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| <a name="Argument-list-functions-_0025VAL_002c-_0025REF-and-_0025LOC"></a> |
| <h4 class="subsection">6.1.17 Argument list functions <code>%VAL</code>, <code>%REF</code> and <code>%LOC</code></h4> |
| <a name="index-argument-list-functions"></a> |
| <a name="index-_0025VAL"></a> |
| <a name="index-_0025REF"></a> |
| <a name="index-_0025LOC"></a> |
| |
| <p>GNU Fortran supports argument list functions <code>%VAL</code>, <code>%REF</code> |
| and <code>%LOC</code> statements, for backward compatibility with g77. |
| It is recommended that these should be used only for code that is |
| accessing facilities outside of GNU Fortran, such as operating system |
| or windowing facilities. It is best to constrain such uses to isolated |
| portions of a program–portions that deal specifically and exclusively |
| with low-level, system-dependent facilities. Such portions might well |
| provide a portable interface for use by the program as a whole, but are |
| themselves not portable, and should be thoroughly tested each time they |
| are rebuilt using a new compiler or version of a compiler. |
| </p> |
| <p><code>%VAL</code> passes a scalar argument by value, <code>%REF</code> passes it by |
| reference and <code>%LOC</code> passes its memory location. Since gfortran |
| already passes scalar arguments by reference, <code>%REF</code> is in effect |
| a do-nothing. <code>%LOC</code> has the same effect as a Fortran pointer. |
| </p> |
| <p>An example of passing an argument by value to a C subroutine foo.: |
| </p><div class="smallexample"> |
| <pre class="smallexample">C |
| C prototype void foo_ (float x); |
| C |
| external foo |
| real*4 x |
| x = 3.14159 |
| call foo (%VAL (x)) |
| end |
| </pre></div> |
| |
| <p>For details refer to the g77 manual |
| <a href="http://gcc.gnu.org/onlinedocs/gcc-3.4.6/g77/index.html#Top">http://gcc.gnu.org/onlinedocs/gcc-3.4.6/g77/index.html#Top</a>. |
| </p> |
| <p>Also, <code>c_by_val.f</code> and its partner <code>c_by_val.c</code> of the |
| GNU Fortran testsuite are worth a look. |
| </p> |
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