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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-342"></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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