What's the difference of [DllImport ....] with _declspec(dllimport)

[Ed]

Hello, dear all,

I often see these two import usage in the code. Both are the interface
to use the Dll library. I think they are the same.
Normally P/Invoke means using the [DllImport ....] to import the
dll. But I have some confusion about them.

1. Is the "_declspec(dllimport)" also one of the forms of P/Invoke?
2. From performance aspect, which way is more better?
3. What's the difference of them.


Thank you in advance!

 

[Carl Daniel [VC++ MVP]]

Hello, dear all,

I often see these two import usage in the code. Both are the interface
to use the Dll library. I think they are the same.
Normally P/Invoke means using the [DllImport ....] to import the
dll. But I have some confusion about them.

1. Is the "_declspec(dllimport)" also one of the forms of P/Invoke?

No. __declspec(dllimport) is a compiler directive that tells the compiler to
expect that the function so decorated will be satisfied by an import library
to be linked into the module. [DllImportAttribute] is a CLR attribute used
in managed (.NET) development that provides the mapping for P/Invoke to call
an external function. They're similar, it's true, but the first
(__declspec) has nothing to do with managed programming.

2. From performance aspect, which way is more better?

They're used for different purposes. If you have a choice (e.g. you're
writing managed C++), __declspec(dllimport) will never give worse
performance.

3. What's the difference of them.

See above.

-cd

 

[Ed]

Hello, dear all,

I often see these two import usage in the code. Both are the interface
to use the Dll library. I think they are the same.
Normally P/Invoke means using the [DllImport ....] to import the
dll. But I have some confusion about them.

1. Is the "_declspec(dllimport)" also one of the forms of P/Invoke?

No. __declspec(dllimport) is a compiler directive that tells the compiler to
expect that the function so decorated will be satisfied by an import library
to be linked into the module. [DllImportAttribute] is a CLR attribute used
in managed (.NET) development that provides the mapping for P/Invoke to call
an external function. They're similar, it's true, but the first
(__declspec) has nothing to do with managed programming.

2. From performance aspect, which way is more better?

They're used for different purposes. If you have a choice (e.g. you're
writing managed C++), __declspec(dllimport) will never give worse
performance.

3. What's the difference of them.

See above.

-cd

Thank you !