forked from rosh/MQL5Book
90 lines
3.8 KiB
MQL5
90 lines
3.8 KiB
MQL5
//+------------------------------------------------------------------+
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//| FileOpenClose.mq5 |
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//| Copyright 2021, MetaQuotes Ltd. |
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//| https://www.mql5.com |
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//+------------------------------------------------------------------+
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#include "..\..\Include\MqlError.mqh"
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#include "..\..\Include\PRTF.mqh"
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// NB: we will open some files twice in the same script
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// just for demonstration purpose;
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// normally you need only one handle for a file per program instance
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//+------------------------------------------------------------------+
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//| Script program start function |
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//+------------------------------------------------------------------+
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void OnStart()
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{
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int ha[4] = {}; // reserve some space to hold file handles for all tests
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// the next file should exist, because it's left from FileSaveLoad.mq5
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const string rawdata = "MQL5Book/rawdata";
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// this should succeed because it's 1-st time we open the file
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// and it's existing and not locked by other software;
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// Note: obtained handles are just integer numbers
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ha[0] = PRTF(FileOpen(rawdata, FILE_BIN | FILE_READ)); // 1 / ok
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if(ha[0] == INVALID_HANDLE)
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{
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PrintFormat("File %s is inaccessible,"
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" but should exist after FileSaveLoad test run.", rawdata);
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return;
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}
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// this will fail, because neither of the open calls allow sharing
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ha[1] = PRTF(FileOpen(rawdata, FILE_BIN | FILE_READ)); // -1 / CANNOT_OPEN_FILE(5004)
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// let's close initial handle and reopen it with sharing for read
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FileClose(ha[0]);
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ha[0] = PRTF(FileOpen(rawdata, FILE_BIN | FILE_READ | FILE_SHARE_READ)); // 1 / ok
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// now the second call will succeed
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ha[1] = PRTF(FileOpen(rawdata, FILE_BIN | FILE_READ | FILE_SHARE_READ)); // 2 / ok
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// now try to open it for modification (reading + writing)
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// writing was not allowed for sharing in previous handles, so the new request fails
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ha[2] = PRTF(FileOpen(rawdata, FILE_BIN | FILE_READ | FILE_WRITE | FILE_SHARE_READ)); // -1 / CANNOT_OPEN_FILE(5004)
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const string newdata = "MQL5Book/newdata";
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// NB: if you run the script second time the file "newdata"
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// might be existed, so we need to simulate clean environment
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// and delete the file
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if(FileDelete(newdata)) // cleanup for next execution of the test
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{
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PrintFormat("Note: file %s was left from previous run,"
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" deleted for proper test case.", newdata);
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}
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// let's try to open non-existing file for reading
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ha[3] = PRTF(FileOpen(newdata, FILE_BIN | FILE_READ)); // -1 / CANNOT_OPEN_FILE(5004)
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// and now create such new file
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ha[3] = PRTF(FileOpen(newdata, FILE_BIN | FILE_READ | FILE_WRITE)); // 3 / ok
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// try to write some data into the same file using FileSave,
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// this fails because sharing was not specified above
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long x[1] = {0x123456789ABCDEF0};
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PRTF(FileSave(newdata, x)); // false
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// let's close the file and reopen it with all sharing options
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FileClose(ha[3]);
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ha[3] = PRTF(FileOpen(newdata, FILE_BIN | FILE_READ | FILE_WRITE | FILE_SHARE_READ | FILE_SHARE_WRITE)); // 3 / ok
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// this time we can write into the same file using FileSave,
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// which simulates "external access" to the file
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// in the sense that it's performed bypassing our handle in ha[3]
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PRTF(FileSave(newdata, x)); // true
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// you may look into MQL5/Files/MQL5Book/ folder to find 8-bytes length "newdata" file
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// graceful close of all files
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for(int i = 0; i < ArraySize(ha); ++i)
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{
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if(ha[i] != INVALID_HANDLE)
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{
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FileClose(ha[i]);
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}
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}
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}
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//+------------------------------------------------------------------+
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