ftell(), ftello(), ftello64()

Return the current position of a stream

Synopsis:

#include <stdio.h>

long int ftell( FILE* fp );

off_t ftello( FILE* fp );

off64_t ftello64( FILE* fp );

Arguments:

fp: The stream that you want to get the current position of.

Library:

libc

Use the -l c option to qcc to link against this library. This library is usually included automatically.

Description:

The ftell(), ftello(), and ftello64() functions return the current position of the stream specified by fp. This position defines the character that will be read or written by the next I/O operation on the file. The difference between these functions is the data type of the returned position. The ftello64() function is a large-file support version of ftello().

Note: In QNX Neutrino 6.6 or later, the large-file support functions and data types appear in the name space only if you define _LARGEFILE64_SOURCE when you compile your code. For more information, see “Classification” in What's in a Function Description?

You can use the value returned by an ftell() function in a subsequent call to fseek(), fseeko(), or fseeko64() to restore the file position to a previous value.

Returns:

The current position of the file, or -1L if an error occurred (errno is set).

Examples:

#include <stdio.h>
#include <stdlib.h>

long filesize( FILE *fp )
{
    long int save_pos;
    long size_of_file;

    /* Save the current position. */
    save_pos = ftell( fp );
    
    /* Jump to the end of the file. */
    fseek( fp, 0L, SEEK_END );
    
    /* Get the end position. */
    size_of_file = ftell( fp );
    
    /* Jump back to the original position. */
    fseek( fp, save_pos, SEEK_SET );

    return( size_of_file );
}

int main( void )
{
    FILE *fp;

    fp = fopen( "file", "r" );

    if( fp != NULL ) {
        printf( "File size=%ld\n", filesize( fp ) );
        fclose( fp );
        
        return EXIT_SUCCESS;
    }
    
    return EXIT_FAILURE;
}

Classification:

ftell() is ANSI, POSIX 1003.1; ftello() is POSIX 1003.1; ftello64() is Large-file support

Safety:
Cancellation point	Yes
Interrupt handler	No
Signal handler	No
Thread	Yes