C++ :: Avoiding Construction Of Object Fields?
Sep 26, 2014
I have made the following code to illustrate my problem:
#pragma once
#include <bitset>
#include <iostream>
[Code].....
Now I want to avoid my bitset field being constructed before the ConstructTest constructor is called. So at first I tried wrapping it in a unique_ptr but found out that this would give me some potential problems with const functions.
And then I realized I could just set it to NULL, as I have in the above code. I tried that, got unexpected print outs, until I found out that NULL is just equal to 0 in C++ and that the bitset has a = operator that takes a number, int, long or maybe something else. Either way, this effectively constructs the bitset and sets it to the number 0.
So my efforts so far have been shut down. But then how can I avoid the bitset being constructed in advance, if at all possible?
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Mar 25, 2014
I tryed to create program I wich u can guess number, I made some if to prevent inputting 2 times the same number It works. I tryed to apply the same process for generating
#include <cstdlib>
#include <iostream>
#include <stdlib.h>
[Code]....
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Jan 24, 2014
I have an AbstractAgent base class that manages a background thread. The actual work done in the background thread is accomplished through a pure virtual function call.
Here's the problem: because the base class is initialized prior to the derived class, there is a race condition in which the pure virtual call might occur before the derived class is initialized. Likewise, on teardown the derived class might deconstruct before the base class destructor has a chance to stop the thread.
I'd like to know if there are any well-known patterns for dealing with this problem. All I can think of is providing start() and stop() methods which can be called from the most-derived class's constructor/destructor, but that strikes me as inelegant.
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Jan 6, 2015
I've just started working on a Database application and maintaining a previous developer's code, one thing I see is that column and table names are hardcoded throughout the code which is something I'd like to avoid. To me it seems like a practice that is prone to spelling mistakes reaping havoc across the application.
Some I've looked at include:
Constant strings
const string TableName_ColumnName = "TestName";
Dictionary and Enum:
public static string GetColumnName(ColumnId inColId)
{
[Code]....
I think I prefer the second option but it means that retrieving the column names means quite a long winded function call.
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Jul 9, 2013
how to handle reallocation costs when input data is unbounded.
For instance, in a low-latency environment such as a trading platform or real-time data collection system or MMORPG where you can receive a large amount of input, you can not afford a stall while the data structure is rebuilt with a larger buffer. You can use historical data to "guess" an appropriate size but this is far from fool-proof. You can also create a sentinel thread that monitors the load factor of your data structure but that brings its own problems (e.g. another thread that needs execution time and to lock the data).
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Feb 17, 2014
I have a class which upon construction has a part which should be executed when the constructor has finished "enough" to make the call valid.
Take the following simplified class example (the actual problem is much more elaborate):
Code:
#include <functional>
class base {
public:
base(int i, std::function<void()> func) : mi(i)
[code]....
Explicitely creating a derived class allows me to properly implement the lambda to call a member of the class.
I can't seem to figure out how to do this for an explicit instantiation of the base class.
Can this be done ? Or is this a shortcoming of VS2012 or something the standard doesn't handle ?
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Feb 13, 2013
I'm trying to implement 2d array to simulate linked list for stack and I faced several difficulties doing so.
How do I implement from Top to Bottom ordering? How do I check random index value for validity?
Source-code:
Code:
#include <iostream>
using namespace std;
int myTop, index, nex = -1;
int twoDimentionalArray[25][3], L[25];
[Code].....
And one more thing: how do I get straight 0 from 25 index in the first coulumn?
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Mar 28, 2013
I am using set in my code to get fields from a reader xml which are being errored out but it is storing it in ordered form(i.e it is internally sorting it) not in accordance to how the reader xml has the fields. What should i do so that it write the errored file in accordance to the reader xml.
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Mar 28, 2013
I am using set in my code to get fields from a reader xml which are being errored out but it is storing it in ordered form(i.e it is internally sorting it) not in accordance to how the reader xml has the fields.What should i do so that it write the errored file in accordance to the reader xml.
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Jul 23, 2013
I am beginner in C++ programming. And i was try use STRTOK code with NULL fields, but in ARRAY fields NULL values is skiped. For example:
input text in Memo2:
AnsiString PAT02[100][20];
for (int IndexVRadku02 = 0; IndexVRadku02 < Memo2->Lines->Count ; IndexVRadku02++) {
AnsiString PNF02 = Memo2->Lines->Strings[IndexVRadku02];
char * PN02;
[Code] ....
Result:
Array 00 01 02 03 04 05
00 0000 TEXT1 TEXT2
01 0002 TEXT3 TEXT4 TEXT5
02 0003 TEXT6
But i need this result:
Array 00 01 02 03 04 05
00 0000 TEXT1 TEXT2
01 0002 TEXT3 TEXT4 TEXT5
02 0003 TEXT6
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Aug 9, 2014
Why do you use Private fields in a class if an outside class can change the private fields using get and set properties?
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Nov 6, 2014
How can you actually create private fields in a C struct? I got the concept of VTable and inheriting methods aswell overriding them, but private variables can be obtained with static keyword in sourcefile. If you have variables in a struct, you can access them as soon as you got a ref to the struct. The functions are easy:
Code:
struct classA {
pointerToFunction *p;
} static void* thePrivateFoo() { }
void* publicFoo() {
thePrivateFoo(); /* or something like that */
} ...
/*in init code somewhere in the c file */ classAInstance->p = publicFoo;
But I was thinking about the variables... How is this achievable? I was thinking of a struct with only get/set functions and with no datamembers at all. All vars to be static outside the struct. But this kind of destroys the encapsulation.
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Sep 16, 2013
Question: How can we write functions to access various fields?
Example: A phone number -- it has an area code, exchange & subscriber -> (123)-456-7890
How can we write a function to access the various fields of a phone number both in a particular class & in the main?
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Dec 2, 2014
is it possible to define as template the following get functions.
class Config {
public:
enum { NO_ID = 999 };
struct ValueType {
bool a;
size_t b;
std::time_t c;
[code]....
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Nov 17, 2014
reading and writing 2D arrays I've been trying out a few tutorials using FileStream but I couldn't get any of them to work.
Anyway what I'm trying to do is save the playerArray to a .txt file and then read from that .txt into the fields within the GUI. This is supposed to act as a database.
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
[Code]....
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Jun 22, 2013
Is there a way of passing values gotten from a function into a fields of a struct?
Lets say you got a function that returns sum and square of some numbers. How can I assign those values to the new made struct?
struct Struct
{
int sum_from_func;
int square_from_func;
};
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Feb 29, 2012
I'm currently working on the ioquake3 engine . The ioquake3 engine is separated into 2 different main threads at runtime: the gamecode and the engine. Both are communicating but not all information and my problem resides here.
In the gamecode, there's a struct called gentity_t which contains a lot of fields:
Code:
typedef struct gentity_s gentity_t;
struct gentity_s {
entityState_ts;// communicated by server to clients
entityShared_tr;// shared by both the server system and game
// DO NOT MODIFY ANYTHING ABOVE THIS, THE SERVER
// EXPECTS THE FIELDS IN THAT ORDER!
//================================
struct gclient_s*client;// NULL if not a client
[Code] ....
This whole entity is passed to the engine at runtime, but only the first two fields are declared for the engine:
Code:
// the server looks at a sharedEntity, which is the start of the game's gentity_t structure
typedef struct {
entityState_ts;// communicated by server to clients
entityShared_tr;// shared by both the server system and game
} sharedEntity_t;
My problem is that I need to access the health field of gentity_t from the engine. Technically, this is possible, but the health field is not declared in sharedEntity (which is the same memory address than gentity_t in the gamecode), so this is not straightforward.
I am looking for an elegant way to do this, and my constraint is that I must not edit the gamecode, only the engine.
The solutions I've thought:
- Just copy the whole gentity_t fields into sharedEntity_t. This would work I think but would be redundant, and I would like to avoid copying this huge set of fields.
- Include the two headers files declaring the gentity_t and sharedEntity_t structs, and create a Getter and a Setter functions that would cast a gentity_t over a sharedEntity_t and return/set a field. The problem is that I can't simply include them because they are both including some common headers files and this produce a recursive include error (and I can't modify the files to add a check, these are normally in the gamecode).
- Directly access the health field using a clever memory pointer, but I don't even know if that's possible given the huge number of fields prior health with many different types?
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Jun 12, 2013
I’m developing an application where I have some defines, like:
#define PatientName “(0x0010, 0x0010)”
#define PatientId “(0x0010, 0x0020)”
#define Modality “(0x0010, 0x0030)”
And a few more (up to 3000). These defines are used to read certain fields from a DICOM image, that give information about that image (Patient Name, etc…). However I don’t wish to read all these fields. Instead I’m trying to load an .ini configuration which will configure which fields to read. For example:
[PROPERTIES]
# Fields to read
fields=PatienId,Modality
This would only retrieve the Patient Name and a Modality.
The problem is, the values I retrieve from the .ini file (reading and parsing the file with std::fstream) come as a string. How could I retrieve, for example, the defined value from PatientId, i.e. “(0x0010, 0x0020)”? Something like std::cout << # << "PatientId"; won't work.
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Jan 21, 2014
So I'm rewriting an old project of mine, and I'm trying to determine if there's truly any better way to map the data taken from a text file "dictionary" into the correct class fields for further processing. For example:
FNAME=MY_FIRST_NAME
ADDR=123 SOMEWHERE LN, NOWHERESVILLE, TX 01234
LNAME=MY_LAST_NAME
TOTCALLS=47
In each of these, I'd need the "value" (MY_FIRST_NAME, MY_LAST_NAME, etc) from the "keys" (FNAME, LNAME, etc) to be mapped to the proper class fields. Say, for example, I had this:
Class DataProcessing {
public string Address;
public string FirstName;
public string LastName;
public int TotalCalls;
...
}
I would need DataProcessing.Address to be set to the value in the ADDR key/value pair. The same would be true for each other field. The problem is that based on the text file's source (which isn't under my control, and won't be changed anytime soon), the key/value pairs are not always in the same place...so a second file could have the data as such:
TOTCALLS=47
ADDR=123 SOMEWHERE LN, NOWHERESVILLE, TX 01234
LNAME=DARKPOETCC'S LAST NAME
FNAME=DARKPOETCC'S FIRST NAME
Any smarter way to do this than looping through each line that was read in from the file, and determining where it belongs, such as (pseudo code follows):
IF FieldName == "TOTCALLS" THEN
//Assign to TotalCalls field
ELSEIF FieldName == "ADDR" THEN
//Assign to Address field
ELSEIF FieldName == (You get the picture...)
//Do thing N_Field
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Aug 19, 2013
I want to search and display the field stored in text file and also i want to delete the field that is entered. Case 3 and 4 is incomplete.
#include<iostream>
#include<fstream>
#include<string>
using namespace std;
int main() {
int a;
int st_id;
[Code] ....
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Oct 21, 2014
Goal: Use a struct that has 4 fields, input to those fields, and pass to function to display.
Problem: (38) : error C2365: 'displaySData' : redefinition; previous definition was 'data variable'
Code:
#include <iostream>
#include <string>
using namespace std;
//prototypes
void displaySData(MovieData, MovieData);
[Code] .....
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Mar 16, 2013
will copy constructor does object initialization using another already created object? I understand that it can be applied for object initialization and not for assignment.Is it correct?
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Jul 3, 2014
I have a method to take a Tile object and make an instances of it based on some data from the original object. Than it is suppose to manipulate the a specific instance and save the results. The first loop through it works but it changes all instance as well as the base.
public static int recurse(int count, Tile[,] b,Huristic h,int check) {
if (check==1) {
boardState.Add(B)/>;
return check;
} if (check == 0)
[Code] .....
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Dec 13, 2012
#include "B.h"
class A {
public :
A()
{
s_b = new B();
b = new B();
[Code] ....
In my project i have seen static object as above . But not able to know what is the exact use of it and how they are different from general object .
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Sep 11, 2014
a function returns a temporary object like
int myfun(){
int x = 0;
return x;
}
this function will return a temporary integer now void fun1(const int & num); this function can receive from myfun().BUT void fun2(int & num); this function cannot receive from myfun() Why is that, Moreover what is lifetime of a temporary object like one returned in myfun() ???
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Mar 28, 2014
I am trying to use web api in order to return custom json response keys. For this i have return a custom class to return json response
Custom Class:
using System;
using System.Collections.Generic;
using System.Globalization;
using System.Linq;
[Code].....
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