-Catching exceptions is now supported using SWIG's %exception feature. A simple -but not too useful example is provided by the throw_exception testcase in -Examples/test-suite. You can provide your own exceptions, too. +If an error occurs in a C or C++ function, you may want to convert that error into an OCaml +exception. To do this, you can use the %exception directive. The %exception +directive simply lets you rewrite part of the generated wrapper code to include an error check. +It is detailed in full in the Exception handling with %exception section. +
+ ++In C, a function often indicates an error by returning a status code (e.g. a negative number +or a NULL pointer). Here is a simple example of how you might handle that: +
+ +
+%exception malloc {
+ $action
+ if (result == NULL) {
+ caml_failwith("Not enough memory");
+ }
+}
+void *malloc(size_t nbytes);
+
++In OCaml: +
+ ++# let a = _malloc (C_int 20000000000);; +Exception: Failure "Not enough memory". +# ++
+If a library provides some kind of general error handling framework, you can also use +that. For example: +
+ +
+%exception {
+ $action
+ if (err_occurred()) {
+ caml_failwith(err_message());
+ }
+}
+
++If no declaration name is given to %exception, it is applied to all wrapper functions. +$action is a SWIG special variable and is replaced by the C/C++ function call being wrapped. +
+ ++C++ exceptions are also easy to handle. We can catch a C++ exception and rethrow it as +an OCaml exception like this: +
+ +
+%exception getitem {
+ try {
+ $action
+ } catch (std::out_of_range &e) {
+ caml_failwith(e.what());
+ }
+}
+
+class FooClass {
+ public:
+ int getitem(int index); // Exception handling added
+ ...
+};
+
++The language-independent exception.i library file can also be used +to raise exceptions. See the SWIG Library chapter.