C language learning process: fseek and ftell Functions

The fseek function is used to set the current read/write location of a file.

Function prototype: int fseek (File * FP, long offset, int origin );

Function: moves the FP file read/write position pointer to the specified position.

Fseek (FP, 20, seek_set); indicates to move the pointer of the read/write position of the FP file 20 bytes after the file starts.

The ftell function is used to obtain the current read/write location of a file;

Function prototype: Long ftell (File * FP)

Function: Obtain the current read/write position of the stream file. The returned value is the number of bytes that the current read/write position deviates from the file header.

Ban = ftell (FP); obtains the current read/write location of the file specified by FP and transmits the value to the variable ban.

Comprehensive application of fseek and ftell functions:

Analysis: You can use the fseek function to move the position pointer to the end of the file, and then use the ftell function to obtain the number of bytes from the file header. This number is the length of the file.

# Include <stdio. h>

Main ()

{

File * FP;

Char filename [80];

Long length;

Printf ("input file name :");

Gets (filename );

// Open the file as a binary Read File

Fp = fopen (filename, "rb ");

If (FP = NULL)

Printf ("file not found! /N ");

Else

{

// Move the file pointer to the end of the file

Fseek (FP, ol, seek_end );

// Obtain the object length;

Length = ftell (FP );

Printf ("the file length is % 1D Bytes/N", length );

Fclose (FP );

}

}

Another example:
Void main ()
{
Char infilename [128];
... // Save several characters in infilename []
Fp = fopen (infilename, "rb"); // open the file specified in the infilename Array
If (FP = NULL)
{
Result = false;
Retailmsg (1, (L "file open error: % s/n", infilename ));
Break;
}
// The following three sentences are used to calculate the object length:
Fseek (FP, 0, seek_end); // point the file pointer to the end of the file
Filesize = ftell (FP); // read the number of bytes from the file header at the current pointer position
Fseek (FP, 0, seek_set); // point the file pointer to the file header
......
}