devdocs/gnu_make/loaded-object-example.html


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  <h1 class="subsection">Example Loaded Object</h1>   <p>Let’s suppose we wanted to write a new GNU <code>make</code> function that would create a temporary file and return its name. We would like our function to take a prefix as an argument. First we can write the function in a file <samp>mk_temp.c</samp>: </p> <div class="example"> <pre class="example">#include &lt;stdlib.h&gt;
#include &lt;stdio.h&gt;
#include &lt;string.h&gt;
#include &lt;unistd.h&gt;
#include &lt;errno.h&gt;

#include &lt;gnumake.h&gt;

int plugin_is_GPL_compatible;

char *
gen_tmpfile(const char *nm, int argc, char **argv)
{
  int fd;

  /* Compute the size of the filename and allocate space for it.  */
  int len = strlen (argv[0]) + 6 + 1;
  char *buf = gmk_alloc (len);

  strcpy (buf, argv[0]);
  strcat (buf, "XXXXXX");

  fd = mkstemp(buf);
  if (fd &gt;= 0)
    {
      /* Don't leak the file descriptor.  */
      close (fd);
      return buf;
    }

  /* Failure.  */
  fprintf (stderr, "mkstemp(%s) failed: %s\n", buf, strerror (errno));
  gmk_free (buf);
  return NULL;
}

int
mk_temp_gmk_setup (const gmk_floc *floc)
{
  printf ("mk_temp plugin loaded from %s:%lu\n", floc-&gt;filenm, floc-&gt;lineno);
  /* Register the function with make name "mk-temp".  */
  gmk_add_function ("mk-temp", gen_tmpfile, 1, 1, 1);
  return 1;
}
</pre>
</div> <p>Next, we will write a <samp>Makefile</samp> that can build this shared object, load it, and use it: </p> <div class="example"> <pre class="example">all:
        @echo Temporary file: $(mk-temp tmpfile.)

load mk_temp.so

mk_temp.so: mk_temp.c
        $(CC) -shared -fPIC -o $@ $&lt;
</pre>
</div> <p>On MS-Windows, due to peculiarities of how shared objects are produced, the compiler needs to scan the <em>import library</em> produced when building <code>make</code>, typically called <samp>libgnumake-<var>version</var>.dll.a</samp>, where <var>version</var> is the version of the load object API. So the recipe to produce a shared object will look on Windows like this (assuming the API version is 1): </p> <div class="example"> <pre class="example">mk_temp.dll: mk_temp.c
        $(CC) -shared -o $@ $&lt; -lgnumake-1
</pre>
</div> <p>Now when you run <code>make</code> you’ll see something like: </p> <div class="example"> <pre class="example">$ make
mk_temp plugin loaded from Makefile:4
cc -shared -fPIC -o mk_temp.so mk_temp.c
Temporary filename: tmpfile.A7JEwd
</pre>
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    <a href="https://www.gnu.org/software/make/manual/html_node/Loaded-Object-Example.html" class="_attribution-link">https://www.gnu.org/software/make/manual/html_node/Loaded-Object-Example.html</a>
  </p>
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