C++ :: How To Put File Data Into Members Of A Class - Array Transferring
Mar 10, 2013
I'm trying to put file data into members of a class. Remember to type in the file name you want to open. Cool feature right? I just had Dbase.txt so I chose that.
Fixed stuff in the .txt. Now I need to figure out why it only does 1 set and then ends.
#include <cstdio>
#include <cstdlib>
#include <iostream>
#include <fstream>
using namespace std;
class INFO {
[Code] .....
Dbase.txt:
Bob
Guy
Programmer
M
9999.99
40
------------------
Little
Guy
Little Brother
M
0.0
3
------------------
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Feb 11, 2013
I have some problem with the ssize_t sendfile function.
ssize_t sendfile(int out_fd, int in_fd, off_t *offset, size_t count);
The error:
Lesson_4_1A_Home_work.c:84:24: error: expected declaration specifiers or ‘...’ before string constant
Lesson_4_1A_Home_work.c:84:37: error: expected declaration specifiers or ‘...’ before string constant
Lesson_4_1A_Home_work.c:84:63: error: expected declaration specifiers or ‘...’ before ‘strlen’
Code:
#ifdef HAVE_CONFIG_H
#include <config.h>
#endif
#include <sys/sendfile.h>
#include <sys/types.h>
[Code]....
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Feb 22, 2015
I can not do transferring data to textboxes from database.
="c#">using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using MySql.Data.MySqlClient;
namespace WindowsFormsApplication1{
[code]....
I got the error this line:
read = cmd.ExecuteReader();
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Apr 16, 2014
The program is supposed to read a formatted .txt file and store the data into their respective [Class] Members. It will then output the data collected onto screen.I overloaded ifstream and istream. When I call for file>>ptr[i] to read the data, something goes wrong. It prompts me to input data (which is in istream overload).The Data in .txt file is as follows;
#ifndef STUDENTTESTSCORES_H
#define STUDENTTESTSCORES_H
#include <string>
#include <iostream>
#include <fstream>
using namespace std;
[code]....
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Nov 4, 2014
Is it generally better to initialize string data members as nullptr or as a zero-size array?
I can understand the former is superior from a memory-use perspective and also not requiring the extra allocation step. However, many string management functions will throw an exception - wcslen for instance - if you pass them a null pointer. Therefore I am finding any performance gained is somewhat wiped out by the extra if(pstString==nullptr) guards I have to use where it is possible a wchar_* may still be at null when the function is called.
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Apr 15, 2013
If I have an array of some class, and that class has const members, is there some way I can call a custom constructor on elements of the array?
I can't seem to reinitialize an element in foos in the example below. A thread on stack overflow mentioned the copy constructor show allow it, but I get "no match for call to '(Foo) (Foo&)'" when I try it.
Code:
class Foo {
public:
Foo();
Foo(int x, int y);
[Code] .....
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Apr 17, 2013
From my book:
"A static function might have this prototype:
static void Afunction(int n);
A static function can be called in relation to a particular object by a statement such as the following:
aBox.Afunction(10);
The function has no access to the non-static members of aBox. The same function could also be called without reference to an object. In this case, the statement would be:
CBox::Afunction(10);
where CBox is the class name. Using the class name and the scope resolution operator tells the compiler to which class Afunction() belongs."
Why exactly cant Afunction access non-static members?
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Feb 1, 2014
In the function *expandArrayList and *trimArrayList I need to allocate either more memory or less memory to the given array. Right now I am using malloc on a new array and then transferring the elements of the original array to the new array, freeing the original array, and then reassigning it to the new array so it's size and capacity are either bigger or smaller than the original. I feel like there has to be a simpler way to do this with either realloc or calloc, but I cant find sufficient information on either online. Would I be able to use either to make this easier and the code cleaner?
Also, these are character arrays that contain several character arrays inside them, so I was wondering what the best way to transfer the contents of one array to the other would be. I have gone between
Code:
//example
for (i=0; i<length; i++){
newarray[i] = oldarray[i];
}
and
Code: for (i=0; i<length; i++){
strcpy(newarray[i], oldarray[i]);
}
but I'm not sure which one (if either) should work.
The 'ArrayList.h' file that is included contains the structure ArrayList, as well as the function prototypes for the functions listed below.
Here is the structure in ArrayList.h:
Code:
#define DEFAULT_INIT_LEN 10
typedef struct ArrayList {
// We will store an array of strings (i.e., an array of char arrays)
char **array;
[Code] ....
Here is my code:
Code:
//included libraries
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "ArrayList.h"
//Create arraylist
[Code]....
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Jul 15, 2014
I would like to know if there's a way to make a method from a derived class a friend of its base class. Something like:
class Derived;
class Base {
int i, j;
friend void Derived::f();
protected:
Base();
[Code] ......
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Jun 28, 2013
I am new to c++ programming and i have written a simple class program to display the name and duration of the project
#include<iostream>
class project {
public:
std::string name;
int duration;
};
[Code] ....
Now i am trying to the write the same program with the usage of member functions using set and get member functions. i have tried the following
#include<iostream.h>
class project {
std::string name;
int duration;
// Member functions declaration
[Code] ....
I am not sure whether above code logic is correct, how to proceed with it.
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Sep 16, 2013
I want to define a class, which will have two members, for example, vaporPressureStatus and vaporPressure
enum vpStatus_t {nonesense, unknown, known, saturated};
class pore_t {
public:
vpStatus_t vpStatus;
double vaporPressure;
};
when vpStatus is nonsense and unknown, the vaporPressure should not have a value; and if I calculate out a value for vaporPressure, the vpStatus can be set as known.
I am wondering if there is any set, pair or other structure can hold this two members together, so that when I change one's value, the other guy will also change accordingly.
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Nov 12, 2013
How does an object access its private data members in copy constructor.
The relevant part of the code: Code: C::C(const C &obj)
{
x = obj.x;
y = obj.y;
}
Normally the object1 called "obj" cannot access its private data members outside. But in this situation it can access. How can it be explained?
Here are the complete code:
Code:
#include <iostream>
using namespace std;
class C{
public:
C(int,int);
C(const C &);
[Code] .....
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Jun 24, 2014
I've been creating an API and I'm now stuck on callbacks. There are many APIs that allow callbacks to class members(e.g. Windows API) using a void pointer to the object. I've searched the internet for hours and I can't find one example of how to use the "hidden object parameter" of an class method pointer that doesn't use std::function/bind or boost::function/bind. Any information on how API's like Windows API are able to use class methods as callbacks
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Apr 14, 2013
The reason that class members are private by default is because, in general, an object of a class should be a self-contained entity such that the data that make the object what it is should be encapsulated and only changed under controlled circumstances. Public data members should be very much the exception. As you’ll see a little later in the chapter, though, it’s also possible to place other restrictions on the accessibility of members of a class.
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Jul 12, 2013
It's hard to give a precise title but here is the question in detail: I have a class, something like this:
Code:
class classA{
public:
void fnA();
...
};
and another class that contains objects of classA:
Code:
class classB{
public:
classA A1;
classA A2;
classA A3;
vector<classA*> vA;
...
};
classB B1;
Now is it possible to access B1.vA from B1.A1.fnA() through some kind of pointer chain like this->parent->vA ? If so
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Mar 6, 2014
Overview of problem : I am using std::vector to hold objects of Subject. Now this vector contains lots of objects( with lots I mean 10-20 objects at max) . These objects have string member values like category and sub_category. Both category and sub_category can have string which can be same of other objects's sub_category & category.
Issue: Now I want my std::vector to have only those objects whose's sub_category are unique. If category is not unique that's not a problem .
Secondly if we found 2 objects having same sub_category then we have to delete one of them from the vector. we will delete it based on some rules example
Rules for deleting are if
i) instance of Subject ->category = " Land " OR if category = "Jungle" then delete other duplicate object ,
ii) if above condition doesn't match then delete either of them.
I am wondering , how would I compare the sub-items from the vector . For example. I have class say Subject
class Subject {
public :
// some constructors,
// functions to get ., set category and sub category
std::String get_sub_category()
std::string get_category();
private:
std::string category;
std::string sub_category;
}
I have vector which stores object of Subjects. Example : vector<Subject> copy_vector;
Now what I want is to delete the object from vector that has same sub_category I am not looking for source code buT i need a starting point,? Example:
copy_vector[0] = Animal object that has sub_category Tiger
copy_vector [1] = Animal object with Lion as sub category
copy_vector[2] = Forest object with sub_category Tiger
What I want is to based on some conditions(which I can do ) remove either Forest or Animal object containing Tiger. But for that how would I do comparison? I have written the function and have checked it.
std::vector< Subject >copy_vector;
// copy_vector contains all the objects of Subject with redundant sub_category
for( std::vector< Subject >::iterator ii = copy_vector.begin() ; ii != copy_vector.end() ; ++ii ) {
sub_category = ii->get_sub_category();
[code] ....
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May 24, 2014
All the undos and redos were working fine until the pointer data members came into the picture. The problem is that the values pointed to changed, but the pointers themselves did not. So restoring gives the same pointers but they still point to the new values. I think the solution is that the classes that are the pointer data members themselves need their own Mementos (which would be a lot of work because there are many data member pointers in my program). Is that the only approach?
Here is a sample code to show what I'm talking about. You can compile and run the program to see the problem it has restoring values of pointer data members:
#include <iostream>
#include <string>
#include <memory>
#include <vector>
#include <list>
#include <cstdlib>
#include <ctime>
class FoodHistory {
[Code] ....
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Jun 26, 2012
I am to first increment data members of object that has not created dynamically (i have done with this part),now i have created object dynamically and how to increment its data which i have passed as argument as:
obj3 = new manage(35 , 36)
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Jan 10, 2013
Let's say I have the following class:
class MyClass {
private:
int m_myInt;
public:
int myInt() {return this->m_myInt;};
int myFunc();
};
Which of the following is to prefer;
int MyClass::myFunc() {
return 2*this->m_myInt;
}
or
int MyClass::myFunc() {
return 2*this->myInt();
}
The second one seems better? Are both OK? What's the best practice?
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Jan 17, 2013
I have a little problem with template classes and their specialization. Here is a short example:
template <typename T>
struct A{
// some typedefs
[Code]....
The above example is not compiling, because of the assignment of the const static double. Double needs a constructor, but that doesn't work (or seems not to work) with static.
I'm not sure, if it works at all in C++ that way. All I want is a template struct with some typedefs and a constant which is different for different specializations. Don't think it has to be static, but that would be better style, wouldn't it?
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Oct 22, 2014
I am doing C++ data structures exercises, and I am still learning some of the more basic concepts. I have a parent class:
template<class T>
class linkedListType {
public:
protected:
int count;
nodeType<T> *first;
nodeType<T> *last;
private:
};
Derived class:
#include "linkedListType.h"
template<class T>
class orderedLinkedList: public linkedListType<T> {
public:
void mergeList(orderedLinkedList<T> &list1, orderedLinkedList<t> &list2) {
first = list1.first;
...
} private:
};
There is more code in my mergeList() function, but I included the line that is giving me problems. The error that my CodeBlocks compiler is giving me is that 'first' was not declared in this scope.
Strangely enough, if I change it to this->first, the error disappears.
1. Why does it not recognise 'first'?
2. Why would this->first work at all? Is the 'this' object a smart pointer?
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Nov 17, 2014
Im trying to make a c++ program for a school project, and i need to store the information into binary files, but I'm having some problems trying to store a class with string members, for example:
class whatever{
protected:
string name;
public:
(List of functions)
}
But if I do that, my code just dont work when I write and read a binary file, but if I change the string to char array, for example:
class whatever{
protected:
char name[20];
public:
(List of functions)
}
It works good, so I wanted to know if there's some way to store a class wiht strings in binary files, or what am I doing wrong?
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Oct 15, 2013
How I can implement it.
Tickable.h
#include <list>
#ifdef TICKABLE_EXPORTS //Automatically defined by MSVS
#define DLL __declspec(dllexport)
#else
#define DLL __declspec(dllimport)
#pragma comment(lib, "Tickable.lib")
#endif
class DLL Tickable{
[Code] ....
error LNK2001:
unresolved external symbol "private: static class std::list<class Tickable*,SKIPPED BITS> Tickable::subs" HUGE_SYMBOL_LIST
PATHTickable.obj
I know with such a tiny and insignificant class the dll export seems pointless but this class is actually intended to be a .lib ONLY. But it is derived from by .dll style classes, and through inheritance this error is the exact same as what appears in the derived class, I just imagine that the cut down version would be easier to work with.
Is it possible to hold either a static variable in a dll which is of a dynamic type, OR would it be possible to reference an external variable which is static throughout the instances and this variable can be chucked away in a namespace of mine somewhere?
I suppose my only other option (if this is possible) would be to define a maximum instance number and create a standard array of pointers but this could both waste so much memory when not in use and cause problems if I need more memory.
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May 18, 2013
"A nested class has free access to all the static members of the enclosing class. All the instance members can be accessed through an object of the enclosing class type, or a pointer or reference to an object."
How can the members be accessed through an object of the enclosing class type? I understand the pointer and reference part because for them you dont need the full definition, but for creating a object you do?
Also it has free access to all static members because the nested class is part of the enclosed class and with static it exists in everything inside the enclosing class? Right or am I missing something?
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Mar 28, 2015
#include <iostream>
#include <fstream>
using namespace std;
int main() {
int r = 0;
int c = 0;
int num[17][15] = { 0 };
[Code] ...
// Here is my code for displaying the data from the text file into a 2d array and height next to it, but I am not able to diaplay the height from 60 to 76 next to the row of the 2d array, as shown in the table below. This is my program:
Recently the health authorities have listed a new way to calculate the body mass index (BMI) of an individual.
Values of 20 – 24 are classified as normal, 25-29 as overweight, and 30-34 as heavy.
The table below is a portion of a typical BMI table.
BMI:202122232425262728293031323334
Height:
60102108113118123128133138143149154159164169174
61106111116122127132138143148153159164169175180
.
.
.
MY task is to write a program that does the following things:
1.Produce the table by reading in the data from bmi.txt (on Moodle) into a 2-D array.
2. Display the table neatly on the screen, with row and column headings. The BMI should go from 20 to 34. The height should go from 60 to 76 inches.
3. Prompt the use for their height (in inches) and their weight.
4. Make the program print the closest BMI.
If their weight is lower than the values on the table, use 20 as the BMI.
If their weight is higher than the values on the table, use 34 as the BMI.
5.Loop the program so the user can find more BMI’s.
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Oct 18, 2014
I am having trouble putting data from a txt file onto a vector of a class. For instance.
class employee{
setname(string) {
some code
} getname () {
some code
} setid(int)
[Code] ....
How would use my setname function in my class using my vector? I tried doing vec[num].setname(tempname) but it doesn't work. I know it does not work because I have to use .push back for a vector but I don't know exactly how to pushback using the set name function call.
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