Define FUNCTION_CAST in a common header

1 files changed, 13 insertions, 0 deletions

diff --git a/examples/common/alhelpers.h b/examples/common/alhelpers.h
index 3752d218..34f73864 100644
--- a/examples/common/alhelpers.h
+++ b/examples/common/alhelpers.h
@@ -18,6 +18,19 @@ void CloseAL(void);
 int altime_get(void);
 void al_nssleep(unsigned long nsec);
 
+/* C doesn't allow casting between function and non-function pointer types, so
+ * with C99 we need to use a union to reinterpret the pointer type. Pre-C99
+ * still needs to use a normal cast and live with the warning (C++ is fine with
+ * a regular reinterpret_cast).
+ */
+#if __STDC_VERSION__ >= 199901L
+#define FUNCTION_CAST(T, ptr) (union{void *p; T f;}){ptr}.f
+#elif defined(__cplusplus)
+#define FUNCTION_CAST(T, ptr) reinterpret_cast<T>(ptr)
+#else
+#define FUNCTION_CAST(T, ptr) (T)(ptr)
+#endif
+
 #ifdef __cplusplus
 } // extern "C"
 #endif