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?
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.
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?
View 1 Replies View RelatedI 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?
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?
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] ......
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.
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].....
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]....
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)
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.
View 1 Replies View RelatedWhen 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?
View 2 Replies View Relatedi'm writing a lexer, and i want to use boost::regex for it. im sure im using it right (just in case though)
while(!this->Source.empty())
{
if(regex_search(Start, End, Match, regex(""[^"]*""), Flags))
[code].....
someone told me to download the latest source and build that so i did, by unzipping it, cding to the source, running ./bootstrap.sh, ./b2, and finally ./b2 install. when i compile i get no errors but when i run it i get ./jade: error while loading shared libraries: libboost_regex.so.1.55.0: cannot open shared object file: No such file or directory
I have this code for a computer project... (store management) but the character strings are not copied on text file..
#include<iostream.h>
#include<conio.h>
#include<fstream.h>
class Store {
public:
char *item_name[5];
store()
[Code] .....
Now when i run the program, it gives a error :::
ERROR
address 0x0
How can i write these strings to the text file?
I have a folder "pics" in g: drive. There I want to create some text.txt file. Thus, the final path is "g:pics ext.txt".
How can I do that?
I've written a program to read inputs in a text file. The file named Input.txt contain integers 2 3 and 4. My program is as follows:
#include<iostream>
#include<cstdlib>
#include<fstream>
using namespace std;
int main (){
int x,y,z;
[Code] ....
the program is outputing x=2293616 , y=0 and z=0 instead of x=2, y=3 and z=4.
I need to insert my thesaurus words .txt to my c program applying BST. But I am not sure how.
Here are my file: awwwwwwww.txtthes.c
I am accepting the word from user and arranging it in ascending order like in dictionary in a file . I am doing this by comparing the user entered word from existing word in the file . All the word which is smaller then user entered word is copied to another file "temp.txt" , then the user word is printed and then the remaining word ( which are larger) from "abc.txt" to "temp.txt" . But program close as soon as i enter the second word
Code:
#include<stdio.h>
#include<string.h>
main() {
FILE *fp,*ft ;
fp = fopen("abc.txt","r+");
ft = fopen("temp.txt","r+");
[Code]....
Both file are already created before /
I got this issue to tackle which consists of using an FIR LPF filter to filter a wav file using C programming.
Till now I managed to tackle the filter part following this link: Implementation of FIR Filtering in C (Part 1) | Shawn's DSP Tutorials (I have my own filter co-efficients which have been produced using FDAtool on MATLAB and some other minor changes have been applied to match my requirements)
Now, the link shown does not compensate for files having a header. I have three wav files which need to be filtered. Thus I need to first extract the data from the header .. this was done using RIFFpad. Now that I have the data
Info from RIFFpad:
fmt -
Offset=20
ID=fmt
[Code].....
I've got this hint to start with: Each audio datasample inside the wav_files can be made up of a number of bytes and these bytes arestored in the little-endian order. Inside your program you have to change this to a big-endian order.
I'm given a project in college to use trees(AVL tree, to be specific) and file handling(not very conversant with it). But I'm not able to relate the two.
I only know that files can be used to store data. But in what way can trees and file handling be connected? I know how to implement trees but how to store it as such in files?
I have two files like original.txt and replace.txt which has equal nbr of lines in both of them.
I need to loop through these two files line by line and replace the line in original.txt to the line in replace.txt
eg :
output.txt :
1|raj|65.4|Y|
1|ramesh|65.4|Y|
replace.txt :
1|raj|65.4|Y|
Cannot be processed|1|ramesh|65.4|Y|
What I need here is when reading of output.txt reaches second line of file "1|ramesh|65.4|Y|", it has to be replaced with the second line in replace.txt "Cannot be processed|1|ramesh|65.4|Y|".
1|ramesh|65.4|Y| --> Cannot be processed|1|ramesh|65.4|Y|
After the end of loop the contents of two files should be like :
original.txt :
1|raj|65.4|Y|
Cannot be processed|1|ramesh|65.4|Y|
replace.txt :
1|raj|65.4|Y|
Cannot be processed|1|ramesh|65.4|Y|
The files can have variable number of lines but both will have same number of lines each.
i want to create/open any file present in any location in my computer. How do I assign a path in C++ syntax?
View 1 Replies View RelatedI am having a 1file (given file) and in that i have some binary information and i niw i want to convert those binary information into decimal form and save it into new file (output fle). I was written a code but that was not working properly.
Code :
main() {
int i,j,n,ch;
int a[100][100];
FILE *p,*q;
char file1[20],file2[20];
printf("enter the given file name");
[Code] ....
Every time I write in file using ofstream it works fine except for one thing that when the file is re-opened after writing something and we try to add more data then previously added data is removed how to get rid of this.
<code>
struct abc {
char name[100];
int a;
};
int main() {
ofstream file;
file.open("text.dat", ios:ut | ios::binary);
[Code] ....
Code:
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <conio.h>
#include <windows.h>
}
[code]....
I dont know how to modify the previous record that i have done in the Add Student function. i searched from different sites and got this code for modifying a record in a text file. But, i cant figure it out why its not working.
I am writing to write a program and performs the following tasks
- Reading a file (txt file contains some temperature values)
- Display the temperature values (contents of the file)
- Calculating the average of the temperature values in the file.
- finds the maximum and minim value of temperature in the file.
The program is user interactive and waits for the user input and process according to his input (choice)
I have managed to complete the program and covered all the expect except the error handling for file opening and reading, although I have managed to do it for the part one part (i.e for the choice == 1)
I can repeat it for the other choices (i.e for 2, 3 ) but I do not want to repeat the code and do it in a different function or do it once for all. While making an attempt I can not handle the rest of the program and all the program turns into a mess.
#include <iostream>
#include <fstream>
#include <iomanip>
int menu();
int myChoice(char);
char inputValidating();
[Code] .....
Need Error handling for file opening and Reading that is used once, So far I have managed to do it for choice 1
Text file can be found in the attachment