file

• fseek (fp, m, 0) – fp moved m bytes forward from the beginning of the file.

• fseek (fp, -m, 2) – fp moved m bytes backward from the end of the file.

Errors

The errors related to fseek () function are as follows −

• fseek (fp, -m, 0);
• fseek(fp, +m, 2);