title: Adding a dynamic symbol name not work with AC_DEFINE_UNQUOTED from configure.ac
body: <p>There is a macro to <a href="https://www.gnu.org/savannah-checkouts/gnu/autoconf/manual/autoconf-2.69/autoconf.html#Defining-Symbols" rel="nofollow noreferrer">add a new symbol into</a> the resulting config.h file from a configuration file. This allows you to check the system and enable options in C/C++ applications. There are two types of macros: adding a dynamic symbol and a fixed symbol. By using AC_DEFINE_UNQUOTED, which is a macro to add a dynamic symbol, it is possible to set a symbol where the name or value is from a variable.</p>
  
  <p>Here is my simple configure.ac file</p>
  
  <pre><code>name="test"
  AC_DEFINE_UNQUOTED([USE_${name}], [1], [Enable test usage])
  </code></pre>
  
  <p>I expecte that USE_test be added into config.h as C/C++ definistion. However, the difinistion does not exist in the result config.h file.</p>
  
  <p>By running Autotools there is the following line in configure.status:</p>
  
  <pre class="lang-sh prettyprint-override"><code>D["USE_test"]=" 1"
  </code></pre>
  
  <p>This means Autotools will search the config.h.in to replace the USE_test with the new value.</p>
  
  <p>But the generated config.h.in file does not contain the following definition:</p>
  
  <pre><code>#define Use_test 1
  </code></pre>
  
  <p>So Autoheader does not run correctly?! And it is not possible to add a variable text as a symbol to config.h?!</p>
  
  <p>Where is the problem or is it possible to add a symbol with a variable name by configure.ac?</p>