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return two values from function possible?

  • #1
  • First Post: Jul 13, 2007 5:57pm Jul 13, 2007 5:57pm
Hello, is it possible to return two values from a function in mql4 programming?
  • #2
  • Jul 13, 2007 6:00pm Jul 13, 2007 6:00pm
Quoting Heino
Hello, is it possible to return two values from a function in mql4 programming?
i'm not aware of that. in c# or c++ there is an "out" keyword we use to return multiple values.

in mq4 i am yet to see this. keep looking. check the mql site
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  • #3
  • Jul 14, 2007 5:45am Jul 14, 2007 5:45am
Hi, I now that in C and C++ it ist possible with pointer but in mql4 I dont have finde a way.

I have think before that I can put all values into a array and than return the array from the function but in mql4 I dont find a way to do this.
  • #4
  • Jul 14, 2007 10:19am Jul 14, 2007 10:19am
  •  iya
  • | Joined Oct 2006 | Status: always protect yourself | 129 Posts
Simply use "pass by reference" just as in C++, works for arrays, too:

Inserted Code
void PassByReferenceTest(int &out1, int &out2, int &outArray[])
{
    out1        = 1;
    out2        = 2;
    outArray[0] = 3;
    outArray[1] = 4;    
}
  • #5
  • Jul 15, 2007 7:13am Jul 15, 2007 7:13am
Hello, thank you for example, but how I can get now the values after I call the function, I have tried 3 examples but it dont work:

PHP Code
start(){
  
  PassByReferenceTest(1, 2, 3);
  Print(outArray[0],"  ",outArray[1]);
  // error variable outArray not defined

  PassByReferenceTest(1, 2, 3);
  Print(PassByReferenceTest(1, 2, 3),"  ",PassByReferenceTest(1, 2, 3));
  // error incompatibel types  

  PassByReferenceTest(&1, &2, &3);
  Print(outArray[0],"  ",outArray[1]);
  // error variable outArray not defined


}

//-------

void PassByReferenceTest(int &out1, int &out2, int &outArray[])
{
    out1        = 1;
    out2        = 2;
    outArray[0] = 3;
    outArray[1] = 4;    
}
However I think this dont work in mql4 just in C and C++ or ?
  • #6
  • Jul 15, 2007 7:29am Jul 15, 2007 7:29am
PHP Code
start()
{
    int xxx[2];
    int yyy;
    int zzz;
    PassByReferenceTest( yyy, zzz, xxx );
    ...
}
I.e., the arguments to the call must be variables of corresponding types, and the array elements must have been created before the call.
  • #7
  • Jul 16, 2007 5:54am Jul 16, 2007 5:54am
Hi, I have tried again,

PHP Code
start(){
 
    int out1;
    int out2;
    int outArray[3];
    PassByReferenceTest(1, 2, 3);
 
    // error incompatible types
 
}
//---------------++
void PassByReferenceTest(int &out1, int &out2, int &outArray[])
{
    out1        = 1;
    out2        = 2;
    outArray[0] = 3;
    outArray[1] = 4;    
}
hm, I dont now why it dont work, because the declared variables all of the type int and the values I send are too.
  • #8
  • Jul 16, 2007 7:17am Jul 16, 2007 7:17am
No need to apologise for your english, but I must admit that I find your confusion inconsistent with your question

Anyhow, the deal is that you cannot give constants "(1,2,3)" as arguments when calling that function. Rather, you must there tell the variables that you want the function to affect. That is, the argument list should read like "(out1,out2,outArray)", and more precisely the call to the function (in the start() function) should read:
PHP Code
PassByReferenceTest(out1, out2, outArray);
Note that there is no need to have the same names of the variables used as arguments at the function call as the function parameters, but there's no need not to either.
  • #9
  • Jul 16, 2007 8:20am Jul 16, 2007 8:20am
  •  tesla
  • | Joined Oct 2006 | Status: Friendly Neighborhood Programmer | 533 Posts
Heino, you should google "pass by reference" to get an idea of how this works.


Think of it this way: when you declare a vaiable, you're creating a "box" where values can be stored. When you pass by reference, you're telling the function that it can change the values stored in that box.

So...
void doSomething(int& out1) {
out1 = 13;
}

int x = 5;
doSomething(x);

x now equals 13.


Would give more detailed example but on blackberry.
  • #10
  • Last Post: Jul 17, 2007 12:29pm Jul 17, 2007 12:29pm
Hello, now I have find my mistake and it work, I have, like you say, give int values before at the function and not variables, now I give variables and it works and my code is shorter with this way by return 2 or more values from a function, also thank you very much people.
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