C++ :: Pointer Passed To Function Value Doesn't Change

Dec 24, 2014

when i pass a string pointer to a function such as string *str = new string(""); and pass that string to a handleElement() function e.g. handleElement(str), and i change the value in the function it simply doesn't change when the function exits as though it's passing it by value or something, even though it gives the pointer address.. I've now changed the code to use double pointers and pass the reference of the str pointer and it works but it seems ugly to use double pointers for this.

//handles when a new element is encountered when parsing and adds it to the parse tree
bool ParseBlock::handleElement(char cur, string *curString, int count, bool isOperator) {
countNode = new ParseNode(count);
//keep track of numbers and strings if they exist and insert them
if(!curString->empty()){
if(isNumber(*curString)

[code].....

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C++ :: Object That Is Passed To Function Is Changed Although No Pointer Is Passed

Mar 22, 2013

I am posting this simplified piece of code that is a bit confusing for me. There are two functions that I call. One shows the expected results but the result of the other one rather puzzles me.

//#define defineVecTyp Vec3f
#define defineVecTyp float
template <typename vecTyp>
vecTyp buildLaplacianPyramid(cv::Mat inputmat) {
vecTyp lapPyr;

[Code].....

Calling the function sum1 does not change the values stored in the variables val1 and val2. The output of the program is as follows:

val1= 1 ## val2= 10 // before the call of function sum1
val1= 1 ## val2= 10 // after the call of function sum1
sumOfVals= 22

This is quite obvious and as expected and I just pasted this piece of code as an example for better clarification.

However, if I call the function buildLaplacianPyramid and apply a function for Gaussian Blurring, this also effects the cv::Mat passed to the function. The line imshow("M1, after buildLaplacianPyramid",M1); therefore shows an image that is blurred. Since I am not passing a pointer to the cv::Mat I do not understand why this should be happening. I was assuming that there would be a copy of the cv::Mat M1 to be used within the function. Therefore I was expecting the cv::Mat M1 to retain its original value. I was expecting that all changes applied to cv::Mat inputmat within the function would not have any influence on the cv::Mat M1. Just like in my other example with the sum.

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C++ :: Coin / Money Change Code Doesn't Give Exact Change

Feb 20, 2013

My coin/money change code works when there can be an exact change each time, i.e. when the 1 cent option is available. However, when the change options are only $10, $5, $1, 25 cents and 10 cents, it does not give me what I want for instance, I wanted to get change for $237.80, I was expecting to get:

23 10's, one 5, two 1's and 8 dimes. However, the code below is giving me 23 10's, one 5, two 1's and 3 quarters (there is no option left for the 5 remaining cents).how to fix it?

Code:
#include<iostream>
#include<algorithm>
#include<vector>
using namespace std;
void change(double cents, int a[]);
int main() {
double Dollars;
double cents;

[code]...

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C++ :: Function Having Argument As A Pointer Passed By Reference

Dec 8, 2014

I have to write an example in which you use a function having as argument a pointer passed by reference in C++. Can you provide an example like this:

funz.h : void funz( int *&a );
funz.cpp : ? (1)
main.cpp:
#include "funz.h"
#include <iostream>

[Code]...

as I write in (1) and (2) ?

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C++ :: Pointer Passed Into A Function Looses Address It Points To

Mar 7, 2013

Sem is a pointer to semantic which is a struct type variable. I pass the sem into function yylex so i can fill the semantic.i and semantic.s(s points to an array). The problem is that when sem->i = a; is used inside yylex function, sem->s stops showing to the array.

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>
#include <iostream>
using namespace std;
union SEMANTIC_INFO

[Code] ...

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C++ :: Linked List Node Passed As Parameter / Argument Pointer To Pointer Notation

Jan 17, 2014

I was having problems changing the value of my head node I passed it as an argument as head which would be the address. The parameter was defined as struct node *head. like this

bool deleteNode(struct node *head, struct node *delptr)

I tried manipultaing pointer values to change head node value but it did not work. I saw some code online which used pointer to pointers(in code below) to change head node value it worked I dont fully understand why. Would like better understanding of why.

Would also like to know why the argument call needed &head instead of just head.

remove = deleteNode(&head,found); opposed to remove = deleteNode(head,found);

#include "stdafx.h"
#include<iostream>
struct node{

[Code].....

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C :: Change Arrays In Function Int Palin To Pointer

Oct 15, 2014

I'm trying to write a program to test if a string is palindromic using only pointers

Code:

#include <stdio.h>
#include <string.h>
void revstr(char* str)
}

[code]....

I need to change the arrays in the function int palin to pointers.

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C/C++ :: Why Doesn't String In Vector Change Value

Apr 22, 2014

I am trying to change the value of of time in my vector of structs. The result should output 1430 as the value of shares[1].time though I get something different.

unsigned convTime = 1430;
std::stringstream out;
out << convTime;
shares[1].time = out.str();
std::cout << shares[1].time;

But my shares[1].time stays as its original value and not 1430.

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C++ :: Containers That Doesn't Change Member Address

Jun 25, 2013

#include <iostream>
#include <vector>
using namespace std;
int main() {
int * ptr;
vector<int> data;
data.resize( 1000 );

[Code] ....

So I need container that doesn't rellocate their address, It doesn't need to be like vector that everything is in a single pointer such as

int * a = new int[2000];

I have a pointer pointing to a member of a container and it needs to remain valid... doing

vector<int *> Array;
// allocating
for( int i = 0; i < 1000; ++ i ){

Code] ...

Waste of time, allocating them and deallocate them seem to take some time too

a List is also not efficient enough because I access them based on index

It is not a int it is pointing to but a texture, for the sake of simpler example I pick int

So is there a container that doesn't change member address and allocate when it needs to expand ?

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C++ :: Function Passed By Pointers Or Reference?

Sep 28, 2014

I am going to read some codes about image processing and I need to understand functions like this one below?

BOOL Trans_Geo_Affine(CImage *pImgSrc, CImage *pImgDst, BOOL bMatrix,
BOOL bHvInversed, double fScale_xx, double fFlex_xy, double fSkew_yx,
double fRotate_yy, double fTx, double fTy, int nInterpolation, BOOL bResize, BYTE cFill)

[URL]

two parameters, CImage *pImgSrc and CImage *pImgDst. I think they are class pointers and the function is passed by reference. What should I learn to understand this function and its parameters? How should I use this function? how to use the function with two parameters CImage *pImgSrc and CImage *pImgDst.

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C/C++ :: Values Passed To Put Function But Not Having Any Effect

Feb 9, 2015

I have this code:

tgaManager.fileWriter.put((unsigned char)min(blue*255.0f,255.0f)).put((unsigned char)min(green*255.0f, 255.0f)).put((unsigned char)min(red*255.0f, 255.0f));

that should pass the value decided by the min function to an ofstream object, filewriter, that call the put method to print chars in a tga image file. When I open the file, all I see it is a huge black screen. You may be thinking that the values of blue,green and red are all zero but it is not the case.

With this code:

if (x==50 && y==50) {
cout << "Min BGR: " << endl;
cout << min (blue*255.0f,255.0f) << ' ' << min (green*255.0f,255.0f) << ' ' << min (red*255.0f,255.0f) << ' ' << x << ' ' << y << endl;

I get: Min BGR: 9.54167 29.9188 47.8701 50 50

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C++ :: Cloning Object Passed By Function?

May 21, 2014

Is it correct for me to make a clone of testobj in function AddTest below, before i add it to my map? What i want is an user pass testobj to me though AddTest, and after i add it into my map, i do not want to have anything to do with the original testobj anymore. I.e, they are two copies, one belong to Device, one belong to the caller, both has no link to each other.

Also regarding the GetTest method, i prefer to return a raw pointer, as i do not want to force the caller to use smart pointer. And i also do not want the caller to be able to do anything that may change testobj in the map. So i am not sure to return as const reference or make a clone of testobj on the map and return it to the user (but caller need to delete the testobj when it is not used).

Code:

class Device {
public:
void AddTest(const Test* const testobj) {
_pTest.insert("ss", QSharedPointer<Test>(test->clone()));
} const Test* const GetTest(QString str) {
return _pTest[str].data();

[code].....

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C++ :: Possible To Change A Single Variable From A Pointer?

Dec 2, 2013

I am stuck at a problem where I have two pointers pointing to the same object, and I need to change an int on one of the pointers but point to the same object.

To be more specific, there is an array of Item objects. A long list of items a player can buy. Then, there is the player's inventory, a vector pointer. Whenever a player buys an item, it sets the pointer to the bought object.

The problem arises when he buys two of the same object. I tried to identify the objects with an ID, but it does nothing, because they are just pointing to the same object, and so I have no way of telling them apart.

This is further complicated by the fact that it is a polymorphic object. So, I can't simply make a new every time I buy an object, without making a hassle. Well, at least I am not familiar with that kind of code just yet.

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C++ :: Change From Array To Pointer Arithmetic?

Sep 12, 2013

#include <iostream>
#include <string>
using namespace std;

[Code]....

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C++ :: Variadic Function - Parameters Get Passed In Reverse

Nov 17, 2014

I noticed that when using variadic functions, if I pass the va_arg() as parameter to a function, the parameters get passed in reverse. Is that expected?

For example, the following code outputs
Code:
1 2
2 1

Code:
#include <iostream>
#include <stdarg.h>

void foo_func(int v1, int v2)
{
std::cout << v1 << " " << v2 << std::endl;

[Code] .....

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C++ :: Function To Find Out How Many Days Have Passed Since Last Birthday

Feb 20, 2013

I have to write a c++ program with my own function which consists of two parameters (day, month). Function have to return number of days since the begining of this year. Using this function i have to find out how many days are left till birthday (or how many days have passed since last birthday)

This is how far i am:

Code:

#include <iostream>
using namespace std;
int cikDienu(int diena, int menesis);
int main()

[Code] ....

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C++ :: Global Arrays - Passed By Reference To Function

Mar 9, 2013

I currently have multiple functions that use globally declared arrays in my code.

I want to turn them so that arrays are no longer globally declared, but instead are passed by references to the function.

And I have a function caller inside main, and other functions are called within the function.

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C++ :: Multiple Objects Passed As Reference To Function

Apr 23, 2013

Essentially, the 'Sequence' below uses linked lists to store data. If 'result' refers to the same sequence as 'seq1' or 'seq2', I want 'result' to refer to a new sequence. This new sequence can be default constructed (no copy of 'seq1' or 'seq2' is required). I can't seem to do this correctly. Also, the prototype of the function cannot be altered.

void fun(const Sequence& seq1, const Sequence& seq2, Sequence& result) {
// Check for reference to same sequence. If they are the same,
// create new sequence for 'result' to refer to
if ((&seq1 == &result) || (&seq2 == &result)) {

[Code] ......

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C++ :: Unsigned Char To String And Being Passed Into Function

Mar 24, 2015

I have the following code, but it crashes on the "data = " line...

Code:
void Test(string& data) {
unsigned char* msg = (unsigned char*)malloc(MAX_LENGTH));
...
data = string(reinterpret_cast<const char*>(msg), MAX_LENGTH);
}

I know I could just return string, but what is wrong with this code that is making it crash?

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C :: Sorted List - Why Value Of Void Pointer Change

Feb 16, 2014

I have a the following in a header file.

Code:

struct SortedList{
void * data;
struct SortedList * next;
struct SortedList * previous;
int (*compareFunc)(void *, void *);
void (*destructor)(void *);

[Code] ....

In a .c file, I implemented the SLCreate function.

Code:
SortedListPtr SLCreate(CompareFuncT cf, DestructFuncT df){
struct SortedList item;
item.data = NULL;
item.next = (struct SortedList *) malloc(sizeof(struct SortedList));

[Code] ....

In main.c, I try to do the following:

Code:
SortedListPtr list = SLCreate(&compareInts, &destroy);

A bunch other code that does not alter list or it's contents at all.

struct SortedList item = (*list);
void * data = item.data;
if (data != NULL) {
printf(Why did data become not null???
"); }

How come my variable data became not null anymore when I haven't altered it at all....

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C++ :: Function Works When Passed String Literal But Not A Variable

Jul 10, 2014

I'm making a .json loader for a project that I'm working on, and to simplify things, I decided to make all the root attributes named in a separate file. Here's my problem: my loading function, Add(const char* id), works just fine when I pass it a string literal.

However, when I use a function that iterates through a vector list, even with the exact same definitions as the literal, it returns the error: std::out_of_range at memory location 0x0026fb30

I've stepped through it with the VS2010 debugger about a hundred times, checked against memory locations, and just have done everything I can think of, all to no avail..

The code, with data-checking omitted:

The std::map I'm adding to:

static std::map<const char*, Item*> *s_mItems;
Initialized as std::map<const char*, Item*> *Item::s_mItems;

Add() Function (Works by itself with a literal):

static bool Add(const char* id) {
...
std::string name = node.Get("name").ToString();
std::string desc = node.Get("description").ToString();
int rarity = StrToRarity(node.Get("rarity").ToString());

[Code] ....

AddList() function, where the program always breaks:

static void AddList(std::vector<std::string> list) {
for(std::vector<std::string>::iterator it = list.begin(); it != list.end(); it++) {
Add(it->c_str());
}
}

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C/C++ :: Find Average Of 10 Numbers Passed To Array Using Function?

Jun 20, 2012

find the average of 10 numbers to an array using function .the array should be controlled by while loop?

#include <iostream.h>
float sum(float x[],int size);
    main() {
   float a[10];
int n=10;

[Code] .....

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Visual C++ :: Check Type Of Argument Passed To Each Function?

Feb 24, 2015

How to check the type of argument passed to each function, checktype, in below?.

void checktype(void *p)
{
}
or
template <typename Type>
Type checktype(Type t) {
}

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C++ :: When User Inputs It Doesn't Show The Function

Aug 2, 2014

#include <iostream>
#include <iomanip>
#include <fstream>

[Code]....

i have already tried putting system pause or cin.get after it, but no luck

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C++ :: Display Fraction In Proper From Based On 2 Arguments Passed To Class Member Function

Mar 15, 2015

We're assigned a project working with classes and fractions. My goal is to display a fraction in proper from based on 2 arguments passed to a class member function proper();

My strategy was to utilize the greatest common factor between the 2 arguements, then divide both the numerator and denominator by that number and then it would display.

The program actually runs, but only seems to divide the numerator and not the denominator. This in return makes my other class member functions have incorrect comparisons and sums.

Code:
#include<iostream>
#include<conio.h>
class Fraction {
friend void compare(Fraction a, Fraction b);
friend void sum(Fraction a, Fraction b);

[Code] ....

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C :: Calling Function Via Function Pointer Inside Structure Pointer

Mar 14, 2013

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.

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