Changes between Version 2 and Version 3 of tips/c++

Timestamp:

12/17/06 11:54:12 (4 years ago)

Author:

bjornroche

Comment:

added sample code to C++ tip page

tips/c++

@@ -13 +13 @@
 }}}
 
-You do not need to use any special bindings to use !PortAudio in C++ code. The only difficulty is creating a callback function. The best way to do that, is to use a static function, which appears to the compiler a a normal C function, and have the static function call a non-static function. (You can assign a pointer to your class as the userData argument when creating a stream). This topic is covered on many C++ web sites, so try googling for the following terms:
+You do not need to use any special bindings to use !PortAudio in C++ code. The only difficulty most people have is creating a callback function. The best way to do that is to use a static function, which appears to the compiler a a normal C function, and have the static function call a non-static function. (You can assign a pointer to your class as the userData argument when creating a stream).
 
-function pointer c++ static
+For example, your .h file might look like this:
+
+{{{
+class MyPortaudioClass
+{
+[snip]
+
+int myMemberCallback(const void *input, void *output,
+  unsigned long frameCount,
+  const PaStreamCallbackTimeInfo* timeInfo,
+  PaStreamCallbackFlags statusFlags);
+
+static int myPaCallback(
+  const void *input, void *output,
+  unsigned long frameCount,
+  const PaStreamCallbackTimeInfo* timeInfo,
+  PaStreamCallbackFlags statusFlags,
+  void *userData )
+{
+  return ((MyPortaudioClass*)userData)
+     ->myMemberCallback(input, output, frameCount, timeInfo, statusFlags);
+}
+
+[snip]
+};
+}}}
+
+and your .cpp file might look like this:
+
+{{{
+int MyPortaudioClass::myMemberCallback(const void *input, void *output,
+  unsigned long frameCount,
+  const PaStreamCallbackTimeInfo* timeInfo,
+  PaStreamCallbackFlags statusFlags)
+{
+  // Do what you need (having access to every part of MyPortaudioClass)
+
+  return paContinue;
+}
+}}}
+
+Once that's setup, you can open your stream using "this" as your userData:
+
+{{{
+PaError pa_error = Pa_OpenStream(
+                    [snip]...
+                    &MyPortaudioClass::myPaCallback,      // streamCallback
+                    this);   // userData
+}}}
+
+You could also just use a reference to your class in your static function like (make sure the static function is a member of the class so
+that you have access to "private" declared variables):
+
+{{{
+MyPortaudioClass* pThis = (MyPortaudioClass*)userData;
+}}}
+
+but this adds some complexity to the code.
+
+This topic is covered on many C++ web sites, so try googling for the following terms: function pointer c++ static
+
+
+Thanks to Robert Bielik for the sample code.