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<h4 class="subsection">6.1.15 <code>CONVERT</code> specifier</h4>
<p><a name="index-g_t_0040code_007bCONVERT_007d-specifier-318"></a>
GNU Fortran allows the conversion of unformatted data between little-
and big-endian representation to facilitate moving of data
between different systems. The conversion can be indicated with
the <code>CONVERT</code> specifier on the <code>OPEN</code> statement.
See <a href="GFORTRAN_005fCONVERT_005fUNIT.html#GFORTRAN_005fCONVERT_005fUNIT">GFORTRAN_CONVERT_UNIT</a>, for an alternative way of specifying
the data format via an environment variable.
<p>Valid values for <code>CONVERT</code> are:
<ul>
<li><code>CONVERT='NATIVE'</code> Use the native format. This is the default.
<li><code>CONVERT='SWAP'</code> Swap between little- and big-endian.
<li><code>CONVERT='LITTLE_ENDIAN'</code> Use the little-endian representation
for unformatted files.
<li><code>CONVERT='BIG_ENDIAN'</code> Use the big-endian representation for
unformatted files.
</ul>
<p>Using the option could look like this:
<pre class="smallexample"> open(file='big.dat',form='unformatted',access='sequential', &
convert='big_endian')
</pre>
<p>The value of the conversion can be queried by using
<code>INQUIRE(CONVERT=ch)</code>. The values returned are
<code>'BIG_ENDIAN'</code> and <code>'LITTLE_ENDIAN'</code>.
<p><code>CONVERT</code> works between big- and little-endian for
<code>INTEGER</code> values of all supported kinds and for <code>REAL</code>
on IEEE systems of kinds 4 and 8. Conversion between different
“extended double” types on different architectures such as
m68k and x86_64, which GNU Fortran
supports as <code>REAL(KIND=10)</code> and <code>REAL(KIND=16)</code>, will
probably not work.
<p><em>Note that the values specified via the GFORTRAN_CONVERT_UNIT
environment variable will override the CONVERT specifier in the
open statement</em>. This is to give control over data formats to
users who do not have the source code of their program available.
<p>Using anything but the native representation for unformatted data
carries a significant speed overhead. If speed in this area matters
to you, it is best if you use this only for data that needs to be
portable.
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