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- Checks performed
- Managing the errors
- Parameters that must be passed to the method of DLL
- Passing a string to a DLL or retrieving a string from a DLL
- Passing a structure containing a string to a DLL
- Procedure called in CallBack
- Miscellaneous
CallInterface (Function) In french: AppelInterface Runs a method of an interface of an object implemented in a DLL external to the WINDEV framework. This object can be a C++ object or a COM object.
nAllocator is system int
API("ole32", "CoGetMalloc", 1, &nAllocator)
nMemory is system int = CallInterface(nAllocator, 3, 1024)
Syntax
Using the method number Hide the details
<Result> = CallInterface(<Object address> , <Method number> [, <Parameter 1> [... [, <Parameter N>]]])
<Result>: 4-byte integer in 32 bits, 8-byte integer in 64 bits Result of method execution. This result can be an error code. The type of this result depends on the method run. For more details, see the documentation about the method.
The method result will not be retrieved if its size exceeds the size of the integer defined for the platform. <Object address>: System integer Address of object onto which a method will be called. In most cases, this address is the result of the previous call to an API. <Method number>: Integer Order number of method in the table of virtual methods.
CAUTION:
- the order number takes the base classes into account
- the order number starts from 0.
<Parameter 1>: Type corresponding to the parameter First parameter that will be passed to the method. These parameters and the parameters expected by the method must have the same type. Can be used: - the "simple" types (see the Remarks),
- the structures (see the Remarks),
- a name of WLanguage procedure. This procedure will be called by the method (see the Remarks).
<Parameter N>: Type corresponding to the parameter Nth parameter that will be passed to the method. These parameters and the parameters expected by the method must have the same type. Can be used: - the "simple" types (see the Remarks),
- the structures (see the Remarks),
- a name of WLanguage procedure. This procedure will be called by method (see the Remarks).
Using an API Description variable Hide the details
<Result> = CallInterface(<Object address> , <API to run> [, <Parameter 1> [... [, <Parameter N>]]])
<Result>: 4-byte integer in 32 bits, 8-byte integer in 64 bits Result of method execution. This result can be an error code. The type of this result depends on the method run. For more details, see the documentation about the method.
The method result will not be retrieved if its size exceeds the size of the integer defined for the platform. <Object address>: System integer Address of object onto which a method will be called. In most cases, this address is the result of the previous call to an API. <API to run>: API Description variable API description variable containing the characteristics of the method to be run. <Parameter 1>: Type corresponding to the parameter First parameter that will be passed to the method. These parameters and the parameters expected by the method must have the same type. Can be used: - the "simple" types (see the Remarks),
- the structures (see the Remarks),
- a name of WLanguage procedure. This procedure will be called by the method (see the Remarks).
<Parameter N>: Type corresponding to the parameter Nth parameter that will be passed to the method. These parameters and the parameters expected by the method must have the same type. Can be used: - the "simple" types (see the Remarks),
- the structures (see the Remarks),
- a name of WLanguage procedure. This procedure will be called by method (see the Remarks).
Remarks CallInterface is protected against the "General protection faults" in the method called. Nevertheless, a WLanguage error is triggered if this type of error occurs. When running methods, if the result returned corresponds to an error, use ErrorInfo (associated with the errSystemCode or errSystemMessage constant) to get more details on the error. Parameters that must be passed to the method of DLL These parameters and the parameters expected by the method must have the same type. The available types are as follows: - The "simple" types (integer, real and boolean). Using another WLanguage type triggers a WLanguage error.
If the method to run expects a Windows pointer or handle, use a system integer.
If the method to run expects an address, use the & operator. - The "string" types.
- The structure types.
- A name of WLanguage procedure. This procedure will be called by the method of the DLL (see the paragraph below).
The parameters depend on the method run. For more details, see the documentation about this method.
Passing a string to a DLL or retrieving a string from a DLL - In input parameter, use the string type. For example:
sString is string
CallInterface(<Object address>, <Method number>, sString)
- In output parameter, the C language cannot easily manage the dynamic strings. Therefore, you must:
- define a maximum size, with the "String on" type. For example:
sString is string on 100
CallInterface(<Object address>, <Method number>, sString)
// in Method in C:
// STRNCPY(PointerInC, "Test", 100)
- retrieve the addresses of strings in C (however, in this case, the code section in C must "preserve" the strings returned), then transfer the string into a string variable with StringRetrieve. For example:
nStringAddress is system int
API(<Object address>, <Method number>, &nStringAddress)
sString is string
sString = StringRetrieve(nStringAddress, srASCIIZAddress)
// in Method in C: *PointerInC = "Test"
- In return value, retrieve the addresses of strings in C (however, in this case, the code section in C must "preserve" the strings returned), then transfer the string into a string variable with StringRetrieve. For example:
nStringAddress is system int
nStringAddress = CallInterface(<Object address>, <Method number>)
sString is string
sString = StringRetrieve(nStringAddress, srASCIIZAddress)
// in Method in C: Return PointerInC
Passing a structure containing a string to a DLL - In input, the following code must be used:
Struct is structure
sString is string
END
AStruct is Struct
CallInterface(<Object address>, <Method number>, &AStruct)
- In output, the C language does not easily manage the dynamic strings. Therefore, you must:
- define a maximum size and perform a copy into the WLanguage memory. For example:
sString is string on 100
Struct is structure
aString is int
END
AStruct is Struct
AStruct:aString = &sString
CallInterface(<Object address>, <Method number>, &AStruct)
// in Method in C:
// STRNCPY(CStruct->PointerInC, "Test", 100)
- retrieve the address of strings in C (however, in this case, the code section in C must "preserve " the strings returned). For example:
sString is string
Struct is structure
aString is int
END
AStruct is Struct
CallInterface(<Object address>, <Method number>, &AStruct)
sString = StringRetrieve(AStruct:aString, srASCIIZAddress )
// in Method in C: StructInC->PointerInC = "Test"
Procedure called in CallBack Some methods expect the address of a "Callback" procedure as parameter: this procedure will be called back by the DLL method. To use a callback procedure in WLanguage: 1. Create the callback procedure in your project To retrieve the parameters, you must exactly describe the parameters expected by the "CallBack" function. Otherwise, "general protection faults" may occur.
PROCEDURE <Procedure name> (<Param1> is <Type1>, ... <Param2> is <Type2>)
Remarks: - The types must correspond to the ones described in the documentation of the DLL.
- The parameters must necessarily be passed by value. To retrieve a parameter by reference:
- Use an integer.
- With Transfer, retrieve or assign the real value.
2. Modify the call to the method accordingly. Use the following syntax:
CallInterface(<Object address>, <Method number>, ...
&<Name of CallBack procedure>)
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