Empty strings are initialized like this:. A null string does not refer to an instance of a System. String object and any attempt to call a method on a null string results in a NullReferenceException. In the above code we created a string Object and assigned Nothing and next we check the string is null or not. IsNullOrEmpty is a convenience method that enables you to simultaneously test whether a String is Nothing or its value is Empty.
It is equivalent to the following code:. NullReferenceException indicates that you are trying to access member fields, or function types, on an object reference that points to null.
That means the reference to an Object which is not initialized. More about Home C VB. How to VB. Privacy policy. Both the System. String and System. StringBuilder classes have similar marshaling behavior. The following table shows the marshaling options for the string data type when marshaled as a method argument to unmanaged code. This table applies to String. For StringBuilder , the only options allowed are UnmanagedType.
LPStr and UnmanagedType. LPWSTR ] and the string is passed by value not ref or out , the string is pinned and used directly by native code. Otherwise, platform invoke copies string arguments, converting from the. NET Framework format Unicode to the platform unmanaged format.
Strings are immutable and are not copied back from unmanaged memory to managed memory when the call returns. Native code is only responsible for releasing the memory when the string is passed by reference and it assigns a new value. Otherwise, the. NET runtime owns the memory and will release it after the call. The following table lists the marshaling options for strings when marshaled as a method argument of a platform invoke call.
The MarshalAsAttribute attribute provides several UnmanagedType enumeration values to marshal strings. The following type definition shows the correct use of MarshalAsAttribute for platform invoke calls. Archived Forums V. Visual Basic Language. Not for VB6 2 1.
Sign in to vote. I am trying to use the StdRegProv. It requires an array type object and I'm having trouble providing it such a value. Dim dcomProtocols As System. Array "" doesn't work Dim dcomProtocols As System. If a VB. NET equivalent of the Array method from VBScript exists that would be better since I don't need to waste lines declaring and initializing a variable.
Tuesday, November 11, PM. Thanks to all of you for the help and a special thanks to Chris Dunaway who pointed me in the right direction.
NET Imports Microsoft. LocalMachine, " Wednesday, November 12, PM. Just tried it. No runtime errors for type mismatching, but the function call fails, the existing value doesn't get overwritten. Is this an error message? There's no error message, but there's also no effect. The goal is to overwrite an existing registry value with nothing. A null string like "". The problem is that it's not just a string, it's an array of strings. Visual Basic, however, takes care of adding the final terminating null when we pass the string by value".
Proposed as answer by konikula Wednesday, November 12, AM. Object , ByVal e As System. EventArgs Handles MyBase. Wednesday, November 12, AM. Could System. IntPtr to Array differ from direct calling api with Array as argument? Proposed as answer by konikula Wednesday, November 12, PM. I am using Visual Studio with Visual Basic. NET I am trying to set it to NULL. John Anthony Oliver I tried doing this with just a one element array since I don't need 10 elements, or any elements really, just all NULL but that didn't work.
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