C++ :: Which Std Container To Choose
Sep 16, 2012
I have a pile of data, which i need to access frequently and fast. One entry consists of two unsigned ints, let`s call them source and destination.
One source can have several destinations, but this rarely ever happens. Several sources can have the same destination - this happens more frequently, but still scarcely.
Once the data is set up, it rarely ever changes - yet it should be possible to add or remove entries.
I now need to find all sources for a given destination, or all destinations for a given source.
The question: which stl container to choose?
I have tried a multimap, using the source as key. This works good for finding all d for a given s, but is inefficient in the other direction.
Do you think it would be more efficient to have two multimaps, sorted respectively by source and destination?
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Oct 20, 2014
#include "stdafx.h"
#include "iostream"
using namespace std;
int main (){
int x;
int i;
int e;
[Code] ....
is the logic good ? and why the program is looping
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Feb 12, 2015
I'm using waveinOpen to capture sound from my microphone. I know how to set how many channels to use, but how do you tell it what channel to use - left or right?
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Jun 18, 2013
Here is the code,
Code:
vector<int> vec;
for(int i=0;i<10;++i)
vec.push_back(i);
random_shuffle(vec.begin(), vec.end());
nth_element(vec.begin(), vec.begin()+7, vec.end());
No matter how I choose the second argument passed to nth_element, the elements in vec are always sorted as,
0,1,2,3,4,5,6,7,8,9
What is the use of second argument here?
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May 24, 2014
I am working on a program in C# that should make a user choose a specific path for the program to work.
The path they are choosing is a path for a game and from that selected path I use coding to load pictures from to the program.
Anyhow
I am able to make the user choose a path and save the selected path in a xml file.
But the user can select ANY path.
How could I do to make the user choose a specific path that I want them to choose?
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Jul 25, 2014
I've just started using the CImg library and when I try to load a picture with this code:
CImg<unsigned char> image("example.bmp");
It works perfectly. But when I try to type in the image file name using the console it gives me errors. For example, if I try this:
std::string input_file;
std::cin >> input_file;
CImg<unsigned char> image(input_file);
It doesn't work. The way I see it, I should be able type "example.bmp" into input_file and use it but it doesn't work, and gives me the error:
"error: no matching function for call to 'cimg_library::CImg<unsigned char>::CImg(std::string&)"
I have included iostream and string.h.
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Aug 1, 2013
I've read that we can write a program that displays a menu of commands for the user to choose from.We can write some functions that implement these commands, then store pointers to the functions in the array :
Code:
void ( *file_cmd[])(void) = { new_cmd , open_cmd }; // 2 cmd's for simplicity
We can get a similar effect with a switch statement but using an array of function pointers gives us more flexibility since the elements of the array can be changed as the programm is running.
I decided to write an example about this in order to understand better the context, I am facing some problems though :
Code:
#include<stdio.h>
#include<stdlib.h>
typedef void (*p_foo) (int);
void foo(int x);
void foo2(int y);
[Code] .....
The problems are :
Code:
TEST2.c:9: warning: initialization from incompatible pointer type
TEST2.c:9: warning: initialization from incompatible pointer type
TEST2.c:25: error: too few arguments to function "*(arr + (long unsigned int)((long unsigned int)i * 8ul))"
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Aug 4, 2013
I am doing my assignment that will calculate total tax amount per day and per week and finally sum those up.
One of the requirement is to filter out any number in the array that is less than 1000 to be assigned a value of zero instead of the stored value so as not to add it in the calculation. How to fulfill this requirement.
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Dec 2, 2013
Dynamic memory allocation in array in c programming. I am trying to make the user to choose the size of array they want to engage in the game.
However, i have remove the global variable which contribute the error to my code previously. Now I assigned all the arr individually but not using the global variable. However, i still not get the desired board i want. i still keep getting 9x9 array board.
And i also need limit the board size only from 4 to 9. And how do i do that.
Code:
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#include <conio.h>
#include <malloc.h>
#include <ctype.h>
#include <stdbool.h>
[Code] .....
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Apr 6, 2014
I am currently having problems creating a loop that will allow my user to choose to return to the beginning of the program or quit.
#include <iostream>
using namespace std;
int main() {
int j;
do {float a;
cout << "+----Welcome to Basic Operations----+
| Select Your Operation |
[Code] .....
I have not yet finished designing the interface for a couple of the operations, but right now i am hung up on trying to return to the beginning. I believe it is because the j was defined inside do and isn't carried out of the do statement for while.
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Mar 27, 2014
So I'm writing an RPG and I'm in need of an inventory system. Of course as an relatively old member of the forum I know best than just come here and ask so I've already researched quite a bit and I've formulated this idea.
I've kind of conceptualized it like so: I'll have some sort of STL container of a unique_ptr of my base item class. There will be derived item classes. Taking advantage of polymorphism I can then call the new Derivedclass when inserting it in the STL container.
My questions are: What STL container should be used for the inventory(fixed sized)?
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Sep 22, 2013
What is container class? what its advantage ?
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Mar 6, 2013
I am trying to come up with a way to make use of a "multilevel dynamic" container. I am parsing a file to grab some pieces of data. Lets say the first field of data I find I push into an array. At the same time lets I wish to create 2 cascaded sublevels. So an element in Modules is a pointer to the Types vector associated with that module and each element in Types is a pointer to a vector of Data. This concept should be similar to memory paging.
/*
Modules Types Data
____ _____ ______
|____|------> |_____| ---------->|______|
|____| |_____| |______|
|____| |_____| |______|
|____|
|____|
|____| _____ ______
|____|------> |_____|----------->|______|
|____| |_____| |______|
*/
Obviously this becomes very hair quickly so it is obvious that I need to dynamically create and destroy vectors (if I do it this way). Should I just create pointers using the new operator?
Here is some of my code if it is even worthwhile to read:
class Parser {
//storage arrays
vector <string> modules;
vector <string> terminal_type;
vector <string> tag_type;
vector <string> data;
[Code] ....
parse this stuff and nicely organize it.
If you take the first one, "max_logvar" is a module so everything between < and > is associated with that module.
symb is unimportant for now.
then "proterm" is a "module type" so then module now needs a module type container but I may have more than one of those.
so then I break it down by "Input" and "Output" where each of those can have the integer values (just in an array where each position will be set) that are in the fields to the right.
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Nov 21, 2013
I have a container in c++11 and i must delete first object and i don't know how...
for (const prob& p : *static_cast<vector<prob>*>(list.listData)){
// i must delete the first object
}
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Apr 25, 2014
How do we design a container of objects all of which belong to some subclass which directly/indirectly inherits from a given parent class? Moreover, I would like to have functions that enable me to pick only objects of a certain class type from the container.
For example if the parent class is A and I have a hierarchy of classes that derive from it, we must have a container that can contain any class that exists in this hierarchy. Also, get_B() must be able to let me examine only those objects in this container that inherit (directly/indirectly) from class B (class B exists in the hierarchy rooted at A).
Preferably, we would like to avoid downcasting. Or even explicit typechecking of any sort.
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Mar 30, 2014
To my understanding, a Container should have an Allocator member data, which is used internally.
Question: what happens, for example, when we swap() two containers that use different allocators?
Must the allocators be swapped as well?
Must all elements of the container be reallocated when the allocator is changed?
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Jun 24, 2013
I need to create an array container with the same structure as double myA [100][100];. But I cannot declare it as array<double, 100, 100> myA; however I do need this container for its format. How can I make it work.
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Feb 9, 2013
I know that it's a class that contains data from another class I just do not know how to make them both work together.
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Jun 14, 2013
i built a programming language called jade that right now can only print. i want to add variables to it however. I am going to use a modified bajarne stroustrop calculator to handle expressions (ie will now include string manipulations and such), but I want to build a var class into the program to make it easier for the program. i want variables to act like python variabes, and arrays to act like python associative arrays. Ive scoured different containers, but they only work if the variable isnt an array in my language, because it will only have one type. the only thing i can come up with is a union and 4 overloaded = operators (for bool, int, double, and string) is there a better way to do this?
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Oct 31, 2013
so i have a container called Source that is of type std::map<std::string, std::vector<std::string>> but when I try to print it with this function:
void Lexer::PrintSource()
{
for(auto Iterator = this->Source.begin(); Iterator != this->Source.end(); Iterator++)
for(auto SubIterator = Iterator->begin(); SubIterator != Iterator->end(); SubIterator++)
cout<< *SubIterator << endl;
}
i get these errors:
Lexer.cpp: In member function 'void Lexer::PrintSource()':
Lexer.cpp:29:42: error: 'struct std::pair<const std::basic_string<char>, std::vector<std::basic_string<char> > >' has no member named 'begin'
for(auto SubIterator = Iterator->begin(); SubIterator != Iterator->end(); SubIterator++)
^
Lexer.cpp:29:76: error: 'struct std::pair<const std::basic_string<char>, std::vector<std::basic_string<char> > >' has no member named 'end'
for(auto SubIterator = Iterator->begin(); SubIterator != Iterator->end(); SubIterator++)
^
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Nov 23, 2013
I have a deposit of containers and i must delete the cats container. How i can do that?
#include <iostream>
#include <string>
#include <vector>
using namespace std;
struct Cat {
string name;
int age;
[Code] .....
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May 13, 2014
I want to find all instances of a substring mysub in array container myarr and replace each occurrence of mysub with empty string " ". To do that, I'd like to use for loop with search algorithm.
Code below:
p=array iterator
for ( p=search(myarr.cbegin(),myarr.end(), mysub.begin(),mysub.end();
p!=myarr.end();
p=search(p,myarr.end(),mysub.begin(),mysub.end() ); {
[Code] ......
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Jun 30, 2014
I need a "meaningful" way of accessing a table, the column is representing Err magnitude, and the row is representing Rate magnitude. For each error magnitude and rate magnitude, i define an action magnitude, which is the contains of the table. For example,
Code:
int matrix[10][10];
int Action1 = matrix[0][0];
int Action2 = matrix[0][1];
However, i need a better way of getting matrix[0][0], row and col itself is meaningless. I want to access the table like
"Action magnitude" = matrix["Rate magnitude 1"]["Err magnitude 2"]; using a string instead of int id.
How to easily do this in c++ container?
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Jan 16, 2012
I have a class called CTestObject and it has one variable int id. I want to add instances of this to an std container and be able to:
1. quickly determine if the value of "int id" exists in the container and update the object
or
2. add a new object to the container
Which std container is the best for this application? What method should I use to search the container for the object id?
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Feb 21, 2012
How do you find, when you first introduced with say some of the STL container, function or algorithms, what are its requirements? I mean,
1. what operators object should have for specific container?
2. what function args and type it should return for a algo?
3. when extending some container like with custom allocator, char_traits...and what not, what methods should be overridden? What work should they do?
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Jun 15, 2014
When using an iterator with a std container (list / vector etc) sometimes it's possible to modify the container (e.g. delete an item) yet still carry on using the iterator - whereas in other cases, modifying the container immediately invalidates any open iterators on it. Is there an easy way to know which containers fall into which category? (or does it vary from one compiler to another?)
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