• CallDLL32 is protected against "General Protection Faults" in the function called. Nevertheless, a WLanguage error is triggered if this type of error occurs.
• For the functions following the PASCAL call prototype (especially the functions of the Windows API), a simple check on the number of parameters passed to the function is performed. A WLanguage error occurs in case of discrepancy.

Managing errors

Loading and unloading the DLL

Parameters that will be passed to the function of DLL

• The "simple" types (integer, real and boolean). Using another WLanguage type triggers a WLanguage error.
  If the function to run expects a pointer or a Windows handle, use a system integer.
  If the function 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 function of the DLL (see the paragraph below).
  The parameters depend on the function run. See the documentation about this function for more details.

Passing a string to an API or retrieving a string from an API

1. In input parameter, use the string type. For example:
   
   sString is string
   CallDll32(<DLL>, <Function>, sString)
2. 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
     CallDLL32(<DLL>, <Function>, 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
     CallDLL32(<DLL>, <Function>, &nStringAddress)
     sString is string
     sString = StringRetrieve(nStringAddress, srASCIIZAddress)
     // in Method in C: *PointerInC = "Test"
3. 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 = CallDLL32(<DLL>, <Function>)
   sString is string
   sString = StringRetrieve(nStringAddress, srASCIIZAddress)
   // in Method in C: Return PointerInC

Passing a structure containing a string to an API

1. In input, the following code must be used:
   
   Struct is structure
   sString is string
   END
   AStruct is Struct
   CallDLL32(<DLL>, <Function>, &AStruct)
2. 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
     CallDLL32(<DLL>, <Function>, &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
     CallDLL32(<DLL>, <Function>, &AStruct)
     sString = StringRetrieve(AStruct:aString, srASCIIZAddress)
     // in Method in C: StructInC->PointerInC = "Test"

Procedure called in CallBack

• The types must correspond to the ones described in the documentation of the API.
• The type of the "CallBack" function of the DLL must be "stdcall".
• The parameters must necessarily be passed by value. To retrieve a parameter by reference:
  1. Use an integer.
  2. With Transfer, retrieve or assign the real value.

Miscellaneous

• API and CallDLL32 do not lock the other threads.
• If the API function called modifies the system regional settings, the previous regional settings are restored.

• API and CallDLL32 lock the other threads.
• If the API function called modifies the system regional settings (languages, decimal places, etc.), the previous regional settings are not restored.