C/C++ :: Know That Data Written To Shared Memory Segment In Unix Is Stored Properly
Mar 8, 2012
I am trying to write a client/server application that takes input to an array of structures from the user,stores the data in a shared memory segment and then writes the same to a file when I close the application. How do I get started? And how do I ensure that the server stores the data correctly? Also, the server needs to be a concurrent server that accepts connections from multiple clients.
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Sep 28, 2013
printf is a part of code segment but found in data segment.....why is it so ?
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Mar 21, 2013
So, if I'm right, computer store their data as binary values. So if I write int x = 5; , my computer converts the value of x from decimal (5) into binary (101) and stores it in memory as a a binary number. If I print that value on the screen that value is converted(by default) back into a decimal number before being printed on the screen.
Now, my question is if there is any way to print the value of x directly into binary(as it's stored in memory) without it being converted back into a decimal value?
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May 22, 2013
I have created a shared object in Ubuntu (libMYLIB.so). I am now trying to compile a simple test program (testmylib.c) to see if the shared object is properly built. I am getting an error that the build cannot find the shared object. My build command is:
gcc -lm -l /dir/mylib -lMYLIB.so -o testmylib testmylib.c
where /dir/mylib is where my source and libMYLIB.so reside.
What am I doing wrong?
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Dec 26, 2012
My Application is C# winform
I am facing below error at the time of form close and end of Dispose() method .
The instruction at "0xXXXXXXXX" referenced memory at "0xXXXXXXXX", The memory could not be "written". Click on OK to terminate that program.
how to avoid / catch this error .
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May 31, 2013
I would like to cipher data segmet of my executable say with a simple Caesar Cipher algorithm, i.e. any text should not be readable when executable opened with a hex editor.
It should be something that converts my plain text into a ciphered form at compile time(CPP?), and when executable is being run, should be able to convert ciphered data into human readable text.
I thought meta-programming could be the approach for this. Also, implementing complex algorithms with C pre-processor (CPP) sounds vulnerable (well, depends on one's coding skills let me say)
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Apr 13, 2014
Say now I have a dll, loaded and run by a 32bit program. One of the things that I access from the program in the dll are several 1024x1024 int buffers. However I would like to put some data into those buffers from a external process. And I would like a separate thread in that external process for each buffer. Is there any way I can make that memory space accessible to the external process so I can use my own multi threaded memory transfers to pass that data over provided I ensure that the original process doesn't try to do anything with that data? And I would like to do this without resorting to the Read/WriteProcessMemory functions which are not threadsafe. In short, I want to set up direct memory access between the 2 programs without creating any intermediate shared memory buffers ie I want to set permissions for an existing memory space. Is this possible?
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Feb 9, 2013
I am not so experianced with c++ myself, but I need to evaluate if a certain idea might work.
I am working with a system for automation purposes that is running on a realtime OS in parallel to windows. Windows and the RTOS exchange data via shared memory. The application in the RTOS is compiled in C++. Now I would like to be able to influence the some data manipulation tasks in the RTOS application without changing the code of the RTOS application. So a concept like calling a dll.
My idea was to create a class with virtual methods in the RTOS application. The objects that are used should then be created on the Windows side with the same class prototype, but specific implementation of the virtual methods. The objects should then be moved to the shared memory, where they are used by the RTOS application.
Is something like this possible or am I completly on the wrong path?
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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 16, 2014
I have one requirement to store an array of structure at shared memory. Also the shared memory should have one counter to store number of elements in the array.
I tried to look at some placed but didn't find anything relevant.
So my first question, is it possible that we can store two things on same shared memory. And second if not then how to achieve the same?
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Dec 8, 2014
I am trying to initialize a 2D char array of strings into POSIX shared memory to be shared between 3 other processes. There are plenty of tutorials on how to use a pointer to share a single string or an integer between processes, but I could find no examples on how to initialize 1D or 2D arrays using mmap(). I have posted what I have so far below. It is the first program, which creates the shared memory object and initialize the array char files[20][2][100] with the value files[0][0][0] = ' '. What is the proper method to initialize and share an array in C?
(program initializes shared memory object and array)
Code:
#include<fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/shm.h>
#include <sys/stat.h>
#include <sys/mman.h>
int main (int argc, char *argv[]){
[Code] ......
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Jun 27, 2014
I have trouble reading the last element in a struct.I do get the correct value for the first two elements. In my example that is:
a = 11 and c = H
however I get:
b = 0
but I am expecting b=2
I got two files to handle this.The first one is writing data to memory -
Code:
#include <sys/shm.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
}
[code]....
why I cannot get correct value for the third element in my struct?In the second file where I'm reading from memory I allocate some space. Is this incorrect in some way? I'm running this on a Linux machine.
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Jul 11, 2014
I was trying to put mutex lock on shared memory but my code is not working. What I want is that if some process is putting something on shared memory segment, other process should not be able to access that segment. For testing , I create a server program which put data in shared memory and client program which access the data.
To test it, I put break point after:
pthread_mutex_lock(&(init_lock));
But I see that client program was able to access shared memory.
Below is code:
Server: Code: pthread_mutex_t init_lock = PTHREAD_MUTEX_INITIALIZER;
main()
{
char c;
[Code].....
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Jan 30, 2014
I'm working on a project that is supposed to create 3 processes. Process 1 should count from 1 to 100,000. Process 2 from 1 to 200,000. Process 3 from 1 to 300,000. I've written the basic code of it but my processes aren't printing out very accurate numbers.
Here's my code:
/*ass1*/
#include <stdio.h>
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/shm.h>
#include <stdlib.h>
#include <unistd.h>
/* change the key number */
#define SHMKEY ((key_t) 8450)
typedef struct
[code]....
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Aug 18, 2014
I have a question concerning shared memory (in linux-environment). In our company we currently have an application that is restarted once in a while. There are multiple instances running of this application (on different physical machines), and all access the same centralized database. Because of IO and Network bottleneck the start gets very slow, and takes about 10 Minutes. Besides some new data, most of the data stays the same, so reading from the database again is quite redundant. An idea is to write all relevant object to a shared memory segment, when the application is shut down. A second dummy process attaches to the same shared memory (just so that some process is still attached). If the application is restarted, it is attached again to its shared memory, and reads it to its own adress range again. There might occur a difference regarding the data so it might me necessary to load some new data afterwards, but that is different problem.
The current idea is to serialize all Objects (could be about 1-2 Gigabyte) with Apache Thrift, and write them into shared memory. With Thrift the data is more or less ordered, so creating the objects anew is possibly easier (not sure here).
My Question is:
- Does it even make sense to consider shared memory in this scenario. I've read a lot stuff about in the last few days, and for now I don't see big disadvantages (except if the application crashes, in this case I've to read from database again). On the other hand I don't know how to really implement this functionality (as I'm no experienced Developer)
- Should I aim for Boost::Interproces, considering even memory mappable files, or stay with the traditional shmat (and stuff..)?
- I guess 1-2 Gigabyte shared memory will be necessary. This amount is only needed in the gap between application shutdown and restart. Will the sheer amount of needed shared memory be a problem (all examples I found just used a few Bytes or Kilobytes)
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Jan 18, 2015
The file is open, the program has exclusive access to the file, no data is written at all. Even the TestLine fails to write.
Save.open("SaveFile.mystery");
if (!Save.is_open()) {
cout<< "Not open.";
getch();
[Code] .....
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Aug 23, 2014
For example when I have:
Class A{
B objectB;
};
Now when I instantiate the object of class A like:
main(){
A objectA;//option 1
A* pObjectA = new A();// option2
}
How is objectB stored in memory (stack heap etc.) for both options??
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Mar 18, 2013
i cant display the data written to this file in a switch statement (case 2) what am i doing wrong..the file data is being written into the text file but i cant display it
insert
Code:
#include <stdio.h>
#include <conio.h>
#include <stdlib.h>
FILE *fp; //creates a file pointer
typedef struct date_info
[Code].....
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Oct 11, 2014
I've found that with streamwriter(sw) the data isn't displayed with the written to document until you either leave scope or use sw.close I'd prefer to keep sw open as I will be writing to the file in and out, sometimes very frequently, but would also prefer the data to be viewed in real time. Is there an efficient way of going about this?
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May 23, 2014
I'm playing around and wrote a tiny program.
Code:
char bracketin[] = "thisgetsbracketed.txt";
char bracketout[] = "bracketed.txt";
char testwalk[10] = "12345678";
[Code]....
I'm incrementing the pointer to buffer 150 bytes beyond its reserved 50. I see testwalk, followed by bracketout, followed by bracketin printed by the overflow on buffer.
The memory locations are ordered descending from their call order. Why is this the case?
One would think that they would be written in ascending order as I call them. I can only assume that they're compiled bottom up - where could I read about this process?
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Jul 19, 2013
I have a class "Result" with a single template function Set(const std::string& arName, T& val) and a specialization of this function Set<Real>(const std::string& arName, Real& val) where Real is a typedef for double. The class is in a shared library and I use it in my main program. If I do result->Set<GLOBAL::Real>("U", 100.0); the wrong template function is called!
I check this by the output with std::cout.
Maybe it's a problem with the typedef.
If I link the object file of the Result class directly to my main program (no shared library), it works.
typedefs.hpp:
namespace GLOBAL {
typedef double Real;
} results.hpp
#include <iostream>
[Code] ....
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Jun 21, 2014
I am trying to build a employee management system using C, and I have done alot so far. Everything seems to work fine, but then I thought that I should let the user store the data of their employees permanently, therefore I created a file and then I store the user's given data in the txt file.
Here is the code:
#include<stdio.h>
#include<conio.h>
#include<string.h>
[Code].....
But there is some problem, and I don't seem to understand what is the problem in the code, it's just that whenever the user enters any id to search, and presses any key then nothing appears just a blank screen! I wanted to know that how can I check the ID from the text file and then display the details of the employee of that id!
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Mar 30, 2015
I have two std::string data items that contain binary data (so it may have the null character!). What is the proper way to concatenate them to preserve all of the data? I am guess a simple:
string string3 = string1 + string2;
Will not work, as it will terminate string3 on the first NULL character it encounters.
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Aug 13, 2014
How do I compare multiple datas?
I have climate data for 6 months and is trying to find the highest climate month among all 6 months. How do I do that?
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Apr 14, 2013
I'm working on a program which creates data and saves it into blocks (different files), then reloads and converts it all. the .ftl file saves properly, but for some unknown reason, it won't let me open it for input after.
Here's the significant code:
#include <iostream>
#include <fstream>
#include <string>
#include <sstream>
stringstream filename;
stringstream newfilename;
string Filename;
[Code] ....
setblock will typically = 3, but for testing purposes is set to 1. this really has me confused. the compiler i'm using is Dev-C++ 5.2.0.1 on xp. i have tried pausing the program after the output file is closed, confirming the file has been created in the proper directory before continuing but still fails the .is_open() check.
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Apr 19, 2012
The below code is giving me segment fault during delete [] (*iter) sometimes. Is it not the proper way to delete the vector with char *
Code:
#include <iostream>
#include <vector>
using namespace std;
int main() {
vector<char*> nameList;
for (int i=0;i<1000;++i)
[Code] ....
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