C++ :: Malloc Virtual Memory - Handling Page Movements?
Jul 23, 2012
When does malloc() return null ? I want to allocate a big virtual memory which can not possibly fit on RAM, so most of it will be stored on disk. I am going to access the data sequentially so at any one time the data I am working on will fit in RAM. So I am hoping the OS will move the required pages in and out of disk. I can achieve this behavior manually by allocating the required blocks on RAM but this is rather tedious. Say I have an array a[100][10000000000]. At any one time I am working only on a[i-1][], a[i][], a[i+1][] which can fit in RAM but not the whole array. So how do I allocate the array so that I can work on it using for loops for(i=0;i<100;i++) without handling the page movements myself?
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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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Dec 1, 2014
I am writing a very basic database in C++ and I am accessing the data from a web browser. I am using the opensource Mongoose web server code....
I have an issue...
The way the DB works is this: on starting, the DB loads a json file of all of the data into it. I have a class called DatabaseLoader that does this - it is the class that gets rewritten depending on the data structure of the json.
This is passed to vectors (vector<Node*> and vector<Edge*>) as references from Graph object.
Once the DatabaseLoader has finished it can be destroyed and any memory allocated objects it created (except the ones in those two vectors).
From then on, the Graph object is in charge of all of the elements in the database that are stored in the two vectors. When the user browses to htpp://127.0.0.1:8000 they see the json representing each object in the vectors.
All good so far....
However, when I repeatedly hit refresh in my browser (and call me insane...) at quite a fast speed I get this error:
Code:
main(29855,0x7fff76763310) malloc: *** error for object 0x7f98b2829408: incorrect checksum for freed object - object was probably modified after being freed.
*** set a breakpoint in malloc_error_break to debug
[1] 29855 abort ./main testing.json
It seems to me this would be if I tried to "delete" and object twice, or if one of my objects was overwriting memory somewhere. However I am not recreating anything, I am just looping over the vectors and printing out the content. When I refresh slowly, I dont see this happen - i did it quite a lot of times, but when I do it fast I think it is happening.
So is there any possibility of me hitting the c++ web server to quickly and it is trying to process the data twice, causing some sort of memory error - i.e do I need to implement threading or something??
I can paste code, but there is quite a lot now....
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May 16, 2014
does memory reserved by malloc() get freed when the function it is called in finishes?
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Nov 5, 2014
There is a part in the lesson that explains how malloc is used to allocate free memory to a pointer and gives us 2 examples:
Code:
float *ptr = malloc( sizeof(*ptr) ); and Code: float *ptr;
ptr = malloc( sizeof(*ptr) );
From my logic in the first case we allocate the memory to *ptr and in the second to ptr.
It's a bit confusing, am I missing something?
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Sep 7, 2013
How can I view the number of bytes that have been allocated by using the malloc function?I tried:
mem = (float*)malloc(num*sizeof(float));
printf("The amount of memory allocated using malloc is %d.", mem);
Note: The variable "num" in my program is equal to 7.But every time I run the program, this value changes.
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Jun 13, 2014
Consider this program:
Code:
// sb_string class v1.04
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
typedef struct sb_string {
[Code] ....
And here is the output I got:
Code:
[harshvardhan@hari-rudra] ~/Desktop% gcc49 -o test test.c
[harshvardhan@hari-rudra] ~/Desktop% ./test
-before Value of len = 1
(in_function)-before Value of len = 1
(in_function)-after Value of len = 1
-after Value of len = 1 I was trying to make a little easier to work with string. Once the memory is allocated by malloc via sb_init() function, the sb_massacre function wasn't working to deallocate the memory. I had used multiple versions of gcc and clang but the result is same.
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May 11, 2012
I have a question about the KLU library for LU factorization of sparse matrices. The KLU library accepts a pointer to a memory allocator function, by default it is malloc(). Then it uses this pointer to allocate the memory required.
I want to extend the library and I now have object of classes. I want to use the operator new instead of malloc to allocate the memory. In the same time I want the new operator to call the constructors of the objects. Is there a way to do it?
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Mar 10, 2014
What is wrong with my function why does it spit out huge numbers? And how do i use malloc or calloc to create an array in dynamic memory, and return a pointer to this array
Code:
#include <stdio.h>#include <stdlib.h>
int fibonacci(int n)
{
int i;
long int fib[40];
fib[0]=0;
fib[1]=1;
for(i=2;i<n;i++){
fib[i] = fib[i-1] + fib[i-2];
[Code]....
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Apr 17, 2014
My application calls malloc in multiple subroutines, finally releasing all using free. This is done using my zalloc library (see my other post: [URL] .....
Somehow, when the applications tries to detect the available ammount of memory at the end of the test (allocating, freeing, testing), the freemem function gives me about 4-6MB less memory than at the start of the test? (out of 21MB available on the device at the start).
All memory is allocated and freed using the malloc/free routines within the library, with the exception of the SDL functions, which are registered externally on allocation and release.
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May 27, 2014
In interprocess communication(IPC) when processe have to share data among each other,why cant they all connect to one single file and share data with basic file handling functions such as read and write?
Why do we need
shared memory(shmget shmat(),shmdt()..etc)
and
mapped memory(mmap(),munmap()..etc)
concepts?
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Jan 26, 2013
I have a program which call only one time malloc at the start of the program. When running, I see with 'process-explorer.exe' that memory is growing in little steps. Is this normal? why?
Using Windows 7
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Jan 8, 2014
I'm trying to keep track of the size of blocks of memory that a pointer points to. No matter what I do, this code below always outputs the integer 8.
If I change 1000 to 5, I still get 8. If I change it to 0, I get 8... If I change it to -1, I get 8. If I change int *a to double *a, I get 8. If I take away the & symbol, I get 8. If I use *& instead, I get 8.
Why? I want it to output 1000. If I change that to 500, I want it to output 500.
int *a;
a = malloc(1000 * sizeof(int));
int j = sizeof(&a);
printf("%d", j);
I want to build my skills where I can allocate, inspect and change memory sizes.
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May 19, 2014
I am working on an OOP assignment (text handler) which part of its description is:
Some lines of text as a story which the delimiter between each story is %%%%%
Each text loaded should only occupy the space needed for the text to fit.
It's required to use dynamic variables of type char*. To be more detailed, the text-handler must contain a vector of such char-pointers (i.e. c-strings), and the parameter in the constructor indicates how many pointers (c-strings) to be contained in the vector. Each loaded text will be represented by a number, so that the first text in the file gets number 0 and the next one gets number 1 ... etc. When you want to access a text, you request the text with a certain number, and then get a pointer in return that may be used to output the text on the screen.
My problem is first to allocate a dynamic memory like char** without defining the number of array elements (Each text loaded should only occupy the space needed for the text to fit. )and then store each story from text file (comprise of a few lines of text) into that dynamically located memory(char **)to be able to do some operation on it later.
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Jul 29, 2014
I have found that when I dump a C++ object from memory to a file - it seems that there is a misplacement of the last Virtual-Function-Table pointer - in that appears at the beginning. The result is that the gdump information based on this object dump (using green hills) is incorrect. I copied the contents of the gdump information below. The executable is compiled in linux.
Basically MEIO::CameraStatus contains an item that relates to its parent class (line 188). Then it has 18 items that are all Diagnostics::EventsCounter items. Now for each Diagnostics::EventsCounter item there is a Virtual-Function-Table Info Pointer as its last item. All is fine and good except that the last item of MEIO::CameraStatus which is _selfReset is missing its last item of 4 bytes (which is the Virtual-Function-Table Info Pointer ). On the other hand - right before the first Diagnostics::EventsCounter item ("_vidErrors") - there is an extra 4 bytes which happens to be the Virtual-Function-Table Info Pointer. As I said the gdump information file does not see this.
Why the object memory "moves" the last Virtual-Function-Table Info Pointer to the beginning (right before _vidErrors) and is there a way to "fix" this?
///////////////////////////////////////////////////////////////////////////
"MEIO::CameraStatus" val:0x000002f0 ind208,-1) Struct-Begin Info
188: "" offset 0, Parent-Class Private Info C++ Struct ref = 114
189: "_vidErrors" offset 160, Member Info C++ Struct ref = 128
190: "_vdiErrors" offset 480, Member Info C++ Struct ref = 128
[Code] .....
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Jan 24, 2015
I m making calendar in server control page by taking composite control.I am also adding textbox in each cell of calendar. Now i want to access the value of each textbox of selected month and respected date in default.aspx page on button click event. Here the button is not a custom control but defined in default.aspx page..
Can't access textbox text and date or controls of server page in website(default.aspx) page.
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Dec 27, 2012
class Parent{
public:
virtual int width();
virtual int height();
int area(){return width()*height();};
[Code] ....
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Nov 7, 2014
DisplayImages.aspx.cs file
using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Net;
using System.IO;
using mshtml;
using HtmlAgilityPack;
[Code]...
Now I'm getting the value of id i.e "DisplayImages.aspx?id=3" from DailyDarshan.aspx and want to display the images of each respective link according id.. when I click on "DisplayImages.aspx?id=4" link so it has to show the if(id == 4) images...but The problem is int id its not taking value itself.on DisplayImages.aspx.cs page I must have to define the id. for e.g. I wrote int id =3; on DisplayImages.aspx.cs file so it shows the images of id = 3 on each and every link.. Tell me what should I do to take value from another page or else how int id takes value by itself...
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Nov 22, 2014
I am a bit unsure about what this piece of code aligning a struct to a page is trying to achieve.
Code:
#define PAGESIZE 1 << 12
typedef struct __attribute__((aligned(PAGESIZE))) x86_pagetable {
x86_pageentry_t entry[PAGETABLE_NENTRIES];
} x86_pagetable; It is an piece of code from an educational operating system WeenyOS.
What is the essence of aligning a struct to a page?
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Sep 13, 2014
i want to write a c++ program that could pass a web page request, using a php script in a dns server. And also passed by the quested page to the software. What i really want to do is a software that can redirect a page request.
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Apr 10, 2014
What is the best way to save a c# web page to database, either sql or oledb both fine. What I am looking to do is save all the data that has been entered into a database then upload this data to a grid view or form view.
The problem is there is a a lot of data on the page. Such as drop down lists, check boxes panels text boxes. I am able to display the text boxes in the database when i enter information into them. this is not working for the other objects. Also there is fixed data in the panels which doesn't require user input but I still want this info saved as it is vital.
In short I want to save the data from a page ive created called DOCare.aspx into a database. then take the data and display it in Forms.aspx a different page, where it will list all the completed forms for the user to modify if needed.
How to do this or links to websites that have information on this?? Dont know if i am wording it wrong but just cant find a way to do this. Everyone ive seen is working with small amounts of data and only text boxes.
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Nov 12, 2014
I decided to code my own GUI menu. getting to another page from a button click. I have added the event handler I think (click="Button_click") then in the event handler I have added this:
private void Button_Click(object sender, System.EventArgs e);
}
Response.Redirect("Login.xaml");
}
After researching it says either to use
Response.Redirect("Login.xaml");
OR
Server.Transfer("Login.xaml");
Neither of these work, underlining "Response" and "Server" as an error saying "A namespace cannot directly contain members such as fields or methods."
NOTE: MY MAIN GUI PAGE IS CALLED "mainpage.xaml" THE CODE ABOVE IS STORED IN THE "mainpage.xaml.cs" THIS MIGHT BE RIGHT OR WRONG BUT I'M NOT SURE SO I AM LEAVING SOME EXTRA INFO!
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Aug 31, 2014
I have a secnario where I have few tab controls one ineide the other, where my real tab pages containing the data are 4 level deep. This entire structure is dynamically built from a data base.
Now I have a tick event, on whice I want to update the data in the currently selected tabpage.
How can I find it, recall that I have many tab controls, each has a tabpage with another tab control an so forth...
Two ideas I had in mind, I though I caould generate a list of all my data TabPages and itterate it, but I failed to find an indicator of the selected tab.
Another idea was to track the currently selected tabpage via an event, but I feared that I might miss somehow the track and my update the wrong tab page.
Last idea was really unelegant - Look at the main control, get the selected tab page, find the tab control on that page via searching its controls, than find this control selected page, and do the same until I reach the 4th level.
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Sep 20, 2012
I have a test web page and a windows form which call a printer and sends a print job to a printer that is on the network. I have been able to successfully do this from the windows form, however, I can figure out how to do it from an aspx page to the server's default printer. Sample codes are below.
Windows Form:
public partial class Form1 : Form {
private const string TEMPLATE_DIRECTORY = @"C:Program FilesBrother bPAC3 SDKTemplates"; // Template file path
private const string TEMPLATE_SIMPLE = "NamePlate1.LBX"; // Template file name
private const string TEMPLATE_FRAME = "NamePlate2.LBX"; // Template file name
public Form1() {
InitializeComponent();
[Code] ....
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Nov 2, 2013
I wrote a program to detect if a graph is tree or not. Initially it was using static memory. Later I changed it to use memory dynamically using malloc().My problem is that, my program it works great for case when graph is not tree but fails if it is.
Code:
#include <stdio.h>
#include <stdbool.h>
#include <stdlib.h>
int main()
}
[code]....
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May 11, 2014
I am trying to make a simple c++ program that will read some text in the html page. Here is the source of the html i want to read.
<html>
<body>
This is a test message.
</body>
</html>
My expected result in c++ in an string array like this:
This
is
a
test
message
I tried to look around and I came across a function called InternetReadFile but I can't find any example similar to what I want.
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