Modifying an object in Boost shared

Modifying an object in Boost shared_memory

I'm learning shared memory of boost to apply it to my OpenCV project.
These are two snippets for testing.

class.h

#ifndef _class_H_

#define _class_H_

class Myclass{

public:

    Myclass() : number(0){}

    int number;

};

#endif

write.cpp

#include <boost/interprocess/managed_shared_memory.hpp>

#include <cstdlib>

#include <iostream>

#include "include/class.h"



int main(int argc, char *argv){

   using namespace boost::interprocess;

   struct shm_remove{

      shm_remove() { shared_memory_object::remove("MySharedMemory"); }

      ~shm_remove(){ shared_memory_object::remove("MySharedMemory"); }

   } remover;

   managed_shared_memory segment(create_only, "MySharedMemory", 65536);

   Myclass *instance = segment.construct<Myclass>("instance1")();          

   instance = new Myclass();

   std::system("read.exe");

   std::cout << instance->number << std::endl;

   return 0;

}

read.cpp

#include <boost/interprocess/managed_shared_memory.hpp>

#include <cstdlib>

#include <iostream>

#include "include/class.h"



int main(int argc, char *argv){

    using namespace boost::interprocess;

    managed_shared_memory segment(open_only, "MySharedMemory");

    std::pair<Myclass*, managed_shared_memory::size_type> res;

    res = segment.find<Myclass> ("instance1");

    res.first->number = 3;

    return 0;

}

Surely the output must be 3, but it is 0, which means that the class is not modified.
How can I modify an object in shared memory?

edited Nov 24 '18 at 17:15

user10605163

2,838624

asked Nov 24 '18 at 15:58

Wang chen

You are not using the instance created in the shared memory, instead you are creating a local one and outputting its value (instance = new Myclass();).

– user10605163
Nov 24 '18 at 16:04

There's not a single line of OpenCV code here. Please, don't use irrelevant tags.

– Dan Mašek
Nov 24 '18 at 16:52

@DanMašek My mistake. I forgot to remove it

– Wang chen
Nov 24 '18 at 17:15

@eukaryota I made a silly mistake. Thanks!

– Wang chen
Nov 24 '18 at 17:20

add a comment |

I'm learning shared memory of boost to apply it to my OpenCV project.
These are two snippets for testing.

class.h

#ifndef _class_H_

#define _class_H_

class Myclass{

public:

    Myclass() : number(0){}

    int number;

};

#endif

write.cpp

#include <boost/interprocess/managed_shared_memory.hpp>

#include <cstdlib>

#include <iostream>

#include "include/class.h"



int main(int argc, char *argv){

   using namespace boost::interprocess;

   struct shm_remove{

      shm_remove() { shared_memory_object::remove("MySharedMemory"); }

      ~shm_remove(){ shared_memory_object::remove("MySharedMemory"); }

   } remover;

   managed_shared_memory segment(create_only, "MySharedMemory", 65536);

   Myclass *instance = segment.construct<Myclass>("instance1")();          

   instance = new Myclass();

   std::system("read.exe");

   std::cout << instance->number << std::endl;

   return 0;

}

read.cpp

#include <boost/interprocess/managed_shared_memory.hpp>

#include <cstdlib>

#include <iostream>

#include "include/class.h"



int main(int argc, char *argv){

    using namespace boost::interprocess;

    managed_shared_memory segment(open_only, "MySharedMemory");

    std::pair<Myclass*, managed_shared_memory::size_type> res;

    res = segment.find<Myclass> ("instance1");

    res.first->number = 3;

    return 0;

}

Surely the output must be 3, but it is 0, which means that the class is not modified.
How can I modify an object in shared memory?

edited Nov 24 '18 at 17:15

user10605163

2,838624

asked Nov 24 '18 at 15:58

Wang chen

You are not using the instance created in the shared memory, instead you are creating a local one and outputting its value (instance = new Myclass();).

– user10605163
Nov 24 '18 at 16:04

There's not a single line of OpenCV code here. Please, don't use irrelevant tags.

– Dan Mašek
Nov 24 '18 at 16:52

@DanMašek My mistake. I forgot to remove it

– Wang chen
Nov 24 '18 at 17:15

@eukaryota I made a silly mistake. Thanks!

– Wang chen
Nov 24 '18 at 17:20

add a comment |

I'm learning shared memory of boost to apply it to my OpenCV project.
These are two snippets for testing.

class.h

#ifndef _class_H_

#define _class_H_

class Myclass{

public:

    Myclass() : number(0){}

    int number;

};

#endif

write.cpp

#include <boost/interprocess/managed_shared_memory.hpp>

#include <cstdlib>

#include <iostream>

#include "include/class.h"



int main(int argc, char *argv){

   using namespace boost::interprocess;

   struct shm_remove{

      shm_remove() { shared_memory_object::remove("MySharedMemory"); }

      ~shm_remove(){ shared_memory_object::remove("MySharedMemory"); }

   } remover;

   managed_shared_memory segment(create_only, "MySharedMemory", 65536);

   Myclass *instance = segment.construct<Myclass>("instance1")();          

   instance = new Myclass();

   std::system("read.exe");

   std::cout << instance->number << std::endl;

   return 0;

}

read.cpp

#include <boost/interprocess/managed_shared_memory.hpp>

#include <cstdlib>

#include <iostream>

#include "include/class.h"



int main(int argc, char *argv){

    using namespace boost::interprocess;

    managed_shared_memory segment(open_only, "MySharedMemory");

    std::pair<Myclass*, managed_shared_memory::size_type> res;

    res = segment.find<Myclass> ("instance1");

    res.first->number = 3;

    return 0;

}

Surely the output must be 3, but it is 0, which means that the class is not modified.
How can I modify an object in shared memory?

edited Nov 24 '18 at 17:15

user10605163

2,838624

asked Nov 24 '18 at 15:58

Wang chen

I'm learning shared memory of boost to apply it to my OpenCV project.
These are two snippets for testing.

class.h

#ifndef _class_H_

#define _class_H_

class Myclass{

public:

    Myclass() : number(0){}

    int number;

};

#endif

write.cpp

#include <boost/interprocess/managed_shared_memory.hpp>

#include <cstdlib>

#include <iostream>

#include "include/class.h"



int main(int argc, char *argv){

   using namespace boost::interprocess;

   struct shm_remove{

      shm_remove() { shared_memory_object::remove("MySharedMemory"); }

      ~shm_remove(){ shared_memory_object::remove("MySharedMemory"); }

   } remover;

   managed_shared_memory segment(create_only, "MySharedMemory", 65536);

   Myclass *instance = segment.construct<Myclass>("instance1")();          

   instance = new Myclass();

   std::system("read.exe");

   std::cout << instance->number << std::endl;

   return 0;

}

read.cpp

#include <boost/interprocess/managed_shared_memory.hpp>

#include <cstdlib>

#include <iostream>

#include "include/class.h"



int main(int argc, char *argv){

    using namespace boost::interprocess;

    managed_shared_memory segment(open_only, "MySharedMemory");

    std::pair<Myclass*, managed_shared_memory::size_type> res;

    res = segment.find<Myclass> ("instance1");

    res.first->number = 3;

    return 0;

}

Surely the output must be 3, but it is 0, which means that the class is not modified.
How can I modify an object in shared memory?

c++ boost-interprocess

edited Nov 24 '18 at 17:15

user10605163

2,838624

asked Nov 24 '18 at 15:58

Wang chen

edited Nov 24 '18 at 17:15

user10605163

2,838624

asked Nov 24 '18 at 15:58

Wang chen

edited Nov 24 '18 at 17:15

user10605163

2,838624

edited Nov 24 '18 at 17:15

user10605163

2,838624

edited Nov 24 '18 at 17:15

user10605163

2,838624

asked Nov 24 '18 at 15:58

Wang chen

asked Nov 24 '18 at 15:58

Wang chen

asked Nov 24 '18 at 15:58

Wang chen

You are not using the instance created in the shared memory, instead you are creating a local one and outputting its value (instance = new Myclass();).

– user10605163
Nov 24 '18 at 16:04

There's not a single line of OpenCV code here. Please, don't use irrelevant tags.

– Dan Mašek
Nov 24 '18 at 16:52

@DanMašek My mistake. I forgot to remove it

– Wang chen
Nov 24 '18 at 17:15

@eukaryota I made a silly mistake. Thanks!

– Wang chen
Nov 24 '18 at 17:20

add a comment |

You are not using the instance created in the shared memory, instead you are creating a local one and outputting its value (instance = new Myclass();).

– user10605163
Nov 24 '18 at 16:04

There's not a single line of OpenCV code here. Please, don't use irrelevant tags.

– Dan Mašek
Nov 24 '18 at 16:52

@DanMašek My mistake. I forgot to remove it

– Wang chen
Nov 24 '18 at 17:15

@eukaryota I made a silly mistake. Thanks!

– Wang chen
Nov 24 '18 at 17:20

You are not using the instance created in the shared memory, instead you are creating a local one and outputting its value (instance = new Myclass();).

– user10605163
Nov 24 '18 at 16:04

There's not a single line of OpenCV code here. Please, don't use irrelevant tags.

– Dan Mašek
Nov 24 '18 at 16:52

@DanMašek My mistake. I forgot to remove it

– Wang chen
Nov 24 '18 at 17:15

@eukaryota I made a silly mistake. Thanks!

– Wang chen
Nov 24 '18 at 17:20

add a comment |

0

active

oldest

votes

Your Answer

StackExchange.ifUsing("editor", function () {
StackExchange.using("externalEditor", function () {
StackExchange.using("snippets", function () {
StackExchange.snippets.init();
});
});
}, "code-snippets");

StackExchange.ready(function() {
var channelOptions = {
tags: "".split(" "),
id: "1"
};
initTagRenderer("".split(" "), "".split(" "), channelOptions);

StackExchange.using("externalEditor", function() {
// Have to fire editor after snippets, if snippets enabled
if (StackExchange.settings.snippets.snippetsEnabled) {
StackExchange.using("snippets", function() {
createEditor();
});
}
else {
createEditor();
}
});

function createEditor() {
StackExchange.prepareEditor({
heartbeatType: 'answer',
autoActivateHeartbeat: false,
convertImagesToLinks: true,
noModals: true,
showLowRepImageUploadWarning: true,
reputationToPostImages: 10,
bindNavPrevention: true,
postfix: "",
imageUploader: {
brandingHtml: "Powered by u003ca class="icon-imgur-white" href="https://imgur.com/"u003eu003c/au003e",
contentPolicyHtml: "User contributions licensed under u003ca href="https://creativecommons.org/licenses/by-sa/3.0/"u003ecc by-sa 3.0 with attribution requiredu003c/au003e u003ca href="https://stackoverflow.com/legal/content-policy"u003e(content policy)u003c/au003e",
allowUrls: true
},
onDemand: true,
discardSelector: ".discard-answer"
,immediatelyShowMarkdownHelp:true
});

}
});

draft saved

draft discarded

Sign up or log in

StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});

Post as a guest

Name

Required, but never shown

StackExchange.ready(
function () {
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fstackoverflow.com%2fquestions%2f53459889%2fmodifying-an-object-in-boost-shared-memory%23new-answer', 'question_page');
}
);

Post as a guest

Name

Required, but never shown

0

active

oldest

votes

0

active

oldest

votes

draft saved

draft discarded

Thanks for contributing an answer to Stack Overflow!

Please be sure to answer the question. Provide details and share your research!

But avoid …

Asking for help, clarification, or responding to other answers.

Making statements based on opinion; back them up with references or personal experience.

To learn more, see our tips on writing great answers.

draft saved

draft discarded

Sign up or log in

StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});

Post as a guest

Name

Required, but never shown

Post as a guest

Name

Required, but never shown

Sign up or log in

StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});

Post as a guest

Name

Required, but never shown

Sign up or log in

StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});

Post as a guest

Name

Required, but never shown

Sign up or log in

StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});

Post as a guest

Name

Required, but never shown

Name

Required, but never shown

Name

Required, but never shown

This page is only for reference, If you need detailed information, please check here

搜尋此網誌

Btukfyl