C++ :: Creating A Class Variable With A String?
May 12, 2013
I have defined a class in a header file; just the class, no templates involved. I have a program where I'm reading in data in string format. Each string consists of a word, a delimiter, and a variable name. Example:
cajun/mustard
I want to take that string and make it the variable name of that class type. It would be implemented along the lines of:
Code:
string str;
//read/process string here, get:
str = "mustard";
createName(str);
//pass string to creator function When the function is called, I should get the variable:
Class mustard;
Thing is, I'm not supposed to know beforehand what the variable names are, only that I create them as they are read in. It could be mustard, it could be Maynard_James_Keenan, it could even be bazinga.
My problem is, what do I do for createName()? I've looked into the concepts of pairing, Factory implementation, and maps, but I don't think they answer my question.
(P.S. if I run into the same variable name being read in twice, what steps can I take to make sure that a duplicate variable isn't created? Do I need to add in code, or does the compiler know to watch for multiple variables of the same name?)
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Dec 4, 2013
I've got 2 classes, Store and Transaction and I would like to create a priority queue of objects Transaction as a variable of Store class.
My store.h
#ifndef __STORE_H_INCLUDED__
#define __STORE_H_INCLUDED__
#include <queue>
using namespace std;
#include "Transaction.h"
struct TransactionCompare;
[Code] ....
The error im getting with this set up is
error C2664: 'bool TransactionCompare::operator ()(const Transaction &,const Transaction &)
const' : cannot convert parameter 1 from 'Transaction *' to 'const Transaction &'
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Jun 16, 2013
Any way to create a variable using a variable in the name? So E.g. if you wanted to create an int named nr(x), and x was 1, you would get an int variable named nr1? How would you do this?
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Jan 16, 2013
Please consider the following code :
#include <iostream>
using namespace std;
class superclass;
class subclass1;
class subclass2;
[Code] ....
As you can see I want to create a dynamically allocated storage of references to a parent class each of which can then point to a child class, how ever I do not know how to extract the child class out again from that array so i may access its variable b.
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Mar 2, 2013
This problem is best explained by looking at its output below. I stored 15 different values but when retrieved some are wrong.
#include <iostream>
using namespace std;
class A {
public:
int ** pointer;
[Code] ....
I need to store and retrieve the 15 different values correctly. How to solve this? The main thing is, I need to store the pointer in class A objects.
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Oct 24, 2014
How do you prompt the user to enter the number of elements for the array and use that information to creatr a variable length array? And then how do you prompt the user to enter in a number for each element of the array and scan in the appropriate numbers? the numbers are double precision floating point.
for example,
Enter the numbe of elements in the array: 3
Enter element 0: 3
Enter element 1: -1
Enter element 2: 4
I know it starts with
int main() {
double N;
int a[size];
printf("Enter the number of elements in the array:" );
scanf("%f", &size);
//I'm pretty sure this is wrong
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Dec 11, 2013
I'm attempting to split a large binary file into smaller manageable files for analysis. I've written most of the software but I'm stuck in a couple of places.
1. The binary file is split by looking at a couple of bytes to determine when to create a new file or continue appending to the current new file. The question is when I need to create a new file, how can I dynamically sign it a name? My intention is to rename each subfile by: "original_name" + new section id + ".log".
2. The start of each section is determined by a specific pattern (6 bytes of FF's). I'm running into an issue where the pattern check is checking for 5 bytes instead of 6 because the for..loop doesn't increment for one instance.
I've attached the code I have so far.
#include <iostream>
#include <stdlib.h>
#include <stdio.h>
#include <string>
#include <sstream>
using namespace std;
int append_to_file(FILE *f,long sec_start, long sec_end)
[Code] ...
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Jan 6, 2012
I am making two classes using the juce library [URL] ....
this is a problem that has now come up after solving an earlier problem i posted but its a completely seperate issue.
i have a class for loading a file when i button is clicked that seems to work. Here is the function in my LoadButton cpp:
void LoadButton::buttonClicked(Button* button)
{
FileChooser pedoFileChooser ("Choose an Audio File", File::nonexistent, String::empty, true);
if (pedoFileChooser.browseForFileToOpen())
{
File pedoFile (pedoFileChooser.getResult());
}
}
I want to be able to then use the file stored in pedoFile in the cpp of another class called PlayButton. I tried doing this with a pointer? not sure if that's correct way of doing it (i know very little about C++ or programming) by changing the function to this. I'm getting the error invalid initialisation of non-const reference of type 'juce::File*&' from a temporary of type 'juce::File'
void LoadButton::buttonClicked(Button* button)
{
FileChooser pedoFileChooser ("Choose an Audio File", File::nonexistent, String::empty, true);
if (pedoFileChooser.browseForFileToOpen())
{
File* &pedoFile = (pedoFileChooser.getResult());
}
}
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Sep 8, 2013
I have to write a loop assigning a variable x to all positions of a string variable and I'm stuck. I don't have extensive experience with arrays and I'm also a bit confused about C-String. The problem is below.
"Given the following declaration and initialization of the string variable, write a loop to assign 'X' to all positions of this string variable, keeping the length the same.
char our_string[15] = "Hi there!";
(Please note this is a 'C-string', not C++ standard string.)"
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May 15, 2013
In the following code:
#include <iostream> // For stream I/O
using namespace std;
int function(int a) {
return a;
}
int main() {
function(int b);
}
Why is creating a variable inside the function argument list not allowed. Any reason other then for the language syntax or just for the language syntax?
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May 14, 2012
I am doing a piece of gui code on some embedded system.
I'm trying to find a way of eliminating the local variable kEvent:
Code:
EVENT kEvent;
....
Code:
kEvent = EVENT_UPSTREAM;
xStatus = xQueueSendToBack(getEventProcessorQueue(),&kEvent, 0 );
....
I tried this, it doesn't work:
Code:
xStatus = xQueueSendToBack(getEventProcessorQueue(),(EVENT *)EVENT_UPSTREAM, 0 );
Shouldn't this work?
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Apr 10, 2013
I receive messages over a bus. Suppose there is a function to read the messages storing them into a struct defined as follows:
typedef struct
{
ULONG timestamp;
BYTE ID;
BYTE data_length;
BYTE data[8];
} MSG_FRAME;
Depending on the message ID different messages represent different values for one project.For example msg with ID 10 can include in the 8 bytes something like:
width: 6 bits
height: 6 bits
actpos: 12 bits
maxpos: 12 bits
minpos: 12 bits
range: 16 bits
total: 64 bits = 8 bytes
Printing the message is no big deal. But here comes the tricky part. I want to print out the specific information hidden in the 8 bytes. I can define the structures for every msg ID and compile the program with this "special" header file, but I want to do it during runtime of the program, loading the information regarding the msgs, because i can have different projects where the information for different msg IDs can differ.
I've a non-C file, where basically all the information is written. Lets stay frame named
GetStatus{
bit 0 - 7 width
bit 8 - 15 height
.
.
}
etc.
How to read it on runtime and decode the messages? On runtime I'm not able to create variables and structures anymore!
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Sep 20, 2013
Suppose I have two classes A and B so how to access object of class A in constructor of B's class as a parameter.
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May 18, 2014
I'm expected to get a starting minimum input, and also an ending maximum output (for example: 21, and 25). From here, i have to give output using all the numbers (in a row) between the min and max numbers.
(for the same example:
21
22
23
24
25)
I assumed I would want to create an array using a variable, but i'm not sure of that either.
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Apr 4, 2014
Define a constant PI that has a value of 3.14159
- Create a double variable, Radius with an initial value of 10
- Create two double variables. Circum and Area, without initialization
- Using the following formulas, compute circumference and area of the circle:
circumference = pi * r * 2 (here, r means radius)
area = pi * r * r
- Display the result using three variables (numbers must come from variables)
- Expected output: (Don’t forget to display the period at the end of the first line)
Circle with radius of 10.
Circumference = 62.8318 Area = 314.159
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Oct 12, 2013
I have an example where I have a variable belonging to a base class, but I would like to tell the compiler that it actually belongs to a derived class. How can I do this?
// base class: R0
// derived class: R1
// see function SetR1 for the problem
class R0 {
public:
int a;
[Code] .....
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Nov 9, 2013
I am trying to access a variable from another class through another class but it is not returning its "instance"?
Example:
Class View
Code:
...
V3D_Viewer viewer;
...
Class MainWindow
Code:
...
viewer* myView;
myView = new viewer();
...
Class Test
Code:
...
MainWindow window;
window.myView->setBackgroundColor(WHITE);
...
I am new to c++ references and pointers,
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Aug 2, 2013
I'm currently reading the C++ Guide for Dummies
Anyway right now I'm working with pointers and classes, and when I create a new pointer for my class it looks like this...
Pen *Pointerpen = new Pen;
But in the book they threw in this...
Pen *Pointerpen = new Pen();
Can you actually designate memory space for a function? Or was this a typo on their part? It's never come up before and they didn't explain it.
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Nov 15, 2014
I was trying to implement own vector class and wrote some code. Below is the code.
Code: #include<iostream>
#include<vector>
using namespace std;
template <typename T> class MyVector
{
T *mem;
int m_size,final_size;
public:
MyVector() : final_size(1),m_size(4)
{
[code].....
I have question on this function.
Code: myVecPush_back(T t){}
Here I was able to put elements upto any number of time, but I have allocated memory to only 4 elements in T *mem.
My question, why the program is not crashing when I tried to put elements more that 4?
Is since the variable is of type Template? Any specific reason for this?
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Feb 16, 2014
I am currently working on a "bag" class which is sort of a common sense answer to creating a random class with difference functions. I am attempting to create a "union" function which takes two bags ie: bag1 and bag2, adds all the items in both bags and creates a new bag ie: "bag3". For some reason I keep coming up with problems instead of solutions. Maybe it's the fact I just got done with 2 days of calculus. I don't know. My code is below. Both a main(source) and header file.
Header
#ifndef BAG_H
#define BAG_H
const int BAG_CAPACITY = 20;
template <typename T>
class Bag {
private:
int count; // Number of items in the Bag
[code]....
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Mar 2, 2014
I have a background in c# and am very frustrated with c++. If I created a class in c# like so:
public class Memory{
int x = 0;
int y = 0;
int height = 0;
int width = 0;
string firstname = "Bob";
string lastame = "Chester";
}
and then created a new instance of this class from a separate class by doing:
public class Main{
Memory mem = new Memory();
}
I have raked the internet for a way to create a new instance of a class in c++ while keeping its default values and have come up empty handed.
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May 16, 2013
I've just recently moved from Visual Basic 6 over to C++ and decided that I would try and write a class to mimic the Get/Set behavior seen in a variety of other programming languages. So instead of just using an overloaded function, i.e:
Code:
class NoProp {
LPCWSTR m_Title;
public:
void Title(LPCWSTR NewValue) {m_Title = NewValue;};
LPCWSTR Title() {return m_Title;};
[code].....
So far this code only works with the LPCWSTR type (const wchar_t*). Unfortunately I got to this stage using only that type, and now when I try another type, such as int, it fails. When using the int type I believe it creates an error because the constructor of InitProp expects a type of pointer to be parsed. When I try using it with int* type (the private variable then becoming int **m_Variable) it compiles, thought I cannot access the property like a normal int.
My best guess from here is that I probably have to overload the InitProp constructor in a way that it can setup the Property classes for base-types and pointer-types, and then also modify the Property class to handle both.
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Jul 3, 2013
Creating the methods for class List
main.cpp Code: #include "List.h"
int main( )
{
List la; // create list la
la.push_front( "mom" );
la.push_back( "please" );
la.push_back( "send" );
la.push_back( "money" );
la.push_front( "hi" );
cout << "
la contains:
" << la << '
[code]...
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Oct 17, 2014
I've been given specific instructions to create an array inside a Class Matrix using a constant n. This is my class but I am getting errors. I thought that maybe I had to initialize the const and the array using the constructor function Matrix() instead of directly in the class, but I didn't have any luck with that either.
class Matrix
{
public:
Matrix();
private:
const int n=3;
int e[n][n];
};
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Sep 16, 2014
I recently posted a question related to creating a heap template class. The ultimate goal is to create a series of classes that serve a purpose that was overlooked in the Qt library that I need for my current project.
The current "end goal" is a PriorityQueue template that uses a comparer class which is inherited from a "template interface". Basically a pure virtual class template. Perhaps that is the mistake to begin with but hopefully not. (Is this a valid approach?)The problem I am getting is that when I compile the code, it says my derived comparer class is abstract.
I will include all related classes here. I doubt it is relevant but the templates and the classes based off them are in different namespaces.Here is the comparer "template interface":
// in global namespace
template<class T>
class IIMQOBJECTS_EXPORT IQComparer {
virtual int compare(T& a, T& b) = 0;
virtual bool equals(T& a, T& b) = 0;
virtual bool isGreaterThan(T& a, T& b) = 0;
virtual bool isLessThan(T& a, T& b) = 0;
};
Here is the class that is supposed to be non-abstract but isn't recognized as such:
// in the application namespace AND IN SAME project that has the NetEventInfo class
// all functions ARE defined/implemented in a cpp file
class APPCORE_EXPORT NetEventInfoComparer : ::IQComparer<NetEventInfo*> {
public:
NetEventInfoComparer();
~NetEventInfoComparer();
[code].....
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Mar 6, 2015
Code:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <stdarg.h>
char * form(char *format, ...);
}
[code]...
So, this is the code i have problem with, as far as i can see, function form actually does the same thing that printf does.It probably puts all of the arguments sent to the function together into one string.
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