There are two syntactically different ways of invoking a function via a pointer.
But your first function keeps the value inside of it's scope, and once the function returns any … By clicking “Post Your Answer”, you agree to our To subscribe to this RSS feed, copy and paste this URL into your RSS reader. Whenever a class defines a virtual function (or method), most compilers add a hidden member variable to the class that points to an array of pointers to (virtual) functions … This means the above statement can also be written like this:since we are assigning the address of the function num to the pointer variable p2f.No, the adress operator is not needed, since the name of a function already “is” a pointer to the functions’s adress.No because f2p is pointer type whereas sum is function name which itslef is an address so its correctIn sum function,it should return num1+num2 as sum1 and sum2 are not declared. All of the examples are preceded by static. Through a pointer a function can be passed to other function as an argument and returned from a function. As it stands, this code is dangerous for the following reasons.A much better way to code this that avoids these problems is as followsThis approach to the use of a jump table is just as secure as an explicit switch statement, thus the idea that jump tables are dangerous may be rejected.It is well known that many C compilers will attempt to convert a switch statement into a jump table. For instance, consider the following code fragment:The above code declares pf[] to be an array of pointers to functions, each of which takes no arguments and returns void. You could go ahead and remove all the const and static declarations and the code would still work. Furthermore, the function pointer array is potentially more robust. We then define an array of TIMED_TASK, and initialize it with the list of functions that are to be called and their calling interval. The read_str contains the list of all legal mnemonic combinations. In this particular case, it is assumed that you can even declare the memory space in which parameters passed by value appear.
We determine if we have a valid command sequence by making use of the standard library function strstr(). Also, I may not be interested in returning from any of these functions (each will call the next according to some global variable). Best How To : Your code for function1 changes the value of the variable in the function only.So there are no repercussions of the change outside of the function. Also notice that when a local variable is being returned from a function, we have to declare it as static in the function. This is extreme, but is justified on pedagogical grounds.My thanks to Mike Stevens not only for reading over this manuscript and making some excellent suggestions but also for over the years showing me more ways to use function pointers that I ever dreamed was possible.This article was published in the May 1999 issue of Jones, Nigel. Void pointers are used during function declarations. The functions are all prototyped like But then I get "function call missing argument list; use '&myclass::func01'"I get "error C2440: '=' : cannot convert from 'void (__thiscall myclass::* )(unsigned char *,int,int)' to 'myclass::tfunc' Also, I may not be interested in returning from any of these functions (each will call the next according to some global variable). Executing a member via pointer to member method is left as an exercise to the reader (hint: See C++ faq pointer to member). This project was implemented using a Whitesmiths' compiler and a 68HC11 microncontroller.If any of these examples has whet your appetite for using arrays of function pointers, but you are still uncomfortable with the declaration complexity, then fear not!
But your first function keeps the value inside of it's scope, and once the function returns any … By clicking “Post Your Answer”, you agree to our To subscribe to this RSS feed, copy and paste this URL into your RSS reader. Whenever a class defines a virtual function (or method), most compilers add a hidden member variable to the class that points to an array of pointers to (virtual) functions … This means the above statement can also be written like this:since we are assigning the address of the function num to the pointer variable p2f.No, the adress operator is not needed, since the name of a function already “is” a pointer to the functions’s adress.No because f2p is pointer type whereas sum is function name which itslef is an address so its correctIn sum function,it should return num1+num2 as sum1 and sum2 are not declared. All of the examples are preceded by static. Through a pointer a function can be passed to other function as an argument and returned from a function. As it stands, this code is dangerous for the following reasons.A much better way to code this that avoids these problems is as followsThis approach to the use of a jump table is just as secure as an explicit switch statement, thus the idea that jump tables are dangerous may be rejected.It is well known that many C compilers will attempt to convert a switch statement into a jump table. For instance, consider the following code fragment:The above code declares pf[] to be an array of pointers to functions, each of which takes no arguments and returns void. You could go ahead and remove all the const and static declarations and the code would still work. Furthermore, the function pointer array is potentially more robust. We then define an array of TIMED_TASK, and initialize it with the list of functions that are to be called and their calling interval. The read_str contains the list of all legal mnemonic combinations. In this particular case, it is assumed that you can even declare the memory space in which parameters passed by value appear.
We determine if we have a valid command sequence by making use of the standard library function strstr(). Also, I may not be interested in returning from any of these functions (each will call the next according to some global variable). Best How To : Your code for function1 changes the value of the variable in the function only.So there are no repercussions of the change outside of the function. Also notice that when a local variable is being returned from a function, we have to declare it as static in the function. This is extreme, but is justified on pedagogical grounds.My thanks to Mike Stevens not only for reading over this manuscript and making some excellent suggestions but also for over the years showing me more ways to use function pointers that I ever dreamed was possible.This article was published in the May 1999 issue of Jones, Nigel. Void pointers are used during function declarations. The functions are all prototyped like But then I get "function call missing argument list; use '&myclass::func01'"I get "error C2440: '=' : cannot convert from 'void (__thiscall myclass::* )(unsigned char *,int,int)' to 'myclass::tfunc' Also, I may not be interested in returning from any of these functions (each will call the next according to some global variable). Executing a member via pointer to member method is left as an exercise to the reader (hint: See C++ faq pointer to member). This project was implemented using a Whitesmiths' compiler and a 68HC11 microncontroller.If any of these examples has whet your appetite for using arrays of function pointers, but you are still uncomfortable with the declaration complexity, then fear not!