C++ :: How To Reserve Memory For Maps
Nov 26, 2014
I have a situation where map elements will be inserted all throughout a continuous loop. I know that there's no reserve function for maps like there are for vectors, but I know exactly the maximum amount of elements there will be in the map, I just don't know the value of each individual map.
Would it be possible if I just inserted the maximum amount of elements in the beginning of the program, and change the value of each/any individual element later on? For example:
std::map<int, std::string> map;
//There will be a maximum of 200 elements in this map
for (int i = 0; i < 200; i++) {
map[i];
}
//Change the value of individual elements as I wish
Is it more efficient than initializing on declaration if initializing will be done often?
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Oct 12, 2013
In my code I have a template class.
In the contructor, I create a new array arrray.
A pointer to this array is saved as an attribute.
The purpose of this attribute is that I should be able to call the array from within another function be typing *p or *(p+1) etc.
The only thing I forgot is that the array doesn't exist anymore when the constructor is done, right?
This means the space is no longer reserved for this array and the space is used for other things.
Is there a way to keep the array space reserved (even when the array does not exist anymore at the end of the function)?
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Mar 7, 2014
We can construct vector in following ways
vector<int>v1; //create an empty vector
vector<int>v2(arr,arr+4); ///to create vector from an array
vector<int<v3(v2); //throuh copy constructor
But I have come across some program in a forum,they have create vector like this
vector<int>v(10,5)
I am clueless ,is this allowed?,what syntax allows this?
if a vector is create like this
vector<int>v(3);
v.push_back(1);
v.push_back(2);
v.push_back(3)
v.resize(2);
Now I am curious to know what are the changes those will happen in vector v because of resizing it?
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Sep 15, 2014
I am writing a program that minicks the library reserve system at my university and the problem is that when i run the code and reserve a room i am to keep track of the amount of times the room has been visited. To do this i set up a array roomcount and I count up by one every time i assign a room, The bug lies with when you reserve a room, then run option three, it will show that the previous visits is at 1, which is good. but then if i leave the room(option 2) and then run option 3 again to view the status of the rooms, the previous visits is set back to 0, which is not good. Ive been staring at this for hours and asked numerous people by we can't seem to figure out why the roomcount variable resets.
#include <stdio.h>
#include <math.h>
int main (void) {
int choice;
int roomchoice;
int i = 0;
[Code] .....
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Sep 19, 2014
Currently im creating a simple phone directory. I am having a problem when searching the vector. It only lets me search for the exact key in the directory when I need to to search for strings that are close to the name. For example when I search "car" it will state that its not in the directory when it should pull up Carr, Derek and Carr David.
#include <string>
#include <map>
#include <vector>
#include <ostream>
#include <iostream>
int main() {
std::map<std::string, std::vector <std::string> > directory;
[code]....
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May 5, 2013
I've a problem with the map construct. I wrote this class in which there are maps:
class Features {
private:
map<const string,GenericFeatureContainer*> featuremap;
map<const string,GenericFeatureContainer*>::iterator it;
int size;
public:
}
And I have the following constructor:
Features::Features() {
map<NULL,NULL> featuremap;
it=NULL;
size=0;
}
Is that correct? otherwise what is the correct syntax?
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Dec 7, 2014
GameMaster.h
#includes ...
class GameMaster
{
[Code].....
I get the segmentation fault whenever it tries to insert the first player.. however whenever i do this :
void MakeSquad(char type, string name, int coordX, int coordY, char dir, int squad)
{
GameSpace::MapSquadType MapOfSquads;
MapOfSquads.insert(make_pair(name , Squad(squad)); // Squad( int ) just converts the int squad number to the Enum.
}
I do not get any errors or segmentation faults..
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Dec 29, 2014
i have made this first level in this ascii game, and i realized that if i want to continue, i must rewrite the switch statement and write thousands of lines of code. how can i load a map from a txt file?
#include <iostream>
#include <windows.h>
using namespace std;
[Code].....
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Feb 9, 2014
I have code working, but that is largely because a vector that I am using as part of a structure that is the first of two elements of a MAP (with the second being an integer that is assigned later) is serving in its original, purely vector form, to fill out a set of selections on a DOS screen (option 1, 2, 3, etc.).
I do use the MAP, because it is a simple means of referencing the integer value using a word that is part of the structure, and is probably appropriate, saving me a search through the vector of words and calling up the value at the same location in the vector of words in a vector of corresponding numerical values. I DO feel that what I'm doing to produce the selection list is something of a "cheat" because I do not know how to access the same data within the structure component of the MAP by simply using a similar numerical reference (e.g. "MAP[1].structure.word", or would that be "MAP.structure.word[1]" ????) to print out the words in the structure in the map as choices on the screen.
I don't want to change or expand the contents of the map, just access and print each one in a simple loop with a number from the loop counter to the left of each word.
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Mar 19, 2013
I had a quick question regarding a program I am trying to complete. I have the basics worked out, and everything seems to be done, but I am running into two issues.
1= The program keeps telling me "Run-Time Check Failure #3 - The variable 'order' is being used without being initialized."
and
2= When I reach my output screen I receive "Unhandled exception at 0x7751c41f in CISC 192 Project 3.exe: Microsoft C++ exception: std:Out_of_range at memory location 0x002eefb8.."
While the first one isn't necessarily a deal breaker the second one definitely is.
Code:
// Bookstore Project 3.cpp : Defines the entry point for the console application.
// Declarations
#include "stdafx.h"
#include <iostream>
#include <iomanip>
#include <cstdlib>
#include <string>
#include <istream>
[Code] ....
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May 11, 2013
I'm trying out the gmp library by building a simple pi calculation program (original, I know!). On a million digits of Pi I've debugged the program and seem to have about a megabyte too much of memory at the end of the program (I start with around 250k before any allocation begins and end at around 1200).
int main(int argc, char *argv[]) {
//set a//
int digitsofpi =1000000;
mpf_set_default_prec(log2(10) *digitsofpi );
mpf_t a;
mpf_init (a);
mpf_set_ui (a,1);
[code].....
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Mar 8, 2013
I am looking for a way to run a process form memory, without having any executable. The application will be kept inside a resource and will be extracted during run time. It should be then started as a new process. I couldn't find a solution that works also on x64
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Nov 6, 2014
We have a proprietary third-party library that we make calls into via an API. Through a series of API calls, this library manipulates specific sets of data. Prior to making these calls, there are some API calls that are necessary in order to initialize the library in preparation for a specific set of data. One of the calls tells the library to allocate some memory and then perform whatever initialization is required. This particular API call returns a pointer to char (char*) that is later used as an argument for a few other API calls. My question is... Is there a way, or maybe some kind of trick, to tell exactly how much memory was allocated? It doesn't matter whether or not the solution (if there is one) is C++ related, or some series of OS commands. FYI: We're running on Redhat Linux 6.2 and using GNU C++ 4.4.6.
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Jan 31, 2015
So, it seems I have a bug in my code:
Code:
char *mem = malloc(9), *bottom = malloc(3), *in = "abc";
int position = 2, i;
mem = "onetwo";
printf("OLD mem = %s
", mem);
[Code]....
What I'm trying to do is insert "abc" in the 3rd position of "onetwo". Results would be "oneabctwo", but all I get is crashing.
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Mar 27, 2014
Is there any way to read RAM memory directly. For say i want to access memory location 0x0100 to 0x120. How to do that. how to declare the variable, is it unsigned int. what is the type of read values it hex or ascii. how t cast it.
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Jul 14, 2013
I have declared a global variable as pointer. The program performs certain number of iterations. After every iteration, the size of memory required for the pointer changes and this pointer variable is to be accessed by different functions. Now, here is my doubt:If I allocate the memory for this global variable in a function, will the contents of the memory be lost once I exit that function. In my opinion, it should not be the case as the dynamic memory allocation takes place in "heap" and should not be affected by the call of functions.
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Oct 17, 2014
Code:
int *p, ar[100];
p = (int *)malloc(sizeof ar);
.. *p is a pointer variable, but what means another * here --> (int *)?
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Sep 18, 2013
I have created a database for music cds:
Code:
#include<stdio.h>
#include<stdlib.h>
#define array
typedef struct cd_database
[Code]....
When I am using malloc instead of arrays the code is not working properly after exit. I have tried alot but can't came up with a way
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Jun 1, 2014
Code:
# include <stdio.h>
# include <math.h>
# include <stdlib.h>
# include <malloc.h>
}
[code]...
I am compiling it on a 64 BIT ubuntu machine having 64GB ram using gcc 4.6 compiler. I am getting the following output Error allocating memory. But (914*866*2724) is approximately 8 GB, Whats wrong with the code?
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Feb 24, 2013
I need to use realloc to extend the memory when it goes out of bounds but I am not getting a correct output.
this is how i am trying to realloc
Code:
if(strlen(theString) - strlen(searchFor) + strlen(replace) >= size -1) {
size += 80;
// theString = strcpy(theString,theString);
[Code].....
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Feb 15, 2013
I am new to C++ language and I am still learning.I'm doing basic stuff to better understand dynamic memory. I was wondering why I keep getting memory issues.*/
#define SIZE 15
class word {
char* str;
public:
[code]....
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Oct 25, 2013
I'm currently learning templates -- & my logic is in a knot with what I am trying to do which is the following:
-Create a function name load
-Accepts a filename (the filename is a text file of integers)
-Open the file
-Create an array(dynamically allocating an array) filling it with the elements read in from the file & returns the array(so that the return type of the array is a pointer to the element type of the array).
//Header file:
#ifndef BUBBLE_SORT_H
#define BUBBLE_SORT_H
#include <iostream>
template <typename T>
void load(std::string filename, T *&arr, int *size);
[code].....
how to allocate memory when it comes to using templates..
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Jul 12, 2013
In the code below. I believe I am returning the memory location of the value I am looking for. How can get the value?
main.cpp
int choice = 0;
PlayerMenu *newPM = new PlayerMenu;
File *file = new File;
// Menu for loading, creating or exiting the game
choice = newPM->menuChoices();
PlayerMenu.cpp
[Code] ....
I am not sure how to deference the value so I can get at the value instead of the memory location.
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Mar 27, 2013
Is it possible to store data to CPU memory, if so how much memory can I store and how? Say I wanted to store an array, about 6MB in size?
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Sep 2, 2014
declare
int *p[3];
that gives an array with 3 pointers, but how 3 pointers can have a link in the memory?
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Dec 15, 2013
Let us consider the following two classes:
class case1
{
public:
int n;
float x;
[code]....
Now, let's suppose that I instantiate an array of 100 elements of each class:
case1 c1[100];
case2<20> c2[100];
My question is this: will c2 occupy roughly half of the memory than c1?will the value c1.n be allocated 100 times, while the value c1.n wil be allocated only once?
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