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Guile Reference Manual

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27.5 Random Access

Scheme Procedure: seek fd_port offset whence
C Function: scm_seek (fd_port, offset, whence)
Sets the current position of fd/port to the integer offset, which is interpreted according to the value of whence.

One of the following variables should be supplied for whence:

Variable: SEEK_SET
Seek from the beginning of the file.
Variable: SEEK_CUR
Seek from the current position.
Variable: SEEK_END
Seek from the end of the file.
If fd/port is a file descriptor, the underlying system call is lseek. port may be a string port.

The value returned is the new position in the file. This means that the current position of a port can be obtained using:
 
(seek port 0 SEEK_CUR)

Scheme Procedure: ftell fd_port
C Function: scm_ftell (fd_port)
Return an integer representing the current position of fd/port, measured from the beginning. Equivalent to:

 
(seek port 0 SEEK_CUR)

Scheme Procedure: truncate-file object [length]
C Function: scm_truncate_file (object, length)
Truncates the object referred to by object to at most length bytes. object can be a string containing a file name or an integer file descriptor or a port. length may be omitted if object is not a file name, in which case the truncation occurs at the current port. position. The return value is unspecified.


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