{"id":507,"date":"2013-12-09T21:14:54","date_gmt":"2013-12-10T01:14:54","guid":{"rendered":"http:\/\/templesystems.com\/?page_id=507"},"modified":"2013-12-09T21:14:54","modified_gmt":"2013-12-10T01:14:54","slug":"memory-mapped-file","status":"publish","type":"page","link":"https:\/\/templesystems.com\/?page_id=507","title":{"rendered":"Memory Mapped File"},"content":{"rendered":"

#include<\/span> <string><\/span><\/span><\/p>\n

\n

using<\/span><\/span> namespace<\/span>
\nstd<\/span>;<\/span><\/p>\n

\/**************************************************************************************************<\/span><\/p>\n

\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 <\/span>CMemMapFile<\/span><\/span><\/p>\n

\u00a0 \u00a0 \u00a0 \u00a0<\/span>A\u00a0<\/span>Class to store a structure in a memory mapped file.<\/span><\/p>\n

\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 <\/span>The\u00a0purpose for using a memory mapped file is to cross process boundaries.<\/span><\/p>\n

\u00a0<\/span>\u00a0 \u00a0 \u00a0\u00a0<\/span>This\u00a0<\/span>simple class only has a constructor, destructor, and <\/span>accessor<\/span>.<\/span><\/p>\n

\u00a0<\/span>\u00a0 \u00a0 \u00a0 <\/span>Use\u00a0<\/span>is as follows:<\/span><\/p>\n

struct<\/span><\/span><\/span> MyDataStruct<\/span>\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 <\/span>\/\/ this could also be “class MyDataStruct<\/span>“<\/span><\/p>\n

{<\/span><\/p>\n

\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 <\/span>int<\/span><\/span> x;<\/span><\/p>\n

\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 <\/span>int<\/span><\/span> y;<\/span><\/p>\n

}<\/span><\/p>\n

SomeFunctionThatNeedsMemoryMappedData<\/span><\/span><\/span>()<\/span><\/span><\/p>\n

{<\/span><\/p>\n

\/\/ create the data file<\/span><\/p>\n

\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 <\/span>CMemMapFile<\/span><MyDataStruct<\/span>> myData<\/span><\/span>(<\/span>_T(“MyFunctionsMemoryMappedDataFile<\/span>“));<\/span><\/p>\n

\/\/ use the data file<\/span><\/p>\n

\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 <\/span>if(<\/span>myData<\/span>)<\/span><\/p>\n

\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 <\/span>{<\/span><\/p>\n

\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 <\/span>myData<\/span><\/span>->x = 5;\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0<\/span>\/\/ assign, which stores to mem<\/span> mapped file<\/span><\/p>\n

\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 <\/span>myData<\/span><\/span>->y = 5;<\/span><\/p>\n

\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 <\/span>cout<\/span><\/span> << myData<\/span>->x;\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 <\/span>\/\/ access data (from mem<\/span> mapped file)<\/span><\/p>\n

\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 <\/span>cout<\/span><\/span> << myData<\/span>->y;<\/span><\/p>\n

\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 <\/span>}<\/span><\/p>\n

\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 <\/span>else<\/span><\/span><\/p>\n

\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 <\/span>cout<\/span><\/span> << “Construction\u00a0of myData<\/span> failed!!”<\/span><\/p>\n

\/\/ destructor will get called when <\/span>myData<\/span> goes out of scope, and get rid of file<\/span><\/p>\n

}<\/span><\/p>\n

**************************************************************************************************\/<\/span><\/p>\n

\u00a0<\/span><\/p>\n

template<\/span><\/span> <class\u00a0<\/span>T><\/span><\/p>\n

class<\/span><\/span> CMemMapFile<\/span><\/span><\/p>\n

{<\/span><\/p>\n

public<\/span><\/span>:<\/span><\/p>\n

\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 <\/span>CMemMapFile<\/span><\/span>(<\/span>wstring<\/span> Name);\u00a0 \u00a0 \u00a0 \u00a0<\/span>\/\/ must construct with a name<\/span><\/span><\/p>\n

\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 <\/span>~CMemMapFile<\/span><\/span>(<\/span>);\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0<\/span>\/\/ destructor<\/span><\/span><\/p>\n

\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 <\/span>T*\u00a0<\/span>operator<\/span>–>(<\/span>) { return<\/span> m_pData<\/span>; }\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 <\/span>\/\/ access data with pointer operator e.g. myData<\/span>->x = 5;<\/span><\/span><\/p>\n

\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 <\/span>operator<\/span><\/span> bool<\/span><\/span>() { return\u00a0<\/span>m_hFile<\/span> && m_pData<\/span>;\u00a0}\u00a0 <\/span>\/\/ test for\u00a0validity e.g<\/span> if(myData<\/span>)…<\/span><\/span><\/p>\n

private<\/span><\/span>:<\/span><\/p>\n

\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 <\/span>HANDLE\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 <\/span>m_hFile<\/span>;<\/span><\/p>\n

\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 <\/span>T*\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 <\/span>m_pData<\/span>;<\/span><\/p>\n

};<\/span><\/p>\n

\u00a0<\/span><\/p>\n

template<\/span><\/span> <class\u00a0<\/span>T><\/span><\/p>\n

CMemMapFile<\/span><\/span><T>::CMemMapFile<\/span><\/span>(wstring<\/span> Name)<\/span><\/p>\n

{<\/span><\/p>\n

\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 <\/span>m_hFile<\/span> = NULL;<\/span><\/p>\n

\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 <\/span>m_pData<\/span> = NULL;<\/span><\/p>\n

\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 <\/span>if<\/span>(<\/span>Name.length<\/span>()\u00a0== 0)<\/span>\u00a0<\/span>return<\/span><\/span>;<\/span><\/p>\n

\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 <\/span>m_hFile<\/span> = CreateFileMapping<\/span>(INVALID_HANDLE_VALUE, NULL, PAGE_READWRITE, 0, sizeof<\/span><\/span><\/span>(<\/span>T), Name.c_str<\/span>());<\/span><\/p>\n

\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 <\/span>if<\/span><\/span> (m_hFile<\/span>)<\/span><\/p>\n

\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 <\/span>{<\/span><\/p>\n

\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 <\/span>m_pData<\/span> = (T*) MapViewOfFile<\/span><\/span>(<\/span>m_hFile<\/span>, FILE_MAP_READ |\u00a0FILE_MAP_WRITE, 0, 0, 0);<\/span><\/p>\n

\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 <\/span>if<\/span><\/span> (!m_pData<\/span>)<\/span><\/p>\n

\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 <\/span>CloseHandle<\/span><\/span>(<\/span>m_hFile<\/span>);<\/span><\/p>\n

\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 <\/span>}<\/span><\/p>\n

}<\/span><\/p>\n

\u00a0<\/span><\/p>\n

template<\/span><\/span> <class\u00a0<\/span>T><\/span><\/p>\n

CMemMapFile<\/span><\/span><T>::~<\/span>CMemMapFile<\/span>()<\/span><\/p>\n

{<\/span><\/p>\n

\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 <\/span>if<\/span>(<\/span>m_pData<\/span>)<\/span><\/p>\n

\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 <\/span>UnmapViewOfFile<\/span><\/span>(<\/span>m_pData<\/span>);<\/span><\/p>\n

\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 <\/span>if<\/span>(<\/span>m_hFile<\/span>)<\/span><\/p>\n

\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 <\/span>CloseHandle<\/span><\/span>(<\/span>m_hFile<\/span>);<\/span><\/p>\n

}<\/span><\/p>\n

\u00a0<\/span><\/p>\n

\n<\/div>\n

 <\/p>\n

 <\/p>\n","protected":false},"excerpt":{"rendered":"

#include <string> using namespace std; \/************************************************************************************************** \u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 CMemMapFile \u00a0 \u00a0 \u00a0 \u00a0A\u00a0Class to store a structure in a memory mapped file. \u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 The\u00a0purpose for using a memory mapped file is to cross process boundaries. \u00a0\u00a0 \u00a0 \u00a0\u00a0This\u00a0simple class only has … Continue reading →<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"parent":303,"menu_order":0,"comment_status":"open","ping_status":"open","template":"","meta":{"footnotes":""},"class_list":["post-507","page","type-page","status-publish","hentry"],"_links":{"self":[{"href":"https:\/\/templesystems.com\/index.php?rest_route=\/wp\/v2\/pages\/507","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/templesystems.com\/index.php?rest_route=\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/templesystems.com\/index.php?rest_route=\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/templesystems.com\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/templesystems.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=507"}],"version-history":[{"count":4,"href":"https:\/\/templesystems.com\/index.php?rest_route=\/wp\/v2\/pages\/507\/revisions"}],"predecessor-version":[{"id":511,"href":"https:\/\/templesystems.com\/index.php?rest_route=\/wp\/v2\/pages\/507\/revisions\/511"}],"up":[{"embeddable":true,"href":"https:\/\/templesystems.com\/index.php?rest_route=\/wp\/v2\/pages\/303"}],"wp:attachment":[{"href":"https:\/\/templesystems.com\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=507"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}