title: warning: incompatible implicit declaration of built-in function ‘printf’ [enabled by default]
body: <p>I'm using the following C code:</p>
  
  <pre><code>#include &lt;unistd.h&gt;
  #include &lt;fcntl.h&gt;
  #include &lt;sys/types.h&gt;
  
  int main()
  {
      int file=0;
      if((file=open("testfile.txt",O_RDONLY)) &lt; -1)
              return 1;
      char buffer[19];
      if(read(file,buffer,19) != 19)  return 1;
      printf("%s\n",buffer);
  
      if(lseek(file,10,SEEK_SET) &lt; 0) return 1;
  
      if(read(file,buffer,19) != 19)  return 1;
      printf("%s\n",buffer);
      return 0;
  }
  </code></pre>
  
  <p>After compiling it produces a warning:</p>
  
  <pre><code>warning: incompatible implicit declaration of built-in 
  function ‘printf’ [enabled by default]
  </code></pre>
  
  <p>What does it mean and how do I appease the C compiler to not raise the warning?</p>