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### 1.1 Introduction

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.

The Python interface is a very simple wrapping of this C++ API generated automatically with SWIG. The two interfaces are identical, except for language syntax.

#### 1.1.1 If you’ve used the C API

To show how much easier the VIPS C++ API is to use, compare Figure 2.2.5 to Figure 1.1. Figure 1.2 is the same thing in Python.

A typical build line for the C++ program might be:

g++ invert.cc \ ‘pkg-config vipsCC-7.14 \ --cflags --libs‘

The key points are:

- You just include <vips/vips> — this then gets all of the other includes you need. Everything is in the vips namespace.
- The C++ API replaces all of the VIPS C types — IMAGE becomes VImage and so on. The C++ API also includes VDisplay, VMask and VError.
- Image processing operations are member functions of the VImage class — here, VImage( argv[1] ) creates a new VImage object using the first argument to initialise it (the input filename). It then calls the member function invert(), which inverts the VImage and returns a new VImage. Finally it calls the member function write(), which writes the result image to the named file.
- The VIPS C++ API uses exceptions — the VError class is covered later. If you run this program with a bad input file, for example, you get the following output:

  example% invert jim fred invert: VIPS error: im_open: "jim" is not a supported format

#include <iostream> #include <vips/vips> int main( int argc, char ⋆⋆argv ) { if( argc != 3 ) { std::cerr << "usage: " << argv[0] << " infile outfile\n"; exit( 1 ); } try { vips::VImage fred( argv[1] ); fred.invert().write( argv[2] ); } catch( vips::VError e ) { e.perror( argv[0] ); } return( 0 ); }

Figure 1.1: | invert program in C++

#!/usr/bin/python import sys from vipsCC import ⋆ try: a = VImage.VImage (sys.argv[1]) a.invert ().write (sys.argv[2]) except VError.VError, e: e.perror (sys.argv[0])

Figure 1.2: | invert program in Python

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