#ifndef DOXYGEN_SKIP
/* $Id: RFC7_VSILAPI.dox,v 1.1 2006/11/02 16:23:39 fwarmerdam Exp $ */
#endif /* DOXYGEN_SKIP */

/*!
\page rfc7_vsilapi RFC 7: Use VSILFILE for VSI*L Functions

Author: Eric D&ouml;nges<br>
Contact: Eric.Doenges@gmx.net<br>
Status: Proposed<br>

\section rfc7_purpose Purpose

To change the API for the VSI*L family of functions to use a new data-type
VSILFILE instead of the current FILE.

\section rfc7_background Background, Rationale

Currently, GDAL offers two APIs to abstract file access functions (referred to
as VSI* and VSI*L in this document). Both APIs claim to operate on FILE
pointers; however, the VSI*L functions can only operate on FILE pointers
created by the VSIFOpenL function. This is because VSIFOpenL returns a pointer
to an internal C++ class typecast to a FILE pointer, not an actual FILE pointer.
This makes it impossible for the compiler to warn when the VSI* and VSI*L
functions are inappropriately mixed.

\section rfc7_proposal Proposed Fix

A new opaque data-type VSILFILE shall be declared. All VSI*L functions shall
be changed to use this new type instead of FILE. Additionally, any GDAL code
that uses the VSI*L functions must be changed to use this data-type as well.

\section rfc7_compatibility Compatibility Issues, Transition timeline

In order to allow the compiler to detect inappropriate parameters passed to
any of the VSI*L functions, VSILFILE would have to be declared with the help
of an empty forward declaration, i.e.
<pre>
typedef struct VSILFILE VSILFILE
</pre>
with the struct VSILFILE itself left undefined. However, this would break
source compatibility for any existing code using the VSI*L API.

Therefore, VSILFILE* will be declared as a void pointer for now, and the change
to a distinct pointer type deferred to a future release of gdal that is not
constrained with backward compatibility issues. While this will not solve the
primary issue (no warnings/errors from the compiler), looking at the
declarations of the VSI*L functions will at least make it immediately clear
that these functions cannot be expected to work if passed a FILE pointer.

*/
 
