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| <title>SWIG:Examples:go:simple</title> |
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| |
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| <tt>SWIG/Examples/go/simple/</tt> |
| <hr> |
| |
| <H2>Simple Go Example</H2> |
| |
| <p> |
| This example illustrates how you can hook Go to a very simple C program containing |
| a function and a global variable. |
| |
| <h2>The C Code</h2> |
| |
| Suppose you have the following C code: |
| |
| <blockquote> |
| <pre> |
| /* File : example.c */ |
| |
| /* A global variable */ |
| double Foo = 3.0; |
| |
| /* Compute the greatest common divisor of positive integers */ |
| int gcd(int x, int y) { |
| int g; |
| g = y; |
| while (x > 0) { |
| g = x; |
| x = y % x; |
| y = g; |
| } |
| return g; |
| } |
| </pre> |
| </blockquote> |
| |
| <h2>The SWIG interface</h2> |
| |
| Here is a simple SWIG interface file: |
| |
| <blockquote> |
| <pre> |
| /* File: example.i */ |
| %module example |
| |
| extern int gcd(int x, int y); |
| extern double Foo; |
| </pre> |
| </blockquote> |
| |
| <h2>Compilation</h2> |
| |
| These are the instructions if you are using <tt>6g</tt>/<tt>8g</tt> |
| rather than <tt>gccgo</tt>. |
| |
| <ol> |
| <li>Run <tt>swig -go <a href="example.i">example.i</a></tt>. This |
| will create the three |
| files <tt>example.go</tt>, <tt>example_gc.c</tt>, |
| and <tt>example_wrap.c</tt>. |
| <li>Compile <tt><a href="example.go">example.go</a></tt> |
| using <tt>6g</tt> or <tt>8g</tt>; e.g., <tt>6g example.go</tt>. |
| <li>Compile <tt><a href="example_gc.c">example_gc.c</a></tt> |
| using <tt>6c</tt> or <tt>8c</tt>; e.g., <tt>6c example_gc.c</tt>. |
| <li>Put the two object files together into an archive |
| named <tt>example.a</tt>; e.g., <tt>gopack grc example.a example.6 |
| example_gc.6</tt>. |
| <li>Compile the <tt><a href="example_wrap.c">example_wrap.c</a></tt> |
| file using your standard C compiler with the <tt>-fpic</tt> option; |
| e.g., <tt>gcc -c -O -fpic example_wrap.c</tt>. |
| <li>Also compile the actual code, not generated by SWIG; e.g., <tt>gcc |
| -c -O -fpic example.c</tt>. |
| <li>Put the gcc compiled object files into a shared library; |
| e.g., <tt>gcc -shared -o example.so example_wrap.o example.o</tt>. |
| <li>Compile the program which demonstrates how to use the library; |
| e.g., <tt>6g runme.go</tt>. |
| <li>Link the program; e.g., <tt>6l -o runme runme.6</tt>. |
| <li>Now you should have a program <tt>runme</tt>. |
| </ol> |
| |
| <h2>Using the extension</h2> |
| |
| The Go program which demonstrates calling the C functions from Go |
| is <a href="runme.go">runme.go</a>. |
| |
| <h2>Key points</h2> |
| |
| <ul> |
| <li>Use the <tt>import</tt> statement to load your extension module from Go. For example: |
| <blockquote> |
| <pre> |
| import "example" |
| </pre> |
| </blockquote> |
| |
| <li>C functions work just like Go functions. However, the function |
| names are automatically capitalized in order to make the names |
| visible from other Go packages. For example: |
| <blockquote> |
| <pre> |
| g := example.Gcd(42,105) |
| </pre> |
| </blockquote> |
| |
| (If there are name conflicts, you can use the <tt>%rename</tt> |
| directive in the .i file or the <tt>-rename</tt> option to Go to |
| rename one or the other symbol). |
| |
| <li>C global variables are accessed using getter and setter |
| functions. The getter function is named <tt>Get</tt> followed by |
| the capitalized name of the C variable. The Setter function |
| uses <tt>Set</tt> instead of <tt>Get</tt>. |
| <blockquote> |
| <pre> |
| a = example.GetFoo() |
| </pre> |
| </blockquote> |
| </ul> |
| |
| <hr> |
| </body> |
| </html> |
