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  <h3 class="sectionHead"><span class="titlemark">1.1    </span> <a 
 id="x6-50001.1"></a>Introduction</h3>
<!--l. 2--><p class="noindent" ><a name="nip_label_sec:cpp"></a>
<!--l. 4--><p class="indent" >  This chapter describes the C++ API for the VIPS image
processing library. The C++ API is as efficient as the C
interface to VIPS, but is far easier to use: almost all
creation, destruction and error handling issues are handled
for you automatically.                             <!--l. 9--><p class="indent" >    The Python interface is a very simple wrapping of
  this C++ API generated automatically with SWIG. It
  adds a few utility methods noted below, but otherwise
  the two interfaces are identical other than language
  syntax.
  <!--l. 14--><p class="noindent" >
      <h4 class="subsectionHead"><span class="titlemark">1.1.1    </span> <a 
 id="x6-60001.1.1"></a>If you&#8217;ve used the C API</h4>
  <!--l. 16--><p class="noindent" >To show how much easier the VIPS C++ API is to use,
  compare Figure&#x00A0;<a 
href="vipsmanualse8.html#x14-420002.2.5">2.2.5<!--tex4ht:ref: fg:negative --></a> to Figure&#x00A0;<a 
href="#x6-60011">1.1<!--tex4ht:ref: fg:invert-c++ --></a>. Figure&#x00A0;<a 
href="#x6-60022">1.2<!--tex4ht:ref: fg:invert-py --></a> is the same
  thing in Python.
  <!--l. 19--><p class="indent" >    A typical build line for the C++ program might be:
                                                                                       

                                                                                       
  <div class="verbatim" id="verbatim-1">
g++&#x00A0;invert.cc&#x00A0;\
&#x00A0;<br />&#x00A0;&#x00A0;&#8216;pkg-config&#x00A0;vipsCC-7.18&#x00A0;\
&#x00A0;<br />&#x00A0;&#x00A0;&#x00A0;&#x00A0;--cflags&#x00A0;--libs&#8216;
</div>
<!--l. 25--><p class="nopar" >
<!--l. 27--><p class="indent" >  The key points are:
    <ul class="itemize1">
    <li class="itemize">You just include <span class="obeylines-h"><span class="verb"><span 
class="pcrr7t-">&#x003C;vips/vips&#x003E;</span></span></span> &#8212; this then gets
    all of the other includes you need. Everything is in
    the <span class="obeylines-h"><span class="verb"><span 
class="pcrr7t-">vips</span></span></span> namespace.
    </li>
    <li class="itemize">The C++ API replaces all of the VIPS C types &#8212;
    <span class="obeylines-h"><span class="verb"><span 
class="pcrr7t-">IMAGE</span></span></span> becomes <span class="obeylines-h"><span class="verb"><span 
class="pcrr7t-">VImage</span></span></span> and so on. The C++ API
    also includes <span class="obeylines-h"><span class="verb"><span 
class="pcrr7t-">VDisplay</span></span></span>, <span class="obeylines-h"><span class="verb"><span 
class="pcrr7t-">VMask</span></span></span> and <span class="obeylines-h"><span class="verb"><span 
class="pcrr7t-">VError</span></span></span>.
    </li>
    <li class="itemize">Image processing operations are member functions
    of                             the                             <span class="obeylines-h"><span class="verb"><span 
class="pcrr7t-">VImage</span></span></span>
    class  &#8212;  here,  <span class="obeylines-h"><span class="verb"><span 
class="pcrr7t-">VImage(</span><span 
class="pcrr7t-">&#x00A0;argv[1]</span><span 
class="pcrr7t-">&#x00A0;)</span></span></span> creates  a
    new  <span class="obeylines-h"><span class="verb"><span 
class="pcrr7t-">VImage</span></span></span> object  using  the  first  argument  to
    initialise  it  (the  input  filename).  It  then  calls  the
    member  function  <span class="obeylines-h"><span class="verb"><span 
class="pcrr7t-">invert()</span></span></span>,  which  inverts  the
    <span class="obeylines-h"><span class="verb"><span 
class="pcrr7t-">VImage</span></span></span> and  returns  a  new  <span class="obeylines-h"><span class="verb"><span 
class="pcrr7t-">VImage</span></span></span>.  Finally  it
    calls the member function <span class="obeylines-h"><span class="verb"><span 
class="pcrr7t-">write()</span></span></span>, which writes
    the result image to the named file.
    </li>
    <li class="itemize">The   VIPS   C++   API   uses   exceptions   &#8212;   the
    <span class="obeylines-h"><span class="verb"><span 
class="pcrr7t-">VError</span></span></span> class  is  covered  later.  If  you  run  this
    program with a bad input file, for example, you get
    the following output:
                                                     <div class="verbatim" id="verbatim-2">
          $&#x00A0;invert&#x00A0;jim&#x00A0;fred
    &#x00A0;<br />invert:&#x00A0;VIPS&#x00A0;error:&#x00A0;format_for_file:
    &#x00A0;<br />&#x00A0;&#x00A0;file&#x00A0;"jim"&#x00A0;not&#x00A0;found 
</div>
   <!--l. 57--><p class="nopar" >
   </li></ul>
                                                                                       

                                                                                       
<!--l. 62--><p class="indent" >  <a 
 id="x6-60011"></a><hr class="float"><div class="float" 
>
                                           
                                                                                       

                                                                                       
<div class="verbatim" id="verbatim-3">
#include&#x00A0;&#x003C;iostream&#x003E;
&#x00A0;<br />#include&#x00A0;&#x003C;vips/vips&#x003E;
&#x00A0;<br />
&#x00A0;<br />int
&#x00A0;<br />main&#x00A0;(int&#x00A0;argc,&#x00A0;char&#x00A0;&#x22C6;&#x22C6;argv)
&#x00A0;<br />{
&#x00A0;<br />&#x00A0;&#x00A0;if&#x00A0;(argc&#x00A0;!=&#x00A0;3)
&#x00A0;<br />&#x00A0;&#x00A0;&#x00A0;&#x00A0;{
&#x00A0;<br />&#x00A0;&#x00A0;&#x00A0;&#x00A0;&#x00A0;&#x00A0;std::cerr&#x00A0;&#x003C;&#x003C;&#x00A0;"usage:&#x00A0;"&#x00A0;&#x003C;&#x003C;&#x00A0;argv[0]&#x00A0;&#x003C;&#x003C;&#x00A0;"&#x00A0;infile&#x00A0;outfile\n";
&#x00A0;<br />&#x00A0;&#x00A0;&#x00A0;&#x00A0;&#x00A0;&#x00A0;return&#x00A0;(1);
&#x00A0;<br />&#x00A0;&#x00A0;&#x00A0;&#x00A0;}
&#x00A0;<br />
&#x00A0;<br />&#x00A0;&#x00A0;try
&#x00A0;<br />&#x00A0;&#x00A0;{
&#x00A0;<br />&#x00A0;&#x00A0;&#x00A0;&#x00A0;vips::VImage&#x00A0;fred&#x00A0;(argv[1]);
&#x00A0;<br />
&#x00A0;<br />&#x00A0;&#x00A0;&#x00A0;&#x00A0;fred.invert&#x00A0;().write&#x00A0;(argv[2]);
&#x00A0;<br />&#x00A0;&#x00A0;}
&#x00A0;<br />&#x00A0;&#x00A0;catch&#x00A0;(vips::VError&#x00A0;e)
&#x00A0;<br />&#x00A0;&#x00A0;{
&#x00A0;<br />&#x00A0;&#x00A0;&#x00A0;&#x00A0;e.perror&#x00A0;(argv[0]);
&#x00A0;<br />&#x00A0;&#x00A0;}
&#x00A0;<br />
&#x00A0;<br />&#x00A0;&#x00A0;return&#x00A0;(0);
&#x00A0;<br />}
</div>
<!--l. 88--><p class="nopar" >
<br /><div class="caption" 
><span class="id">Figure&#x00A0;1.1: </span><span  
class="content"><span 
class="pcrr7t-">invert </span>program in C++</span></div><!--tex4ht:label?: x6-60011 -->
                                           
                                                                                       

                                                                                       
  </div><hr class="endfloat" />
                                           
                                                                                       

                                                                                       
<!--l. 94--><p class="indent" >  <a 
 id="x6-60022"></a><hr class="float"><div class="float" 
>
                                           
                                                                                       

                                                                                       
<div class="verbatim" id="verbatim-4">
#!/usr/bin/python
&#x00A0;<br />
&#x00A0;<br />import&#x00A0;sys
&#x00A0;<br />from&#x00A0;vipsCC&#x00A0;import&#x00A0;&#x22C6;
&#x00A0;<br />
&#x00A0;<br />try:
&#x00A0;<br />&#x00A0;&#x00A0;a&#x00A0;=&#x00A0;VImage.VImage&#x00A0;(sys.argv[1])
&#x00A0;<br />&#x00A0;&#x00A0;a.invert&#x00A0;().write&#x00A0;(sys.argv[2])
&#x00A0;<br />except&#x00A0;VError.VError,&#x00A0;e:
&#x00A0;<br />&#x00A0;&#x00A0;e.perror&#x00A0;(sys.argv[0])
</div>
<!--l. 105--><p class="nopar" >
<br /><div class="caption" 
><span class="id">Figure&#x00A0;1.2: </span><span  
class="content"><span 
class="pcrr7t-">invert </span>program in Python</span></div><!--tex4ht:label?: x6-60022 -->
                                           
                                                                                       

                                                                                       
  </div><hr class="endfloat" />
                                           
                                                                                       

                                                                                       
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