Migrating old MQL4 to new MQL4

**newdigital** · 02-12-2014, 05:02 AM

Migrating old MQL4 to new MQL4

This guide is for people that want to migrate existing MQL4 scripts to work with the new terminal build as quickly as possible without taking advantage of the new object oriented contructs available.
It has been collated from various posts on the mql4 forum.
Disclaimer: I've not tested all of this myself! First read as much as you can about the language changes (ignoring any Object Oriented related stuff).
Then check you code for all of the following contructs and review/fix...
In some cases the fixes below are not as good as restructuring your code to properly use the new features!
Once running, if your script is still a work in progress you may want to add the

#property strict directive and recompile again. This will mean you need to make more changes , to get your code to compile cleanly but it will result in cleaner code and may find some bugs.

New Reserved Keywords

MQL4 has some new reserved keywords such as 'char','long','short' and 'new'. If you have variables with the same name you'll need to change them. datetime is 64bit

The datetime type is a 64bit integer, so you will get loss of precision errors converting to int(which is 32bit). Avoid converting it to any other type but datetime

ArrayCopyRates()

This has changed to making a static copy of the rates array (as opposed to pointing to a virtual area that is updated with each tick). Change code to use the new CopyRates() GetLastError()

GetLastError does not reset the previous error anymore. Call ResetError as required. Or replace with:
int GetLastErrorOld() { int err = GetLastError(); ResetError(); return err; } The Data Folder Location

Change all reference to file data paths. eg TerminalPath() becomes either TerminalInfoString(TERMINAL_DATA_PATH); or TerminalInfoString(TERMINAL_COMMONDATA_PATH) Unicode(UTF16) Strings

Strings are now unicode in MQL4. When passing strings to DLL functions either:
1. Use the UTF16(2byte wide) version of the function Eg. Use ShellExecuteW instead of ShellExecuteA
2.Convert the string to ASCII and use the existing function Arrays pass by value

You cannot pass arrays by value. There are two simple fixes:
1. If the function does not modify the local array, then simply pass it by reference (adding '&' ), and if applicable add a comment "do not modify local array"
2. If the function modified the local copy, then change it so it doesnt - eg make a local copy inside the function and use that. StringSubstr - end of string flag

The end-of-string flag is changed from 0 to -1 in line with MQL5. Also if thre start character is less than 0 then new MQL4 may corrupt strings. Use the following when migrating existing code:
string StringSubstrOld(string x,int a,int b=-1) { if (a < 0) a= 0; // Stop odd behaviour if (b<=0) b = -1; // new MQL4 EOL flag return StringSubstr(x,a,b); } It might be possible to #define this. Short Circuiting

Boolean expresions now short circuit. So if an expression contains a function call, that function would always get called on old MQL4, but might not get called in new MQL4. If the function changed something in the program (ie had a side effect), and that change is required to happen, then place the function call ahead of the boolean expression. Eg. replace and ensure functions with required side effects are called ahead of expression evaluation.
if (Ask > price && GetNextPrice(price2)) then ... with
bool tmp = GetNextPrice(price2); if (Ask > price && tmp) ) then ... Precedence

MQL4 Precedence is changed. In Old MQL4 boolean OR(||) had higher precedence than boolean AND(&&). Inew new MQL4 the precedence is the same. Search for expressions where || folow && and add brackets around immediate || arguments. History Files

History files and offline charts are changed. I must admit I haven't looked into these changes because I have not used these features. Sorry! Bug build 604: ArrayResize on non-dynamic arrays fails silently

Compiler should issue a warning when trying to resize a non-dynamic array. see Forum post Bug build 604: FileReadArray bug with strings

Strings are corrupted when read. Use FileReadString(handle) in a loop until fixed. see Forum post Bug build 604: Array Resize returns size of first dimension

ArrayResize returns size of first dimension not whole array. Contrary to documentation... Cant find thread where this was reported.. old version:
double ratesArrayCopy[][6]; int size = ArrayResize(ratesArrayCopy, 10); //I got size= 60 new version:
double ratesArrayCopy[][6]; int size = ArrayResize(ratesArrayCopy, 10); //I got size= 10 ?

**newdigital** · 02-12-2014, 05:03 AM

The table of differences between compilers:

Old MQL4 compiler	New MQL4 compiler	New MQL4 with #property strict
init(), start() and deinit() entry points may have any parameters and any return type	init(), start() and deinit() have been remained intact for compatibility, while new OnInit(), OnStart(), OnCalculate(), OnTick(), OnTimer(), OnChartEvent(), OnTester() and OnDeinit() should strictly correspond to their signatures	Ditto
Virtually any variable names (except for the reserved words) are possible, including special characters and points	Variable names cannot have special characters and points. The list of the reserved words has been expanded. Thus, such widespread words as short, long, const, etc. cannot be used as names	Ditto
Variable scope is from declaration (even in the nested block) to the function end	Ditto	Variable scope is from declaration to the end of the block, in which the variable is declared
Implicit initialization of all the variables (both global and local ones) by zero	Ditto	Only global variables are initialized. In local variables, only strings are initialized implicitly
Local arrays are not released when exiting the function	Local arrays are released when exiting the function	Local arrays are released when exiting {} block
"Array out of range" does not cause a critical error	Ditto, except for the arrays of structures and classes, for which this error is critical one	"Array out of range" is a critical error causing the program to stop
No structures and classes	Structures and classes are present. Additional data types are implemented	Ditto
Strings are single-byte. datetime is a 32-bit integer Predefined Volume variable is of double type	Strings are unicode ones. datetime is a 64-bit integer Predefined Volume variable is of ulong type	Ditto
ArrayCopyRates() performs virtual copying to double[][6] array	ArrayCopyRates() performs virtual copying to MqlRates[] array. Copying to double[][6] array has remained intact for the sake of compatibility, however, that copying is real, not virtual.	Ditto
The functions may not return values even if they have a type. To do this, return(0) is automatically inserted by the compiler in the function end	Ditto	Functions of any type should return a value
The number of simultaneously opened files is 32	The number of simultaneously opened files is 64	Ditto
The files are always opened in FILE_SHARE_READ, FILE_SHARE_WRITE mode **	FILE_SHARE_READ and/or FILE_SHARE_WRITE should be specified explicitly	Ditto

**newdigital** · 02-12-2014, 05:59 AM

Get Ready to Meet New MetaTrader 4 with Updated MQL4 Language

The beta test of the new MetaTrader 4 version is currently underway. The update's main features include changes in MQL4 programming language. It has been substantially revised, and its functionality has been brought closer to that of MQL5.

Of course, we have made every effort to ensure compatibility with older MQL4 applications. However, some issues may still occasionally occur. If you have encountered an error while compiling a new code, please inform us in the appropriate thread of the official MQL4 forum.
We also urge you to pay special attention to the following points:

1) In the new build, the file structure for storing the source codes has changed. Previously, all MQL4 programs were stored in Program Files\<terminal_installation_folder>\ root directory. Now, they should be stored in Users\<data_folder>\MQL4\. Thus, if a program has an absolute pathname for some file, you may run into an error message in the compiler. To avoid this, specify a relative pathname in the source code and re-compile it. The data folder can be accessed via File -> Open Data Folder.

2) All old EX4 files will work correctly in the new terminal assuming that they are not changed. In order to maintain compatibility, the runtime environment copy of the previous MQL4 version has been implemented providing operability of all older codes.

Find out more about all changes in the new MetaTrader 4 build here. We strongly recommend that you have a close look at the provided material.

**newdigital** · 02-12-2014, 06:03 AM

MetaTrader 4 Build 600 with Updated MQL4 Language and Market of Applications Released :

All custom executable EX4 files created by old MQL4 compiler will be automatically moved to the new Navigator directory and will work in the new terminal the same way as before.

**newdigital** · 07-21-2014, 11:46 AM

I want to remind one thread - Requests and Raw Ideas.

I mean - if someone is having the difficulties to improve/fix some indicator/EA to new builds of MT4 - use this thread for request.

**mql5** · 06-12-2016, 09:59 AM

Upgrade to MetaTrader 4 Build 600 and Higher

Migrating old MQL4 to new MQL4-509to610all_f_1.png

On February 3, 2014 we released the new MetaTrader 4 build 600 with the completely revised MQL4 language and access to the Market of applications.
In addition to the updated MQL4 language for programming trading strategies, the new version of the MetaTrader 4 terminal provides a revised structore of user data storage. In earlier versions all programs, templates, profiles etc. were stored directly in the terminal installation folder. Now all necessary data required for a particular user are stored in a separate directory called data folder. However, some traders who have never worked with the latest versions of Windows may have question about the operation of the new terminal.

**matfx** · 11-24-2016, 10:22 AM

An article about migrating indicators/EA from MQL4 to MQL5

https://www.mql5.com/en/articles/81

**Taylor Woods** · 08-23-2019, 10:25 AM

Great FX brokers will enable you to store funds and pull back your income bother free. Brokers really have no reason to make it difficult for you to pull back your benefits in light of the fact that the main reason they hold your funds is to encourage trading. Your broker just holds your money to make trading simpler so there is no reason for you to experience serious difficulties getting the benefits you have earned. Your broker should ensure that the withdrawal procedure is expedient and smooth.

**jagadish123** · 08-23-2019, 02:49 PM

ND, why we are seeing this msg iin many threads?

Originally Posted by Taylor Woods

Great FX brokers will enable you to store funds and pull back your income bother free. Brokers really have no reason to make it difficult for you to pull back your benefits in light of the fact that the main reason they hold your funds is to encourage trading. Your broker just holds your money to make trading simpler so there is no reason for you to experience serious difficulties getting the benefits you have earned. Your broker should ensure that the withdrawal procedure is expedient and smooth.