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

  • Thread starter Thread starter Ed
  • Start date Start date
E

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!
 
Ed said:
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?
Click to expand...

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?
Click to expand...

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.
Click to expand...

See above.

-cd
 
Ed said:
Hello, dear all,
Click to expand...
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.
Click to expand...
1. Is the "_declspec(dllimport)" also one of the forms of P/Invoke?
Click to expand...

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?
Click to expand...

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.
Click to expand...

See above.

-cd
Click to expand...

Thank you ! :-)
 
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