C++ :: Left Over Arguments When Calling Function Pointers
May 5, 2014
Say I have a function pointer with this definition:
void ( *pressFunc ) ( void*, void* );
And i did this function:
void functionWithOneArg ( void* testPtr );
And i did this
pressFunc = &functionWithOneArg;
One. Would C actually let me do this? ( Assigning a function with one argument to a function with two )
Two. If so, what would happen to the second argument that is passed the function when its called? Does it just get 'cut off' and only the first argument is passed?
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Nov 25, 2014
In C you can just load and call the address of a function without defining its arguments like this:
Code: int (__stdcall *pMessageBox)();
int main() {
HMODULE h=0;
h = LoadLibrary("user32.dll");
pMessageBox = GetProcAddress(h, "MessageBoxA");
// MessageBoxA
pMessageBox(0, "MessageBoxA has been called!", "MessageBox Example", MB_OK);
return 0;
}
In C++ the same code gives "too many arguments for call" error unless you define the function first with its parameters.
Is there a way to do it the same way in C++?
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Jan 29, 2015
I always have confusions while using pointers with functions both as arguments and as return type.
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Feb 2, 2013
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.
Code:
#include <stdio.h>
#include <stdlib.h>
// *** Prototype Functions ***
void Post_Results (float*);
void Calculate (float*, float*, char*, float*);
void Get_Numbers (float*, char*, float*);
[Code]......
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Mar 1, 2013
I would like to avoid throwing things in constructors as much as possible.
Is this good design to have a static class method that checks arguments the caller will give to the constructor. The documentation of the class will say, thou shall call this method to validate thine arguments before calling the constructor, or else segfault may befall thoust.
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Aug 23, 2013
I'm having some problems with a function. The function is supposed to find the two largest values in an array.
Code:
void find_two_largest( const int *a, int n, int *largest, int *second_largest){
largest = a;
int temp;
second_largest = a;
for ( int i = 1; i < n; i++){
if (*(a + i) > *largest){
temp = *largest;
[Code]....
I don't see any mistake with the code of the function, but when I try to call it inside my program it only returns 0 for both largest and second_largest.
Code:
int *find_middle( int *a, int n);
void find_two_largest(const int *a, int n, int *largest, int *second_largest);
int main()
{
int n;
[Code]...
Do I have to declare the variables largest and second_largest as normal integer variables and then pass their addresses as arguments to find_largest or is that incorrect?
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Mar 27, 2013
I have a vector of pointers inside a seperate Exam class.
vector <Question* > question_list
The Question class is my base class in which I have derived sub classes for the different types of questions (MultipleChoice, LongAnswer, etc.). I am using my vector to hold the different types of questions.
in each of those classes I have virtual "write" functions in both the base and the derived classes, that write to a file differing for each type of question.
My problem now is calling the write function from a Exam function. I've tried several methods, such as:
for (size_t i = 0; i < question_list.size(); i++) {
question_list[i].write(testfile.c_str());
}
but it comes with two errors: "error C2228:left of '.write' must have class/struct/union" along with "IntelliSense: expression must have class type"
I have made a write function for the exam class as well but am not sure what it should include since the Exam class is not a derived class of the Question class.
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Sep 4, 2012
Code:
void Class1::Func(shared_ptr<type1> parameter)
{
}
or
void Class1::Func(const shared_ptr<type1>& parameter)
{
}
or
Should I ever pass arguments/parameters to other objects using shared_ptr's or raw pointers?
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Feb 28, 2014
Which is more efficient in functions? Returning values or using pointers to redefine variables passed as arguments?
I mean either using:
void ptr_Func(int *x)
{
*x = *x+1
}
or
int ptr_Func(int x)
{
return x + 1;
}
In terms of speed, memory use etc.I want to know general efficiency, I know it will obviously vary with different uses and circumstances.
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Jul 23, 2014
This works, if just loops through till it doesn't find a space or tab than counts the index at that point then uses substr to get rid of any spaces/tabs, it's a small function and uses a goto. how to do it?
Code:
string trimLeft(string lineOfCodeToTrim){
string l = lineOfCodeToTrim;
int k =0;
for(UINT i = 0;i<l.length();i++){
[Code] ....
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Mar 19, 2013
I searched the web for error: C3867... and the discussions where murky or obscure.
My code excerpt is:
#pragma once
#include <windows.h>
#include <stdlib.h>
#include <process.h>
void PutUpfrmIO(void *);
namespace WordParsor {
[Code] .....
I get the generic message:
error C3867: 'WordParsor::Form1::PutUpfrmIO': function call missing argument list; use '&WordParsor::Form1::PutUpfrmIO' to create a pointer to memberc:userskingc++wordparsorwordparsorForm1.h... and the suggestion fix generate another error.
One person suggested the gcroot<> object wrapper... but I do not know how to modify/declair the function or its argument type.
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Jun 9, 2013
The function is supposed to return value from the file in my main, but I am getting empty value. I am trying to get better with pointer. Right now just teaching myself.
right now the only way for this code to show value is when in put the putchar(*ps) inside my readfile function. I would like to readfile to return value and print in the main function.
Code:
#include <stdio.h>
char *readfile(char filename[]);
int main(int argc, char *argv[] ) {
[Code].....
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Nov 10, 2014
Here is a sample of my question
class Base{
public:
int getNum();
private:
int numToGet;
}
class Derived: public Base {
public:
friend ostream& operator<<(ostream& output, const Derived &B);
[Code]...
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Feb 19, 2014
Is this possible?
int myfunc( int a, int b, char * c )
char a = "(int)myfunc()";
char b = "(int,int,char*)"
call(a, b, ...) // Function name and return type, params
I want to do function what registers forward what will get callback if the time is right. Basically then i dont need to edit and add extra functions into source files. I just have to include header and use register forward function. If there is anything close to this it would be perfect!
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Jun 8, 2014
I have this sample code, that calls a function in a DLL. The function Callback is provided to the DLL as an argument, in order for the DLL to notify my program of relevant changes.
sample:
#include <iostream>
#include <conio.h>
#include <windows.h>
#include <winbase.h>
#include "TcAdsDef.h"
#include "TcAdsApi.h"
using namespace std;
void _stdcall Callback(AmsAddr*, AdsNotificationHeader*, unsigned long);
[Code] ....
I would like to change this code, so that there is a Main class that opens the connection and there are several separate classes (as below) that register themselves for a specific variable and get notifications if that value is changed. The reason for this is that I want to get several notifications for several independent events and I don't want them to mix. I figured this should look something like this:
class.h
#ifndef INACLASS_H
#define INACLASS_H
#include "Main.h"
class InAClass {
public:
InAClass(Main* mainClass, std::string iolocation);
[Code] ....
Unfortunately this gives me an error:
error: cannot convert 'InAClass::Callback' from type 'void (InAClass::)(AmsAddr*, AdsNotificationHeader*, long unsigned int)' to type 'PAdsNotificationFuncEx {aka void (__attribute__((__stdcall__)) *)(AmsAddr*, AdsNotificationHeader*, long unsigned int)}'
At first I thought this was because I don't have the namespace "using namespace std;" on top, but then I should be able to find something that specifically needs to come from the std namespace and is not marked as such. I don't want to rule the option out, but so far I could not find anything like that.
An alternative explanation might be that the Callback function needs to be global, but if I make it global, how can I distinguish between several Callback functions?
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Apr 27, 2013
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
what is wrong.
Here's my code.
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Aug 3, 2013
Every time I try to use the function SaveNewCD, it doesn't write to file correctly. It writes the ~, three characters, then goes into an infinite loop.
#include<iostream>
#include<fstream>
using namespace std;
int SaveNewCD();
int OpenCD();
int main() {
char ArtistName[25];
[Code] .....
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Jul 2, 2014
I am trying to call a function through a variable
The error
|error: no match for 'operator=' (operand types are 'std::string {aka std::basic_string<char>}' and 'void')|
|warning: statement has no effect [-Wunused-value]|
||=== Build failed: 1 error(s), 1 warning(s) (0 minute(s), 0 second(s)) ===|
#include <iostream>
#include <fstream>
[Code].....
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Apr 3, 2013
I am trying to use ofstream to write in a txt file in a function called recurrently. for a simplified example:
void func_write(double x) {
ofstream myfile;
myfile << "the result = " << x << endl;
} int main() {
ofstream myfile;
[Code] .....
To this stage, it does not work, because the myfile in func_write cannot write in the txt file opened in main function. I don't want to open, append and close the txt file each time the function is called, that will take more time to execute all (imagine with 500 calls).
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Dec 28, 2013
I want to call the array from one function to another all function not a main function
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Apr 6, 2012
I have a code like this below in /root_project/main.cpp:
Code:
#include "theoraplayer/TheoraVideoClip.h"
unsigned int tex_id;
TheoraVideoManager* mgr;
TheoraVideoClip* clip;
std::string window_name="glut_player";
bool started=1;
[Code] ....
and the TheoraVideoClip.h file is in /root_project/include/theoraplayer/.
Inside of TheoraVideoClip.h there is this:
Code: TheoraVideoFrame* getNextFrame();
And when I try to compile using g++ -o app main.cpp -lGL -lglut -lGLU -ltheora -ltheoradec -ltheoraenc I'm gettin this error:
main.cpp.text+0xac2): undefined reference to `TheoraVideoClip::getNextFrame()'
Ubuntu 11.10
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Oct 24, 2013
How would I call a string that sits within a switch loop in the main function, into a separate function?
Like this:
void statistics() {
cout << "Here are the statistics for your entry: " << endl;
cout << "
The size of your entry is " << s.length() << " characters." << endl;
}
I am calling string s from this:
switch (toupper(myChoice)) {
case 'A': cin.ignore();
cout <<"
Please enter your text: ";
getline(cin, s);
[Code] ....
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Feb 20, 2013
I have two functions bool check_key(string cKey, string eKey) and bool check_digit(char digit1, char digit2), and I have declared both of them globally (is this the right terminology?) right after the "using namespace std;" and right before the "int main(){".
In the first one, I called the second one . But it is giving me the error: "no match for call to `(std::string) (int&)' ".
Code:
bool check_key(string cKey, string eKey) {
if(cKey!="" && eKey=="") return false;
if(cKey=="" && eKey=="") return true;
if(cKey=="" && eKey!="") return true;
if(cKey.length()!= eKey.length()) return false;
bool flag=true;
[Code] ....
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Jun 5, 2013
I am a bit confused about how specific one must be with arguments when declaring a function. I'll show you two functions from the book I'm using to learn C to show you what I mean.
Example 1 (greatest common denominator function):
Code:
void gcd (int u, int v) {
int temp;
printf ( "
[Code] ....
So in that function, there are exactly two arguments, because that's how many arguments the algorithm to find the gcd takes. No problem there, makes sense to me. Then further in the chapter on functions I run into this,
Example 2 (square root function):
Code:
float absoluteValue (float x) {
if ( x < 0 )
x = -x;
return x;
[Code] ....
In this second example, we have a square root function that is preceded by an absolute value function. The absolute value function has the one argument, "float x", however when this function is called within the square root function, the arguments "guess * guess * -x" are passed to it. I'm confused how this absolute value function is working with all of that inside it, when it was originally declared with just "x." The only possibility I can think of is that this expression is treated as a single unit, but I'm not sure.
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Jan 15, 2015
I am actually developing an nginx module in C.I am not to bad in C, but i got a big problem to pass argument to a vadiadic function.This function look like the well good old printf, but you put a buffer as first argument, the last address to stop to put data as second argument (in my case it is the last adress of disponible memory), a string that look like one in printf, an the other argument after.Here is the problem, the 4th last argument does not have the good value. In fact, It seem to be random value from memory. I Use gcc (Debian 4.9.1-19) 4.9.1.
Code:
/* ngx_html_log.h */
#ifndef NGX_HTML_LOG_H
#define NGX_HTML_LOG_H
#include <ngx_vasm.h>
}
[code]...
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May 26, 2013
I'm trying to create a callback wrapper for pointers to member functions of any class by using templates, std::function and std::bind. This will be used to send incoming sf::Event's to classes who register callbacks with an event manager. I based my code off of the example on this page: URL.....Here's what I have:
class EventCallback
{
std::function<bool(const sf::Event&)> func;
public:
template<typename T>
EventCallback(T* object, bool(T::*func)(const sf::Event&)) { func = std::bind(func, object, std::placeholders::_1); }
bool run(const sf::Event& evt) { return func(evt); }
};
[code]....
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