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dyncallback(3)        DragonFly Library Functions Manual        dyncallback(3)

NAME
     dyncallback - callback interface of dyncall

SYNOPSIS
     #include <dyncall_callback.h>

     DCCallback *
     dcbNewCallback(const char * signature, DCCallbackHandler * funcptr,
         void * userdata);

     void
     dcbInitCallback(DCCallback * pcb, const char * signature,
         DCCallbackHandler * funcptr, void * userdata);

     void
     dcbFreeCallback(DCCallback * pcb);

     void
     dcbGetUserData(DCCallback * pcb);

DESCRIPTION
     The dyncallback dyncall library has an interface to create callback
     objects, that can be passed to functions as callback arguments. In other
     words, a pointer to the callback object can be "called", directly. The
     callback handler then allows iterating dynamically over the arguments
     once called back.

     dcbNewCallback() creates a new callback object, where signature is a
     signature string describing the function to be called back (see manual
     for format). This is needed for dyncallback dyncallback to correctly
     prepare the arguments passed in by the function that calls the callback
     handler. Note that the handler doesn't return the value specified in the
     signature, directly, but simply 'i' or 'f' depending on whether it is a
     integral or floating point type. The return value itself is stored where
     the handler's 3rd parameter points to (see example).  funcptr is a
     pointer to the dyncallback dyncallback callback handler (see below), and
     userdata a pointer to arbitrary user data you want to use in the callback
     handler.  Use the returned pointer as callback argument in functions
     requiring a callback function pointer.

     dcbInitCallback() (re)initialize the callback object.

     dcbFreeCallback() destroys and frees the callback handler.

     dcbGetUserData() returns a pointer to the userdata passed to the callback
     object on creation or initialization.

     Declaration of a dyncallback handler (following function pointer
     definition in dyncallback/dyncall_callback.h):

           char cbHandler(DCCallback* cb,
                          DCArgs*     args,
                          DCValue*    result,
                          void*       userdata);

     cb is a pointer to the DCCallback object in use dyncallback result is a
     pointer to a DCValue object in order to store the callback's return value
     (output, to be set by handler). Finally, userdata is a pointer to some
     user defined data that can be set when creating the callback object.  The
     handler itself returns a signature character (see manual for format)
     specifying the data type used for result.

EXAMPLE
     Let's say, we want to create a callback object and call it. For
     simplicity, this example will omit passing it as a function pointer to a
     function (e.g. compar in qsort(), etc.) and demonstrate calling it,
     directly. First, we need to define our callback handler - the following
     handler illustrates how to access the passed- in arguments:

           char cbHandler(DCCallback* cb,
                          DCArgs*     args,
                          DCValue*    result,
                          void*       userdata)
           {
             int* ud = (int*)userdata;
             int       arg1 = dcbArgInt     (args);
             float     arg2 = dcbArgFloat   (args);
             short     arg3 = dcbArgShort   (args);
             double    arg4 = dcbArgDouble  (args);
             long long arg5 = dcbArgLongLong(args);

             // .. do something ..

             result->s = 1244;
             return 'i';
           }

     Note that the return value of the handler is a signature character, not
     the actual return value, itself, and note that the actual return value is
     of type short.  Now, let's call it through a DCCallback object:

             DCCallback* cb;
             short result = 0;
             int userdata = 1337;
             cb = dcbNewCallback("ifsdl)s", &cbHandler, &userdata);
             result = ((short(*)(int, float, short, double, long long))cb)
               (123, 23.f, 3, 1.82, 9909ll);
             dcbFreeCallback(cb);

SEE ALSO
     dyncall(3), dynload(3) and the dyncall manual (available in PDF format)
     for a way more detailed documentation of this library.

AUTHORS
     Daniel Adler <dadler@uni-goettingen.de>
     Tassilo Philipp <tphilipp@potion-studios.com>

DragonFly 6.5-DEVELOPMENT       April 26, 2024       DragonFly 6.5-DEVELOPMENT