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extern (c)
Oct 11, 2023
Paul
Oct 11, 2023
Ferhat Kurtulmuş
Oct 11, 2023
user1234
Oct 11, 2023
Paul
Oct 11, 2023
user1234
Oct 11, 2023
Imperatorn
October 11, 2023
Gravatar of PaulPosted by PaulReply
Paul
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What does the extern (c) attribute(?) do?
Does it tell the compiler/linker to build the function like a C compiler would build a C function? If so what does that mean?
Does it tell the compiler/linker to let C functions know it exists? If so what does that mean?
Is it meant for the compiler or linker or both?

Thanks for any assistance.

October 11, 2023
Gravatar of Ferhat KurtulmuşPosted by Ferhat Kurtulmuş
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On Wednesday, 11 October 2023 at 12:36:58 UTC, Paul wrote:

>

What does the extern (c) attribute(?) do?
Does it tell the compiler/linker to build the function like a C compiler would build a C function? If so what does that mean?
Does it tell the compiler/linker to let C functions know it exists? If so what does that mean?
Is it meant for the compiler or linker or both?

Thanks for any assistance.

It is about name mangling. It prevents symbol names from using D's name mangling.

https://dlang.org/blog/2017/12/20/ds-newfangled-name-mangling/

October 11, 2023
Gravatar of user1234Posted by user1234
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On Wednesday, 11 October 2023 at 12:36:58 UTC, Paul wrote:

>

What does the extern (c) attribute(?) do?
Does it tell the compiler/linker to build the function like a C compiler would build a C function? If so what does that mean?
Does it tell the compiler/linker to let C functions know it exists? If so what does that mean?
Is it meant for the compiler or linker or both?

Thanks for any assistance.

extern(C) on module level functions affect the mangling and the calling convention.

  • Mangling is used by the linker to link symbols between objects.
  • Calling convention affects the compiler backend in how code is generated for a CALL instruction.
October 11, 2023
Gravatar of PaulPosted by Paul
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On Wednesday, 11 October 2023 at 12:54:53 UTC, user1234 wrote:

>

extern(C) on module level functions affect the mangling and the calling convention.

  • Mangling is used by the linker to link symbols between objects.
  • Calling convention affects the compiler backend in how code is generated for a CALL instruction.

So C doesn't use name mangling and extern (C) in a D prog would turn off D mangling thereby allowing C and D object files to be linked together?

I didn't know C and D had different calling conventions...i.e. different ABI's?

October 11, 2023
Gravatar of user1234Posted by user1234
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On Wednesday, 11 October 2023 at 13:36:16 UTC, Paul wrote:

>

On Wednesday, 11 October 2023 at 12:54:53 UTC, user1234 wrote:

>

extern(C) on module level functions affect the mangling and the calling convention.

  • Mangling is used by the linker to link symbols between objects.
  • Calling convention affects the compiler backend in how code is generated for a CALL instruction.

So C doesn't use name mangling

I see what you mean. I just consider no mangling as a kind of mangling, that is "just the symbol name".

>

and extern (C) in a D prog would turn off D mangling thereby allowing C and D object files to be linked together?

I didn't know C and D had different calling conventions...i.e. different ABI's?

They are mostly similar but according to https://dlang.org/spec/abi.html#function_calling_conventions there are differences.

October 11, 2023
Gravatar of ImperatornPosted by Imperatorn
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On Wednesday, 11 October 2023 at 13:36:16 UTC, Paul wrote:

>

On Wednesday, 11 October 2023 at 12:54:53 UTC, user1234 wrote:

>

extern(C) on module level functions affect the mangling and the calling convention.

  • Mangling is used by the linker to link symbols between objects.
  • Calling convention affects the compiler backend in how code is generated for a CALL instruction.

So C doesn't use name mangling and extern (C) in a D prog would turn off D mangling thereby allowing C and D object files to be linked together?

I didn't know C and D had different calling conventions...i.e. different ABI's?

https://dlang.org/spec/abi.html