I want to build a server which holds hundreds of thousands of active users in memory. To keep all the users organized i would like to store them in a Vector.
The problem is how i could quickly and easy find the object whenever i need it? All users will have a unique ID. Would it be possible to keep some form of a Vector Index on the unique id number?
Here is the code,
vector<int> v;
v.push_back(4);
v.push_back(11);
v.push_back(34);
v.push_back(5);
v.push_back(14);
v.push_back(32);
vector<int>::iterator next;
[Code] ....
I got a debug assertion error. What might be wrong?
I am creating a menu-driven program which creates a small database using a binary search tree. I am having issues with the last method I need for the program. The way it is coded now only gives me blank data when I print it. Here is the exact wording for the requirements for this method:
"Output a complete report to the text file named BillionaireReports.txt in increasing order by billionaire rank, that contains all data fro each record stored in the BST. Note: this is not a simple traversal. You may assume that the rank is never less than 1 and never greater that 500. Do NOT copy the data into another BST, into an array, into a linked list, or into any other type of data structure. Retrieve the data directly from the binary search tree which is stored in order by name."
Here is the method in question:
void BillionaireDatabase::displayRankReport() {
int i = 1;
for(i; i <=500; i++) {
billionaireDatabaseBST.contains(Billionaire& anItem);
[Code] ....
I know how to sort the database by the key, but I'm not sure how to sort by something that is not the key.
Here are the functions I have available via the BST (these were written by the professor)
//------------------------------------------------------------
// Constructor and Destructor Section.
//------------------------------------------------------------
BinarySearchTree();
BinarySearchTree(const ItemType& rootItem);
BinarySearchTree(const BinarySearchTree<ItemType>& tree);
virtual ~BinarySearchTree();
[Code] ....
I will try my best to describe this problem I am having because I am not sure if I can reproduce the error in a small code example as this is part of a large code project.
I have a plain std::vector which contains pointers to objects.
When attempting to delete the objects, even if I know for a fact that the std::vector has at least one object in it as shown by the debugger, I get the "Vector Subscript Out of Range" error.
I'll even do a range for loop like so:
for (auto & e : CurrentObjects) {
delete e;
}
And yet I still get the "Vector Subscript Out of Range" error. The destructor is never called for the object represented by "e" so I am not sure why I get the error.
I have asked a related question before, and it was resolved successfully. In the past, when I wanted to use std::max_element in order to find the maximum element (or even sort by using std::sort) of a vector of structures according to one of the members of the structure, all I had to do was to insert a specially designed comparison function as the third argument of the function std::max::element. But the latter comparison function naturally accepts two arguments internally.
For instance, here is a test program that successfully finds the maximum according to just one member of the structure:
Code:
#include <iostream>
#include <string>
#include <vector>
#include <algorithm>
[Code] ....
And the output was this, as expected:
Maximum element S.a of vector<S> vec is at: 9
[I]max element of vec.a between slot 3 and slot 6 is: 6, and its index is: 6 vec[6].a = 6
[I]max element of vec.a between slot 4 and slot 7 is: 7, and its index is: 7 vec[7].a = 7
[I]max element of vec.a between slot 5 and slot 8 is: 8, and its index is: 8 vec[8].a = 8
[I]max element of vec.a between slot 6 and slot 9 is: 9, and its index is: 9 vec[9].a = 9
However, I now need to search and find an element of vector<myStruct> according to just one member of myStruct, instead of finding the maximum or sorting as before. This presents a problem because the function std::find does not accept such a comparison function as its third argument.
This was the description of the std::find function that I found: find - C++ Reference
Code:
template <class InputIterator, class T> InputIterator find (InputIterator first, InputIterator last, const T& val);
I could also find another function called std::find_if, but this only accepts a unary predicate like this: find_if - C++ Reference
Code:
template <class InputIterator, class UnaryPredicate> InputIterator find_if (InputIterator first, InputIterator last, UnaryPredicate pred);
And once again this is either inadequate of I don't see how to use it directly, because for the third argument I would like to insert a function that takes two arguments with a syntax like this:
Code:
int x=7;
std::vector<S>::iterator result;
result = std::find(vec.begin(), vec.end(), []( const (int x, const S & S_1) { return ( x == S_1.a ) ; } ) ;
Is there another std function that I can use to make search and find an element according to just one member of myStruct?
Or perhaps there is a clever way to pass two arguments to the unary predicate.
I am currently making pong using visual C++ with the SDL libary. I find that the ball moves too fast for the players and needs to slow down. The code for the movement is in a while loop and vairies speeds 1 - 2 (X and Y).
CODE:
//ball movement{
ballX += speedX;
ballY += speedY;
//}
ballX and ballY is the position of the ball.
speedX and speedY are the speeds. these change from 1 - 2
How to make the ball move less than one pixel or something along those lines.
I have two menu items. When item 1 is disabled, I want item 2 to be disabled as well. In the OnUpdate handler of menu item 1, I have tried to use "t_pMenu = pCmdUI->m_pMenu;", "t_pMenu = pCmdUI->m_pSubMenu;" and "t_pMenu = pCmdUI->m_pParentMenu;" but I always get NULL t_pMenu. How can I achieve this purpose?
Code:
void CDummyView::OnUpdateMenuItem1(CCmdUI* pCmdUI)
{
if(m_bShowMenuItem1) {
pCmdUI->Enable(TRUE);
[Code]....
I just want to know how fast can C++ generate data? For example, I have a downstream device that is connected to my pc via a Gigabit Ethernet, and I have to generate some pattern and send it over the Gigabit interface.
I was curious if there is a way that I can see how fast I can generate data? I was curious if I can exercise a good portion of the bandwidth ! for example, sending about 600 Mbits/sec.
How do I find out, first, whether I can do this with C/C++, and, second, how do I know how fast I am sending data?
I can not understand huge pointer, how its working.
#include<stdio.h>/ *How its working &decleration*/
int main(){
int huge *a =(int huge *)0x59990005;
int huge *b =(int huge *)0x59980015;
if(a == b)
printf("power of pointer");
else
printf("power of c");
return 0;
}
For example let say there is vector [1,2,3,4,5,6,7,8,9] and let say there is int n
if i say n=3
I want to find all possible 3 combination
[1,2,3][1,2,4].....such and such
if i say n=4
[1,2,3,4][1,2,3,5]......
I want to know how you write the code depend on the input n. Is it call dynamic programming?
So the program reads contents from a text file into a vector and then the user enters in a string that they want to search for. The program iterates through the vector to find the string and then saves that line to another vector to display later(incase there is more then 1 instance of the string found).
Here is what I have atm:
void doSearch(vector<string> &phonelist, string searcher, vector<string> &holdNumbers)
{
int i = 0;
string value;
[Code].....
I just get an R6010 error -abort() has been called.
Im currently trying to find the mode of a vector through a map but am not sure how to do so besides the attempt ive made
void mode(vector<double>v)
{
map<double, int> map;
[Code]....
i am looking for a verified code in simple c, for generating fft of an input image (.jpg). the output can be a text file including fft coefficients.can you recommend me any source except open-cv?
View 6 Replies View RelatedI'm attempting to build a column based database, and I'm new to C++ (just wanted to play around with building a column base database "for the fun of it"). I want to construct a very fast radix sort, that would allow me to quickly sort groups of columns based on integer values. My general preference is to take up more RAM to get more performance.
I'd like to build the radix sort by allowing 256 "buckets" to drop values in as I'm sorting. This allows me to sort through a group of 4 byte integers in only 4 passes. But assuming I'm trying to sort a large group of values (say 50+ million), I'm not sure what type of container to use for these. Also note I'm pretty unfamiliar with the "standard library", so below are my thoughts:
Vectors:
-Pros: Easy to use, and very fast for sequential and random access inserts / reads
-Cons: If they have to dynamically resize because a given vector wasn't large enough, this can apparently really slow performance. Unless I make another pass over the numbers before I start sorting, I wouldn't know how big to make individual the individual vectors. This means I either have to make them "too big" and waste space, or pay a performance price for either resizing, or scanning data first.
Lists:
-Pros: Seems like I wouldn't have to specify size ahead of time, so I could just easily insert values to a given list. Also, since I don't need random access reads (I'll ready the "0" list sequentially, then the "1" list, etc. they should work fine.
-Cons: I don't really know much about lists, but I'm not sure how easy it is to append a new value to the end of a list. I've read that standard library lists include both "forward" and "backward" pointers, which I don't need. Also, I find it hard to believe that there isn't some time taken up with memory allocation. If I build a list and append x million records in it, is it calling memory allocation routines x million times?
Or maybe there's another container type I should learn?
Again, my goal is to make this "fast", not "memory efficient". But having said that, the fastest way I could think of (use 256 vectors, each sized equal to the total number of members to be sorted) is just too much memory to burn - 256 times a vector big enough to hold millions of elements is too much.
I have a SSD and I am trying to use it to simulate my program I/O performance, however, IOPS calculated from my program is much much faster than IOMeter.
My SSD is PLEXTOR PX-128M3S, by IOMeter, its max 512B random read IOPS is around 94k (queue depth is 32). However my program (32 windows threads) can reach around 500k 512B IOPS, around 5 times of IOMeter!!! I did data validation but didn't find any error in data fetching. It's because my data fetching in order?
I paste my code belwo (it mainly fetch 512B from file and release it; I did use 4bytes (an int) to validate program logic and didn't find problem).
#include <stdio.h>
#include <Windows.h>
/*
** Purpose: Verify file random read IOPS in comparison with IOMeter
**/
//Global variables
long completeIOs = 0;
long completeBytes = 0;
int threadCount = 32;
unsigned long long length = 1073741824; //4G test file
[Code] ....
I’m writing an application for raw image processing but I cannot allocate the necessary block of memory, the following simple code gives me an allocation error.
double (*test)[4];
int block = 32747520;
test = new double[block][4];
off course with smaller block size (i.e. int block = 327475;) it works fine. Is there an allocation limit? How it is possible to deal with big blocks of memory?
I have been coding a while on a 2D random terrain game. How would I go about saving the maps? I have an array for blocks, lighting, background and background lighting. The lighting is done in real-time, so exclude that.
But with two 32000x3200 arrays, I still need to store 204800000 separate numbers in a file. Oh god. How can I have this? I could write down the separate numbers, but...yeah.
If it matters, this is made in freeglut.
Im trying to implement a way to use really big numbers to be able to add, substract and multiply them with the class I made. for example:
huge a = "45646464646455464654656"
huge b = "456464564646544646"
huge c = a+b;
[Code]....
Ok my assignment has me doing vector math with some canned code provided for me by the instructor This is the header file to the class I'm working with and the .cpp file as far as I've gotten it.
#pragma once
#include "Scalar.h"
class Vector2D {
public:
Vector2D();
Vector2D( const Vector2D& ) ;// copy constructor
Vector2D( Scalar element[2] ) ; // initialize with an array
[Code] ....
I'm having trouble seeing which data members I'm multiplying together and what the initial state, continuing state, and after loop action I'm supposed to be using in the for loop.
I defined the following function to find out the iterator of a certain value in the vector. I defined it as such so if the value exist in the vector then return a iterator of it, if not then return a pointer pointing to nonsense.:
vector<tIndex_t>::iterator unlabelTit(const tIndex_t index) {
for(vector<tIndex_t>::iterator it=unlabelT.begin(); it<unlabelT.end(); it++) {
if(index==*it) return it;
} return NULL;
}
But looks this one is not accepted by compiler, saying I cannot do this kind of comparison like:
unlabelTit(i)!=NULL;
so I just delete the return NULL; and then the compiler giving me warning about no return statement before }.
a pointer pointing to nonsense? how to do that?
I have this class I have been working with,
Code:
// objects to hold results, row id, and name
class result_holder {
public:
// initialize class members
result_holder() : row_id(0), row_value(0.0), row_name("") { }
[Code] ....
There are cases where I need to find an object based on the value of row_id and delete the object from the vector row_results. I could find the proper object by looping through the vector and testing against each member.
Code:
// id I am looking for
unsigned int id_to_delete = 12;
for(i=0; i<row_results.size(); i++) {
if(id_to_delete == row_results[i].row_id) {
delete row_results[i];
}
}
I have used find before to find the position in a vector with a specific value, but I don't know how to use find to locate a specific value for an object member.
Also, is delete what I need to get rid of the object or should I be using erase as in,
Code:
// id I am looking for
unsigned int id_to_delete = 12;
for(i=0; i<row_results.size(); i++) {
if(id_to_delete == row_results[i].row_id) {
row_results.erase(row_results.begin()+i);
}
}
i have a spec for fetch the files from server and predict the un-used files from the directory in this situation i am going to fetch the files from server it will return huge files, the problem is the cpu usage will increase while i am fetching large files, so i like to eliminate this scenario.
View 1 Replies View RelatedI am trying to understand what techiques can be used to sort really huge files (larger than available memory). I did some googling and came across one technique.
1. Are there any better ways to get this done?
2. Is there some tweaking that can be done to make this itself better?
Large enough so that you get a lot of records, but small enough such that it will comfortably fit into memory
3. How do you decide on this value? Consider, memory is 4 GB and currently about 2GB is consumed, and file to sort is 10GB in size. (Consumed memory could of course change dynamically during execution - consumed more/less by other apps.)
I'm trying to sort my vector, find duplicate values using unique and erase them. Program can compile successfully but the duplicates are not removed.
output:
x: 3
y: 2
x: 6
y: 4
x: 3
y: 2
vector<Point2D> p2dvector;
void readData()
[Code].....
I also have operator== in my Point2D class which I understand it is required to use unique for vector.
bool operator==(const Point2D& lhs, const Point2D& rhs)
{
return lhs.x == rhs.y;
}
Okay, so for an assignment I need to write a function called find() that returns a reference to a vector. So I have vector <int> & find(string & key); If I do this, I get the obvious warning warning: reference to local variable 'lineNum' returned [enabled by default].
If I do vector<int> & find(string & key) const; I get a huge error that starts out like
In member function 'std::vector<int>& index_table::find(std::string&) const':
indextable.cpp:74:30: error: no match for 'operator='
Am I using the const identifier incorrectly?
This program is to solve a word maze and find the number of words in the maze from a dictionary file.
The program runs, but stops by finding 1,2 and 3 letter words.
#include<iostream>
#include<vector>
#include<fstream>
#include<algorithm>
#include<string>
using namespace std;
int main() {
vector <string> dict,forward,reverse;
[Code] .....
I also tried to find words using the entire vector as a container, the synopsis code that also did not work is below
while(j<dict.size()) {
if(dict[j].size()>2) {
if (std::find(forward.begin(), forward.end(), dict[j]) != forward.end()) {
cout<<"found word "<<dict[j]<<endl;
[Code] ....
Attached File(s)
dumpling2.txt (2.54K)
Dictionary.txt (718.34K)