lseek man page on Ultrix

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lseek(2)							      lseek(2)

       lseek, tell - move read or write pointer

       #include <sys/types.h>
       #include <unistd.h>

       pos = lseek(d, offset, whence)
       off_t pos;
       int d, whence;
       off_t offset;

       pos = tell(d)
       off_t pos;
       int d;

       The system call moves the file pointer associated with a file or device
       open for reading or writing.

       The descriptor d refers to a file or device open for reading  or	 writ‐
       ing.  The system call sets the file pointer of d as follows:

       ·    If whence is SEEK_SET, the pointer is set to offset bytes.

       ·    If	whence	is SEEK_CUR the pointer is set to its current location
	    plus offset.

       ·    If whence is SEEK_END, the pointer is set to the size of the  file
	    plus offset.

       Seeking beyond the end of a file and then writing to the file creates a
       gap or hole that does not occupy physical space and reads as zeros.

       The system call returns the offset of the current byte relative to  the
       beginning of the file associated with the file descriptor.

   System Five
       If  you	compile	 a  program in the System Five environment, an invalid
       whence argument causes SIGSYS to	 be  sent.   This  complies  with  the
       behavior	 described  in the System V Interface Definition (SVID), Issue

Return Values
       Upon successful completion, a long integer (the	current	 file  pointer
       value)  is returned.  This pointer is measured in bytes from the begin‐
       ning of the file, where the first byte is  byte	0.   (Note  that  some
       devices	are incapable of seeking.  The value of the pointer associated
       with such a device is undefined.)  If a value of -1 is returned,	 errno
       is set to indicate the error.

       The  system call fails and the file pointer remains unchanged under the
       following conditions:

       [EBADF]	      The fildes is not an open file descriptor.

       [EINVAL]	      The whence is not a proper value.

       [ESPIPE]	      The fildes is associated with a pipe or a socket.

See Also
       dup(2), open(2)


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