C :: Bitfield Array - Using Standard Technique Of Creating A Structure Within Union

Mar 27, 2013

Any way that one could create a bitfield using the standard technique of creating a structure within a union, as follows:

Code:
typedef union {
struct {
unsigned b0 : 1;
unsigned b1 : 1;
:
:
unsigned b(n-1) : 1;
} bits;
unsigned int value;
}

BIT_FIELD_TYPE; Except, what I'd like to do is to replace all the single-bit elements in the bits structure with a single statement that creates an array of, say, 32 values. The clear advantage of this is that it could be traversed using an iterator, ...

Code:
main() {
BIT_FIELD_TYPE foo;
unsigned int i;
...
for (i = 0; i < n; i++) {
... (print out foo.bits.b[i]) ...
}

So far, I've not figured out a way to do it, either as an array, or using a pointer to iterate through the individual bits.

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C :: Using Structure In Union

May 27, 2013

I'm trying to use a structure in union in the following format:

Code:
union data
{
unsigned char All[10] ;
struct data_pkt
{
unsigned char ack;
unsigned short status;
unsigned short data_length;
unsigned char Data[5];
}format;
}adb; adb.

All has 10 bytes which is equivalent to the structure bytes. ie 6 bytes if unsigned char and 2 short i.e 4 bytes. Thus total 10 bytes is given to adb.All. When I print the struct size I get 12 bytes. This creates problem in obtaining data in union. According to the program:

adb.format.ack should have the address of adb.All[0]
adb.format.status should have the address of adb.All[1]
adb.format.data_length should have the address of adb.All[3]
adb.format.Data[0] should have the address of adb.All[5]

But in actual case this is how memory is allocated:

adb.format.ack assigned to the address of adb.All[0]
adb.format.status assigned to the address of adb.All[2]
adb.format.data_length assigned to the address of adb.All[4]
adb.format.Data[0] assigned to the address of adb.All[6]

Why this is happening? How can I solve this?

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C++ :: Malloc For Union Inside Structure Fails

Dec 27, 2012

I have some problem while allocating memory to a union inside structure. Below is the code i am using

ON SYSTEM1:

This works fine

ON SYSTEM2:

compiler complains saying "need structure or union type" while allocating MYSTRUCT1.

If I change:

shreyas[0].UnionAttr.struct1 = (MYSTRUCT1 *) malloc (sizeof(MYSTRUCT1)
to
shreyas[0].UnionAttr->struct1 = (MYSTRUCT1 *) malloc (sizeof(MYSTRUCT1)

This compiler on SYSTEM2 is happy. but second way does not look correct to me and compiler on system 1 complains about it. Which is the correct way to allocate memory?

If first one is correct then what should i look in for to avoid this error? Could this be an issue with compiler on SYSTEM2? If i use second method on SYSTEM2 code segfaults during malloc.

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
typedef struct mystruct1 {
int a;
int b;

[Code] ....

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C++ :: Splitting RGBA Into Individual Bytes By Creating Union

Jan 16, 2013

I am currently working with win32 API , for image processing, one of the windows function returns RGBA ( colors ) as unsigned int , I then split it into individual bytes by creating a union ,

Code:
union colour {
unsigned int value;
unsigned char RGBA[4];
}

to spit the int into individual bytes, my Question is there a better or my convenient way of doing this.

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C++ :: Creating List Of Medical Resources And Their Attributes - Input To Structure Array Not Working?

Mar 23, 2014

I wrote this program to create a list of medical resources and their attributes, a task I have been performing repeatedly lately. I'm still fairly new to C++, so I thought to create a structure "Resource", and then an array of those structures "city[300]". My problem is that the input doesn't seem to be happening: the program runs, but when it prints to screen/writes to the file at the end, all the shows is:

Resource Type:
Name:
Address:
Phone:
Website:

for every resource that was input. All the fields are blank.

#include <iostream>
#include <fstream>
#include <string>
using namespace std;
struct Resource {
string typeID;
string name;

[Code] ....

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C :: Make A Hash Table Array Of Linked Lists / Separate Chaining Technique

Jul 5, 2013

how to create a hash table array and use linked lists inside the elements.

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C++ :: Creating Tree Like Structure Using Linked List

Apr 25, 2014

How would I go about creating a tree like structure using linked lists, I am thinking of making a rubix cube solver program, what I want to do create nodes that each do one operation like turn left, right, up, down but I dont know how to go about starting this.

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C++ :: Finding The Address Of A Bitfield

Aug 14, 2013

So I obviously can't take the address of a bitfield, but is there a way to get the address of the field holding the bitfield? What I'm trying to do is find the address of the parent field of a bitfield in a class. For example

Code:
class Foo
{
public:
int a;
int b : 4;
int c : 28;
[Code] ....

My goal is to get the offset address of the int storing c in class Foo. But offsetof uses the address of c, so I get a compile error since c is a bitfield. What I wanted as output from the above would be "4", since an int is 4 bytes (on my system). So the int holding both b & c starts 4 bytes from the start of the Foo class. Is there any way to do this in c/c++?

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C++ :: Initializing A POD Bitfield Struct?

Apr 14, 2014

I'm wondering what is the "best" way to initialize a bitfield struct. I have this bitfield, defined as:

Code:
struct S
{
unsigned int a : 1;
unsigned int b : 1;
};

If I'm "using" the bitfield, I can initialize it easily when declaring it, as so:

Code:
int main()
{
S s = {0};
}

Now, the issue I'm facing is that I want to embed S inside another struct, which I'll name "outer". EG:

Code:
struct Outer
{
S s;
};

I'm wondering what the "best" way to have Outer initialize S is? I've seen a lot of people use the "union" approach:

Code:
struct Outer
{
Outer()
{
u.all = 0;
}
union
{
unsigned char all;
S s;
} u;
};

but:This adds an extra field depth (the union's u)Does bit hacking, in a way (is the bitfield as large as my field?) I'd have wanted to initialize the field in my constructor, as so:

Code:
Outer::Outer() : s({0})

However, this would appear to be a C++11 feature only.

I have, however, "observed" that by simply "empty constructing" s, eg:

Code:
Outer::Outer() : s(){} //Initialize s ?
vs
Outer::Outer(){}

Then my bitfield "appears" initialized.

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C/C++ :: How To Pad Characters In RSA Cryptography Technique

Oct 7, 2014

How to pad characters in rsa algortihm.eg 'H' becomes 45 so how to do it so that i can use that in my equation.

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Visual C++ :: Search Technique On DNA Sequence

May 10, 2013

Given a set of DNA string. Find minimum length string S so that, given DNA strings are subsequence of S.

For example, if given set of string is: {CAGT, ATGC, CGTT, ACGT, AATT} then answer is: 8. Because, ACAGTGCT contains all given DNA as subsequence.

Given n such DNA string (n <= 8), each of length atmost 5. Find out the least length.

Sample:
5
AATT
CGTT
CAGT
ACGT
ATGC

Output:
8

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C++ :: Read 100 Elements From Standard Input Device And Store Them In Array

Feb 19, 2014

Write code to do the following:

1) declare a variable ptr as a pointer to int and initialize it to NULL
2) dynamically allocate memory for an array of 100 elements
3) read 100 elements from the standard input device and store them in the array.

This is what I have so far, I'd like to know if its ok or if something is wrong.

int *ptr = NULL;
ptr = new int[100];
cin >> dataPtr [arr];

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C++ :: Why Can Initialize Array Nested In Structure Like Array

Feb 7, 2015

Example :
Code:
struct x {
int v[4];
};
const x test = { 0, 1, 2, 3 };

Why can I do this? How does the compiler know to write to this in the proper way? I get that v would be contiguous. Does that have something to do with it?

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C++ :: Using Union For Combining Registers

Nov 16, 2013

How I could use unions to combine registers elegantly. For example I have the 8 bit registers B and C & I have opcodes that work on each independent register such as add b, c, which is simple, but then I also have opcodes that work on both of them as if they're one like ld a, bc. I know I could go about that by just masking them together but I've seen it done with unions before & it made everything so much more simple.

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C++ :: Using Pointer In Union And Assigning Value

Jul 2, 2013

In the current code,We are using pointer of union and assigning value.

class sample {
union {
short *two_int;
int *four_int;
double *eight_real;
char *one_ascii;
// void *v;
}; }

Than we assign value in following way.

sample.four_int[0] = (x + xoff); ( x and xoff and y and yoff all are integer)
sample.four_int[1] = (y + yoff);

Than we write data into file. it was working fine into 32 bit machine but it is not working 64bit machine. When I compare data and found that data is divided by 4. For Ex The File generating from 32 bit machine contain 80 than 64 bit . File contain 20.

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C++ :: Changes In Union Typedef Not Mirrored

Sep 1, 2013

I have made VGA emulation with registers and memory in my emulator. But for some reason the writes to the union array with CPU data (register 0-8 of the VGA's Graphics Controller Registers, referenced with <GRAPHREGS>.DATA[index]) don't reflect on the union's data.

typedef union __attribute__((packed)) {
byte DATA[9]; //9 registers present!
struct //Contains the registers itself! {
//Set/Reset Register (index 00h)
union {

[code]...

what's going wrong? Have I made an error in the registers?

(In this case I write to register <GRAPHREGS>.DATA[8] (which should be the <GRAPHREGS>.REGISTERS.BITMASKREGISTER)), but the BITMASKREGISTER stays 0, while DATA[8] gets the correct value.

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C++ :: Assigning Values To Union?

Sep 10, 2012

I have the following C++ code

typedef union UUID {
unsigned char byte[16]; /**< Array of 16 bytes. */
unsigned int ll[2]; /**< Array of two 64-bit words. */
} UUID;

[Code] ......

The compiler complains thus

$ g++ union.cpp
union.cpp: In function "int main()":
union.cpp:15:17: warning: extended initializer lists only available with -std=c++0x or -std=gnu++0x
union.cpp:15:17: warning: extended initializer lists only available with -std=c++0x or -std=gnu++0x
union.cpp:15:17: error: no match for "operator=" in "entry.EntryHeader::uuid = {0, 0, 0, 2}"
union.cpp:1:20: note: candidate is: UUID& UUID:perator=(const UUID&)

How do I go about assigning values to this union in C++.

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C++ :: Classes Defined With Struct And Union

Mar 12, 2013

Classes defined with struct and union

Classes can be defined not only with keyword class, but also with keywords struct and union.

The concepts of class and data structure are so similar that both keywords (struct and class) can be used in C++ to declare classes (i.e. structs can also have function members in C++, not only data members). The only difference between both is that members of classes declared with the keyword struct have public access by default, while members of classes declared with the keyword class have private access. For all other purposes both keywords are equivalent.

The concept of unions is different from that of classes declared with struct and class, since unions only store one data member at a time, but nevertheless they are also classes and can thus also hold function members. The default access in union classes is public.

The above is a statement taken from a C++ tutorial. So I understand classes a bit better now but the above quote doesnt make too much sense. Is it saying that you can have a class within a class?

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C :: Under-allocating Memory For A Tagged Union

Mar 6, 2015

What i'm interested in is the behavour of a struct/union constructed like this:

Code:
typedef struct {
uint64_t num1;
uint64_t num2;
} st_a;

typedef struct {
uint64_t num1;
uint32_t num2;

[Code] .....

What kind of behavour could I expect from object, in the following cases:

1. newsomestruct(0)->u.a.num1 = 2;
2. newsomestruct(1)->u.b.num1 = 2;
3. newsomestruct(0)->u.a.num2 = 2;
4. newsomestruct(1)->u.b.num2 = 2;
5. newsomestruct(0)->u.b.num1 = 2;
6. newsomestruct(1)->u.a.num1 = 2;
7. newsomestruct(0)->u.b.num2 = 2;
8. newsomestruct(1)->u.a.num2 = 2;
9. Code:

somestruct* ss1 = newsomestruct(0);
somestruct* ss2 = newsomestruct(1);
* ss1 = * ss2; 10. Code: somestruct* ss1 = newsomestruct(0);
somestruct* ss2 = newsomestruct(1);
* ss2 = * ss1;

This is what I'd expect, but I can't find any evidence online in C standards or elsewhere:

1. Works as expected, sets the value of a.num1 to 2.
2. Works as expected, sets the value of b.num1 to 2.
3. Works as expected, sets the value of a.num2 to 2.
4. Works as expected, sets the value of b.num2 to 2.
5. Works as expected, sets the value of b.num1 to 2.
6. Works as expected, sets the value of a.num1 to 2.
7. Works as expected, sets the value of b.num1 to 2.
8. Crashes/Memory Corruption, attempted to alter memory outside struct.
9. Works as expected, * ss1 == * ss2
10. Crashes/Memory Corruption, attempted to alter memory outside struct.

I've tested simular code on my machine (Xubuntu 14.04LTS compiled with gcc on -O3) and it appears to be reliable, given that you stick with acessing the type tagged in the struct or the common initial union struct members (in this case num1).

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C++ :: Pointer Of Union And Fwrite Operation

Jul 5, 2013

I have union of pointer.

union {
short *two_int;
int *four_int;
double *eight_real;
char *one_ascii;
// void *v;
};

We have write function which write into file.

fwrite (r.one_ascii, 1, i, outstr);

I found one thing,When we write function, we fill only four int in following way.

r.four_int[0] = x + xoff;
r.four_int[1] = y + yoff;

So my question,we fill four_int but write one_ascii only.As is it union of pointer. So it does not matter. I am using 64bit machine and do not have any issue in 32 bit machine.

For more information: [URL] ....

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C++ :: How To Find Out Which Member Of Union Is Currently Set / Active

Jan 16, 2015

how to find out which member of union is currently set/active.

exm:
union myunion{
int i;
float f;
}

if i set myunion ob{7}, it set ob.i=7;

my q? is how to find out i is set f is not set/ not acrive

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C++ :: How To Program Boolean Union And Intersection

Jun 19, 2014

It involves some discrete mathematics. Any code snippet to get me started?

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C :: Set Every Array Value In Structure To Zero

Nov 22, 2013

i'd like to ask if it's possible to fill every array in structure to zero. (Without using too much cycles)Something like this (I know that it doesn't work):

Code:

typedef struct {
char name[30], sname[30], adress[30], day, month; int year; char number[9], email[30];
} person;
void create_list(person z[100])
}

[code]....

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C++ :: Find Intersection / Union And Difference Of Two Sets

Feb 17, 2014

The program is to find intersection,union and difference of two sets. The program take the input correctly but after it crashes with the message that some exe is not working...

Code:
#include<iostream>
using namespace std;
void Input(int *A, int*B, int size1, int size2)
//input function {

[Code] ....

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C++ :: Union Of Two Vector ADT Bags - Operator Overload

Apr 30, 2014

I'm trying to come up with the union of two Vector ADT bags, so I have to overload the '+' operator, but I'm getting a bunch of error messages saying:

VectorBag.cpp: In instantiation of ‘VectorBag<ItemType> VectorBag<ItemType>::operator+(VectorBag<ItemType>) [with ItemType = int]’:
proj2.cpp:161:42: required from here
VectorBag.cpp:81:24: error: no match for ‘operator[]’ (operand types are ‘VectorBag<int>’ and ‘int’)
newBag.add(anotherBag[i]);
^
Here is the function to overload the operator:

template<class ItemType>
VectorBag<ItemType>
VectorBag<ItemType>::operator+(VectorBag<ItemType> anotherBag) {
VectorBag<ItemType> newBag;
for (int i = 0; i < anotherBag.getCurrentSize(); i++)
newBag.add(anotherBag[i]);
}

The add() function is pre-defined by me somewhere else in the code. It basically does push_back().

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C# :: T-SQL Multi Table Union To Call Out Data

Jul 15, 2014

I'm trying to union eleven tables to call out data. Parent table is 'Events', child tables are 'SR1Laptimes', 'SR2Laptimes' and so on (there are ten SR... tables). Primary key in all tables is EventName. Parent/Child relationship is Events.EventName/SR1Laptimes.EventName etc All tables that start with SR have the same Schema. I'm trying to call out MIN(Q1) across all table but first need to Union them I believe. Here is my code.

myCommand.CommandText = "SELECT MIN(Q1), MIN(Q2), MIN(Q3), MIN(Q4), MIN(LaptimesMinutes), MIN(LaptimesSeconds) FROM (SELECT * FROM Events UNION ALL SELECT * FROM SR1Laptimes UNION ALL SELECT * FROM SR2Laptimes) WHERE (Events.Track = @track) AND (Events.Number = @number) AND (Events.Rider = @rider)";
myCommand.Parameters.AddWithValue("@track", analysisTrackComboBox.Text);
myCommand.Parameters.AddWithValue("@number", analysisNumberComboBox.Text);
myCommand.Parameters.AddWithValue("@rider", analysisRiderComboBox.Text);

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