Differences between version 5 and previous revision of CastingPointerToFunction.
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| Newer page: | version 5 | Last edited on Wednesday, January 22, 2003 4:22:37 pm | by JohnMcPherson | Revert |
| Older page: | version 4 | Last edited on Monday, November 11, 2002 12:14:09 am | by PerryLorier | Revert |
@@ -23,6 +23,27 @@
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And you need to do this why?
-1.
Jon was using it to "compile" something then jump to it in C, by casting an array as a function, then calling it.
-2.
I use it frequently to do things like have a lookup table of name to function. For example in ircu, theres a functino called "parse" which takes a line from a user, splits it up into a function and it's arguments, then scans through a table of functions and their names, when it finds one that matches that command, it calls the function with the arguments it parsed earlier. Nice 'n zippy.
+*
Jon was using it to "compile" something then jump to it in C, by casting an array as a function, then calling it.
+
+*
I use it frequently to do things like have a lookup table of name to function. For example in ircu, theres a functino called "parse" which takes a line from a user, splits it up into a function and it's arguments, then scans through a table of functions and their names, when it finds one that matches that command, it calls the function with the arguments it parsed earlier. Nice 'n zippy.
+
+* Some functions take another function as an argument. See the example below.
+
+
+from atexit(1):
+ #include <stdlib.h>
+ int atexit(void (*function)(void));
+
+you can specify functions to be executed after main() finishes.
+You do this by calling atexit(functionname), as a function name
+without () is a pointer to that function. However, if you want to this for a function that returns something other than null, you have to type cast it. Eg:
+ (int endwin() is an ncurses function).
+
+ atexit(endwin);
+ source.cpp:227: passing `int (*)()' as argument 1 of `atexit(void (*)())'
+ atexit(void)endwin);
+ source.cpp:227: void value not ignored as it ought to be
+
+The trick is to cast the pointer to a function pointer of the required type:
+ atexit( (void(*)())endwin );
