title: error: dereferencing pointer to incomplete type ‘RSA {aka struct rsa_st}’
body: <p>I have the following code:</p>
  
  <pre><code>#include &lt;openssl/bn.h&gt;
  #include &lt;openssl/rsa.h&gt;
  
  ...
  RSA *pubkey = RSA_new();
  BIGNUM *modulus = BN_new();
  ...
  pubkey-&gt;n = BN_new();
  BN_copy(pubkey-&gt;n, modulus);
  </code></pre>
  
  <p>complied like so:</p>
  
  <pre><code>gcc rsatest.c -o rsatest -lcrypto
  </code></pre>
  
  <p>I'm getting the following error:</p>
  
  <pre><code>rsatest.c: In function ‘main’:
  rsatest.c:57:8: error: dereferencing pointer to incomplete type ‘RSA {aka struct rsa_st}’
    pubkey-&gt;n = BN_new();
          ^~
  </code></pre>
  
  <p>What is the problem here?
  Thanks.</p>