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digitalmars.D.learn - compile error while use `extern(C++, class)`

reply mogu <mogucpp 163.com> writes:
 From spec (Interfacing to C++) 
https://dlang.org/spec/cpp_interface.html:

```
When mapping a D class onto a C++ struct, use extern(C++, struct) 
to avoid linking problems with C++ compilers (notably MSVC) that 
distinguish between C++'s class and struct when mangling. 
Conversely, use extern(C++, class) to map a D struct onto a C++ 
class.
```

But this compiles error. Please help, thanks.
Aug 17 2016
parent reply Lodovico Giaretta <lodovico giaretart.net> writes:
On Thursday, 18 August 2016 at 01:06:29 UTC, mogu wrote:

 From spec (Interfacing to C++) 
 https://dlang.org/spec/cpp_interface.html:

 ```
 When mapping a D class onto a C++ struct, use extern(C++, 
 struct) to avoid linking problems with C++ compilers (notably 
 MSVC) that distinguish between C++'s class and struct when 
 mangling. Conversely, use extern(C++, class) to map a D struct 
 onto a C++ class.
 ```

 But this compiles error. Please help, thanks.


Which kind of error? An error message by the compiler? One by the 
linker? The compiler crashes?

If you don't tell us what happens exactly, and a simple example 
code that triggers the issue, we don't know what to do.

If your codebase is big and you don't manage to reduce it to a 
couple lines to show the error, you can try dustmite [1].

[1] https://github.com/CyberShadow/DustMite/wiki
Aug 18 2016
parent reply mogu <mogucpp 163.com> writes:
On Thursday, 18 August 2016 at 10:45:14 UTC, Lodovico Giaretta 
wrote:

 Which kind of error? An error message by the compiler? One by 
 the linker? The compiler crashes?


Compiler Error exactly. The minimal code is(dmd or ldc2 in ubuntu 
16.04 lts):
```
extern (C++, struct)
class A {}
```

Error: identifier expected for C++ namespace found 'struct' when 
expecting ')' declaration expected, not ')'
Aug 18 2016
parent reply Lodovico Giaretta <lodovico giaretart.net> writes:
On Thursday, 18 August 2016 at 11:11:10 UTC, mogu wrote:

 On Thursday, 18 August 2016 at 10:45:14 UTC, Lodovico Giaretta 
 wrote:

 Which kind of error? An error message by the compiler? One by 
 the linker? The compiler crashes?


 Compiler Error exactly. The minimal code is(dmd or ldc2 in 
 ubuntu 16.04 lts):
 ```
 extern (C++, struct)
 class A {}
 ```

 Error: identifier expected for C++ namespace found 'struct' 
 when expecting ')' declaration expected, not ')'


Which compiler version are you using? On DMD 2.071.0 this does 
not work. On nightly build it compiles without errors. So 
probably it is a feature that is present, but didn't ship yet. I 
suggest you download the latest beta or a nightly build from the 
site.
Aug 18 2016
next sibling parent pineapple <meapineapple gmail.com> writes:
On Thursday, 18 August 2016 at 11:43:03 UTC, Lodovico Giaretta 
wrote:

 On Thursday, 18 August 2016 at 11:11:10 UTC, mogu wrote:

 On Thursday, 18 August 2016 at 10:45:14 UTC, Lodovico Giaretta 
 wrote:

 Which kind of error? An error message by the compiler? One by 
 the linker? The compiler crashes?


 Compiler Error exactly. The minimal code is(dmd or ldc2 in 
 ubuntu 16.04 lts):
 ```
 extern (C++, struct)
 class A {}
 ```

 Error: identifier expected for C++ namespace found 'struct' 
 when expecting ')' declaration expected, not ')'


 Which compiler version are you using? On DMD 2.071.0 this does 
 not work. On nightly build it compiles without errors. So 
 probably it is a feature that is present, but didn't ship yet. 
 I suggest you download the latest beta or a nightly build from 
 the site.


Wouldn't this be more syntactically consistent if it were "Cpp" 
instead of "C++"?
Aug 18 2016
prev sibling parent reply Johan Engelen <j j.nl> writes:
On Thursday, 18 August 2016 at 11:43:03 UTC, Lodovico Giaretta 
wrote:

 On Thursday, 18 August 2016 at 11:11:10 UTC, mogu wrote:

 Compiler Error exactly. The minimal code is(dmd or ldc2 in 
 ubuntu 16.04 lts):
 ```
 extern (C++, struct)
 class A {}
 ```

 Error: identifier expected for C++ namespace found 'struct' 
 when expecting ')' declaration expected, not ')'


 Which compiler version are you using? On DMD 2.071.0 this does 
 not work.


Note: this does work with LDC 1.1.0 even though it is based on 
DMD 2.071.

https://github.com/ldc-developers/ldc/releases/tag/v1.1.0-beta2
Aug 18 2016
parent reply Lodovico Giaretta <lodovico giaretart.net> writes:
On Thursday, 18 August 2016 at 16:19:41 UTC, Johan Engelen wrote:

 On Thursday, 18 August 2016 at 11:43:03 UTC, Lodovico Giaretta 
 wrote:

 Which compiler version are you using? On DMD 2.071.0 this does 
 not work.


 Note: this does work with LDC 1.1.0 even though it is based on 
 DMD 2.071.

 https://github.com/ldc-developers/ldc/releases/tag/v1.1.0-beta2


Well, LDC 1.1.0 is based on DMD 2.071.1, while I tested the above 
code on asm.dlang.org with DMD 2.071.0, so maybe on DMD 2.071.1 
it works too. On nightly it works for sure.
So again nothing wrong here, just a matter of having the most 
recent compiler version.
Aug 18 2016
parent mogu <mogucpp 163.com> writes:
On Thursday, 18 August 2016 at 16:41:27 UTC, Lodovico Giaretta 
wrote:

 On Thursday, 18 August 2016 at 16:19:41 UTC, Johan Engelen 
 wrote:

 On Thursday, 18 August 2016 at 11:43:03 UTC, Lodovico Giaretta 
 wrote:

 Which compiler version are you using? On DMD 2.071.0 this 
 does not work.


 Note: this does work with LDC 1.1.0 even though it is based on 
 DMD 2.071.

 https://github.com/ldc-developers/ldc/releases/tag/v1.1.0-beta2


 Well, LDC 1.1.0 is based on DMD 2.071.1, while I tested the 
 above code on asm.dlang.org with DMD 2.071.0, so maybe on DMD 
 2.071.1 it works too. On nightly it works for sure.
 So again nothing wrong here, just a matter of having the most 
 recent compiler version.


No, i'm using the newest version of dmd/ldc2 (2.071.1/1.0.0) 
released.
Aug 18 2016