C++ :: Function Pointer Typedef With Same Type Arguments
Mar 6, 2015
I need to create the following brain damaging abomination:
I need a function pointer type to a function that has an argument of the same function pointer type and returns the same function pointer type.
The purpose is to enable a type of subroutine threading scheme for a small application specific scripting language. The question could just as well have been posted to the C forum.
This syntax works, but Payload is a generic type which I can coerce into the right pointer type via a cast. This is ugly IMHO. I could also hide it as a pointer in the FlipState class since I've forward declared this.
But this is an extra indirection in a performance critical part of the code, and also ugly.
Code:
class FlipState ;
typedef PayLoad (*FuncPtr) (FlipState *fs, PayLoad P) ; This syntax blows chunks using gcc on the other hand. Code: class FlipState ;
typedef FuncPtr (*FuncPtr) (FlipState *fs, FuncPtr P) ;
[Code] .....
This is hardly surprising. The compiler could not possibly understand what I was defining in the typedef. I think what I need is some kind of way to forward declare a function pointer type and then redefine it properly.
Is such a think even possible or am I just SOL? This one is mind boggling. We know how to do this with classes or other complex data types, but the syntax eludes me for both C++ and C.
I have a class "Result" with a single template function Set(const std::string& arName, T& val) and a specialization of this function Set<Real>(const std::string& arName, Real& val) where Real is a typedef for double. The class is in a shared library and I use it in my main program. If I do result->Set<GLOBAL::Real>("U", 100.0); the wrong template function is called!
I check this by the output with std::cout.
Maybe it's a problem with the typedef.
If I link the object file of the Result class directly to my main program (no shared library), it works.
How this code work bcoz when pointer variable assigned in called function and how different values get as resultant output, ans 2 97 for below code. How the code wil execute so that i can validate ans
#include <stdio.h> int main() { int i = 97, *p = &i; foo(&i); printf("%d ", *p);
"Write a declaration for a function that takes two int parameters and returns an int, and declare a vector whose elements have this function pointer type."
I'm fairly new to C++ and have begun working with pointers. I wish to create am array called sigmaf_point that reads data from a text file. I have managed to get that working, but when it comes to using this pointer I come across some problems. The array is created as such:
I then create a coordinate system inside the main file, as the program I am writing is about modelling the movement of atoms, which requires you to know the coordinates:
Code: int main(); double **coords_fluid = new double*[5000]; for (int i = 0; i < n_atoms_methane; i++) { coords_fluid[i] = new double[4]; }
Now, the problem arises when I want to calculate a new variable as so:
Code: for (int i = 0; i <= n_atoms-1; i++) { sf1=sigmaf_point(coords_fluid[i][3]); }
I get the error C2064: term does not evaluate to a function taking 1 arguments, and a red line under sigmaf_point that says it must be pointer to function type. I am a bit confused about this.
So for a project, my professor sent out two pages of code containing functions to read a text file (since we do not know how to write this on our own yet). I've got the code working on Orwell IDE and it gives me 2 warnings saying
"Passing argument 1 of 'readFromFile' from incompatible pointer type"
"Passing argument 2 of 'option2Print' makes integer from pointer without a cast"
The Orwell IDE seems to just bypass these warnings and compiles the code correctly. However, when I transferred my files over to my desktop using BloodShed (what the professor uses), instead of getting a warning I get an error and the code won't compile.
I assume it will not compile on his computer either since he uses the BloodShed IDE.
I don't know how to put the code directly into the text neatly, so a attached a .zip file with my code. The "storms.txt" file is also included. (the file that will be read).
I'm given a mathematical function F(x) = etc..., the user inputs an initial x point and a final x point. The program finds the integration.
Below is a snippet of code.
/*Typedefs as given by prof*/ typedef double (*mainFunction) (double); typedef double (*calcArea) (mainFunction, double, double); int main () { answer = calcIntegral(mainFunction *curve1, calcArea *calcAreaRect, a, B)/>; /*it doesn't like this line*/ printf("The integral from %lf to %lf is: %.4lf", &a,&b,&answer); return 0; }
curve1 is a function that accepts a double and returns a double, calcAreaRect takes mainFunction main(which is F(x) so i stored the fn in curve1), double and double.
There are, or course, better ways to do this, but I need to stick to some rules:
(1) Use only pointer variables and not arrays or structs. (2) Use the three functions shown--regardless of easier methods.
The program should ask for some input, operate on those numbers, and then display the results. I know I am confused over these things:
(1) All that syntax using '*' and '&' or neither. (2) How to use the char type correctly. (3) How to use a char type input as an operator (a + b). (4) How to use the pointer of the operator variable (+,-,*,/) in an actual equation.
I'm trying to call a function via a function pointer, and this function pointer is inside a structure. The structure is being referenced via a structure pointer.
Code:
position = hash->(*funcHash)(idNmbr);
The function will return an int, which is what position is a type of. When I compile this code,
I get the error: error: expected identifier before ( token.
Is my syntax wrong? I'm not sure what would be throwing this error.
keep getting "deferencing pointer to incomplete type" on the bold lines:
main: int main(int argc, char *argv[]) { printf("Please think of an animal. I will try to find out what it is by asking you some yes/no questions."); struct treenode *root = mkTreeNode("Is it a reptile? ", NULL, NULL); struct treenode *selectedNode = root; root->left = mkTreeNode("Does it have legs?
I am doing a problem where I need to use arrays of string objects that hold 5 student names, an array of one character to hold the five students' letter grades and five arrays of doubles to hold each student's set of test scores and average score.
When I try to run it, I get these five errors.
error C2660: 'getTestScore' : function does not take 3 arguments : line 39 error C2660: 'getTestScore' : function does not take 3 arguments : line 45 error C2660: 'getTestScore' : function does not take 3 arguments : line 51 error C2660: 'getTestScore' : function does not take 3 arguments : line 57 error C2660: 'getTestScore' : function does not take 3 arguments : line 63
I came across some code and it's not clear why it is casting an unsigned char * to another pointer type only to free it right after. Here are the relevant structures:
As you can see, _Edge_Message has a *msg field, but in the function below, they cast it to the other two structure types inside the case blocks of the switch statement only to free it. What is the point or advantage of doing this?
Code: void _edje_message_free(Edje_Message *em) { if (em->msg) { int i; switch (em->type) {
I've been writing the math functions for a 3d game and tried compiling it at about 30 functions in. I get this error related to my pointers to my structures. it affects almost everything in all my functions (as youll see by looking at how i do the math in the function below). The compiler gives me the error
"error: dereferencing pointer to incomplete type"
on all my struct Type4D pointers but referencing the values in my struct TypeMatrix4X4 using pointers seems to work fine i think (it doesn't seem to complian explicitly about it. so here is the important code...
I am having trouble with this program I get the error dereferencing pointer to incomplete type in the populate function I am using BloodShed's Dev C++ compiler v4.9.9.2 I copied this program out of a book because I was having a problem with a linked list in a similar program. I think there is a problem with the compiler not supporting these types of pointer's in a function.
