Difference between revisions of "Documentation/DevGuide/ProUNO/Bridge/Return Values"

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(Initial author Sun Microsystems, Inc.)
 
 
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|NextPage=Documentation/DevGuide/ProUNO/Bridge/Usage of Types
 
|NextPage=Documentation/DevGuide/ProUNO/Bridge/Usage of Types
 
}}
 
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{{Documentation/DevGuideLanguages|Documentation/DevGuide/ProUNO/Bridge/{{SUBPAGENAME}}}}
 
{{DISPLAYTITLE:Return Values}}
 
{{DISPLAYTITLE:Return Values}}
 
There are three possible ways to return values in UNO:
 
There are three possible ways to return values in UNO:
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To receive a return value in C++ provide a <code>VARIANT</code> argument to <code>IDispatch::Invoke:</code>
 
To receive a return value in C++ provide a <code>VARIANT</code> argument to <code>IDispatch::Invoke:</code>
−
 
+
<syntaxhighlight lang="idl">
 
   //UNO IDL
 
   //UNO IDL
 
   long func();
 
   long func();
−
 
+
</syntaxhighlight>
−
   //
+
<syntaxhighlight lang="cpp"> 
 +
   //C++
 
     DISPPARAMS dispparams= { NULL, 0, 0, 0};  
 
     DISPPARAMS dispparams= { NULL, 0, 0, 0};  
 
     VARIANT result;  
 
     VARIANT result;  
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     hr= pdisp->Invoke( dispid, IID_NULL, LOCALE_USER_DEFAULT, DISPATCH_METHOD,  
 
     hr= pdisp->Invoke( dispid, IID_NULL, LOCALE_USER_DEFAULT, DISPATCH_METHOD,  
 
                             &dispparams, &result, NULL, 0);  
 
                             &dispparams, &result, NULL, 0);  
 +
</syntaxhighlight>
  
−
The following example shows using VB and JScript this is simple:
+
The following examples show that using VB or JScript is simple:
−
 
+
<syntaxhighlight lang="vb">
−
   //VB
+
   ' VB
 
   Dim result As Long
 
   Dim result As Long
 
   result= obj.func
 
   result= obj.func
−
 
+
</syntaxhighlight>
 +
 
 +
<syntaxhighlight lang="javascript">
 
   //JScript
 
   //JScript
 
   var result= obj.func
 
   var result= obj.func
 +
</syntaxhighlight>
  
 
When a function has inout parameters then provide arguments by reference in C++:
 
When a function has inout parameters then provide arguments by reference in C++:
−
 
+
<syntaxhighlight lang="idl">
 
   //UNO IDL
 
   //UNO IDL
 
   void func( [inout] long val);
 
   void func( [inout] long val);
−
 
+
</syntaxhighlight>
 +
<syntaxhighlight lang="cpp"> 
 
   //C++
 
   //C++
 
   long longOut= 10;
 
   long longOut= 10;
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   //The value of longOut will be modified by UNO function.
 
   //The value of longOut will be modified by UNO function.
 +
</syntaxhighlight>
  
−
The above VB code is written like this, because VB uses call by reference by default. After the call to <code>func()</code>, value contains the function output:
+
The VB code below is simple because VB uses call by reference by default. After the call to <code>func()</code>, value contains the function output:
−
 
+
<syntaxhighlight lang="vb">
 
   Dim value As Long
 
   Dim value As Long
 
   value= 10
 
   value= 10
 
   obj.func value
 
   obj.func value
−
 
+
</syntaxhighlight>
 
The type of argument corresponds to the UNO type according to the default mapping, cf . [[Documentation/DevGuide/ProUNO/Bridge/Type Mappings|Type Mappings]]. If in doubt, use <code>VARIANT</code>s.
 
The type of argument corresponds to the UNO type according to the default mapping, cf . [[Documentation/DevGuide/ProUNO/Bridge/Type Mappings|Type Mappings]]. If in doubt, use <code>VARIANT</code>s.
−
 
+
<syntaxhighlight lang="vb">
 
   Dim value As Variant
 
   Dim value As Variant
 
   value= 10;
 
   value= 10;
 
   obj.func value
 
   obj.func value
−
 
+
</syntaxhighlight>
 
However, there is one exception. If a function takes a character (<code>char</code>) as an argument and is called from VB, use an <code>Integer</code>, because there is no character type in VB. For convenience, the COM bridge also accepts a String as <code>inout</code> and <code>out</code> parameter:
 
However, there is one exception. If a function takes a character (<code>char</code>) as an argument and is called from VB, use an <code>Integer</code>, because there is no character type in VB. For convenience, the COM bridge also accepts a String as <code>inout</code> and <code>out</code> parameter:
−
 
+
<syntaxhighlight lang="vb">
−
   //VB
+
   ' VB
 
   Dim value As String
 
   Dim value As String
 
   // string must contain only one character
 
   // string must contain only one character
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   Dim ret As String
 
   Dim ret As String
 
   obj.func value
 
   obj.func value
 +
</syntaxhighlight>
  
 
JScript does not have <code>inout</code> or <code>out</code> parameters. As a workaround, the bridge accepts JScript <code>Array</code> objects. Index 0 contains the value.
 
JScript does not have <code>inout</code> or <code>out</code> parameters. As a workaround, the bridge accepts JScript <code>Array</code> objects. Index 0 contains the value.
−
 
+
<syntaxhighlight lang="javascript">
 
   // Jscript
 
   // Jscript
 
   var inout= new Array();
 
   var inout= new Array();
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   obj.func( inout);
 
   obj.func( inout);
 
   var value= inout[0];
 
   var value= inout[0];
−
 
+
</syntaxhighlight>
 
Out parameters are similar to <code>inout</code> parameters in that the argument does not need to be initialized.
 
Out parameters are similar to <code>inout</code> parameters in that the argument does not need to be initialized.
−
 
+
<syntaxhighlight lang="cpp">
 
   //C++
 
   //C++
 
   long longOut;
 
   long longOut;
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   hr= pdisp->Invoke( dispid, IID_NULL, LOCALE_USER_DEFAULT, DISPATCH_METHOD,
 
   hr= pdisp->Invoke( dispid, IID_NULL, LOCALE_USER_DEFAULT, DISPATCH_METHOD,
 
                   &dispparams, NULL, NULL, 0);
 
                   &dispparams, NULL, NULL, 0);
−
 
+
</syntaxhighlight>
−
   //VB
+
 
 +
<syntaxhighlight lang="vb">
 +
   ' VB
 
   Dim value As Long
 
   Dim value As Long
 
   obj.func value
 
   obj.func value
−
 
+
</syntaxhighlight>
 +
 
 +
<syntaxhighlight lang="javascript">
 
   //JScript
 
   //JScript
 
   var out= new Array();
 
   var out= new Array();
 
   obj.func(out);
 
   obj.func(out);
 
   var value= out[0];
 
   var value= out[0];
 +
</syntaxhighlight>
  
 +
{{PDL1}}
  
−
{{PDL1}}
+
[[Category:Documentation/Developer's Guide/Professional UNO]]
−
[[Category: Professional UNO]]
 

Latest revision as of 14:04, 23 December 2020



There are three possible ways to return values in UNO:

  • function return values
  • inout parameters
  • out parameters

Return values are commonplace in most languages, whereas inout and out parameters are not necessarily supported. For example, in JScript.

To receive a return value in C++ provide a VARIANT argument to IDispatch::Invoke: 

  //UNO IDL
  long func();

  
  //C++
    DISPPARAMS dispparams= { NULL, 0, 0, 0}; 
    VARIANT result; 
    VariantInit( &result); 
    hr= pdisp->Invoke( dispid, IID_NULL, LOCALE_USER_DEFAULT, DISPATCH_METHOD, 
                             &dispparams, &result, NULL, 0);

The following examples show that using VB or JScript is simple: 

  ' VB
  Dim result As Long
  result= obj.func

  //JScript
  var result= obj.func

When a function has inout parameters then provide arguments by reference in C++: 

  //UNO IDL
  void func( [inout] long val);

  
  //C++
  long longOut= 10;
  VARIANT var;
  VariantInit(&var);
  var.vt= VT_BYREF | VT_I4;
  var.plVal= &longOut;
  
  DISPPARAMS dispparams= { &var, 0, 1, 0}; 
  hr= pdisp->Invoke( dispid, IID_NULL, LOCALE_USER_DEFAULT, DISPATCH_METHOD,
                  &dispparams, NULL, NULL, 0);
  
  //The value of longOut will be modified by UNO function.

The VB code below is simple because VB uses call by reference by default. After the call to func(), value contains the function output: 

  Dim value As Long
  value= 10
  obj.func value

The type of argument corresponds to the UNO type according to the default mapping, cf . Type Mappings. If in doubt, use VARIANTs. 

  Dim value As Variant
  value= 10;
  obj.func value

However, there is one exception. If a function takes a character (char) as an argument and is called from VB, use an Integer, because there is no character type in VB. For convenience, the COM bridge also accepts a String as inout and out parameter: 

  ' VB
  Dim value As String
  // string must contain only one character
  value= "A"
  Dim ret As String
  obj.func value

JScript does not have inout or out parameters. As a workaround, the bridge accepts JScript Array objects. Index 0 contains the value. 

  // Jscript
  var inout= new Array();
  inout[0]=123;
  obj.func( inout);
  var value= inout[0];

Out parameters are similar to inout parameters in that the argument does not need to be initialized. 

  //C++
  long longOut;
  VARIANT var;
  VariantInit(&var);
  var.vt= VT_BYREF | VT_I4;
  var.plVal= &longOut;
  
  DISPPARAMS dispparams= { &var, 0, 1, 0}; 
  hr= pdisp->Invoke( dispid, IID_NULL, LOCALE_USER_DEFAULT, DISPATCH_METHOD,
                  &dispparams, NULL, NULL, 0);

  ' VB
  Dim value As Long
  obj.func value

  //JScript
  var out= new Array();
  obj.func(out);
  var value= out[0];
Content on this page is licensed under the Public Documentation License (PDL).
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