I'm linking D with C++ lib.a file.  When the C++ function has compatible data types I can call them from D.  But when I changed the parameter to string I got bunch of errors.

Data Type Compatibility table does not include strings.  Is there a way of passing strings?

On Tuesday, 30 July 2013 at 19:52:44 UTC, Milvakili wrote:
> I'm linking D with C++ lib.a file.  When the C++ function has compatible data types I can call them from D.  But when I changed the parameter to string I got bunch of errors.
>
> Data Type Compatibility table does not include strings.  Is there a way of passing strings?

http://dlang.org/phobos/std_string.html#.toStringz

On Tuesday, 30 July 2013 at 20:02:51 UTC, Dicebot wrote:
> On Tuesday, 30 July 2013 at 19:52:44 UTC, Milvakili wrote:
>> I'm linking D with C++ lib.a file.  When the C++ function has compatible data types I can call them from D.  But when I changed the parameter to string I got bunch of errors.
>>
>> Data Type Compatibility table does not include strings.  Is there a way of passing strings?
>
> http://dlang.org/phobos/std_string.html#.toStringz


So I need to pass them as char*, I can not pass them as string?

On Tuesday, 30 July 2013 at 20:09:01 UTC, Milvakili wrote:
> On Tuesday, 30 July 2013 at 20:02:51 UTC, Dicebot wrote:
>> On Tuesday, 30 July 2013 at 19:52:44 UTC, Milvakili wrote:
>>> I'm linking D with C++ lib.a file.  When the C++ function has compatible data types I can call them from D.  But when I changed the parameter to string I got bunch of errors.
>>>
>>> Data Type Compatibility table does not include strings.  Is there a way of passing strings?
>>
>> http://dlang.org/phobos/std_string.html#.toStringz
>
>
> So I need to pass them as char*, I can not pass them as string?

Correct.

Just thinking off the top of my head: you could probably hack something together though with a struct and casting.

On Tuesday, 30 July 2013 at 20:17:34 UTC, John Colvin wrote:
> On Tuesday, 30 July 2013 at 20:09:01 UTC, Milvakili wrote:
>> On Tuesday, 30 July 2013 at 20:02:51 UTC, Dicebot wrote:
>>> On Tuesday, 30 July 2013 at 19:52:44 UTC, Milvakili wrote:
>>>> I'm linking D with C++ lib.a file.  When the C++ function has compatible data types I can call them from D.  But when I changed the parameter to string I got bunch of errors.
>>>>
>>>> Data Type Compatibility table does not include strings.  Is there a way of passing strings?
>>>
>>> http://dlang.org/phobos/std_string.html#.toStringz
>>
>>
>> So I need to pass them as char*, I can not pass them as string?
>
> Correct.
>
> Just thinking off the top of my head: you could probably hack something together though with a struct and casting.

Thanks.  Is there any work in progress related to string passing?
I think string passing should be solved automatically.

Coz otherwise one need to write wrapper for each c++ function that has a string parameter.

thanks.

On Tuesday, 30 July 2013 at 20:09:01 UTC, Milvakili wrote:
> So I need to pass them as char*, I can not pass them as string?

I would pass it as a char* and a size_t for length.

extern(C++) void cpp_func(char* strptr, size_t strlen);


void main() {
   string foo = "test";
   cpp_func(foo.ptr, foo.length);
}


It'd be important on the C++ side to remember that it is NOT zero terminated, and always use that length parameter instead of normal C functions.

But that'd give the most efficiency, since that's using the same representation as D itself.

On Tuesday, 30 July 2013 at 20:22:46 UTC, Milvakili wrote:
> Thanks.  Is there any work in progress related to string passing?
> I think string passing should be solved automatically.
>
> Coz otherwise one need to write wrapper for each c++ function that has a string parameter.
>
> thanks.

c_function(toStringz("hello").ptr) does not seem that bad, what is the issue here?

On Tuesday, 30 July 2013 at 20:09:01 UTC, Milvakili wrote:

> So I need to pass them as char*, I can not pass them as string?

C++ doesn't have an immutable(char)[], it has char* and its own string class. To communicate with it one must choose a type both languages can understand, char* is that. D may be able to get away with providing a C++ string, but I'm not familiar with the integration layer.

On Tuesday, 30 July 2013 at 20:09:01 UTC, Milvakili wrote:
> On Tuesday, 30 July 2013 at 20:02:51 UTC, Dicebot wrote:
>> On Tuesday, 30 July 2013 at 19:52:44 UTC, Milvakili wrote:
>>> I'm linking D with C++ lib.a file.  When the C++ function has compatible data types I can call them from D.  But when I changed the parameter to string I got bunch of errors.
>>>
>>> Data Type Compatibility table does not include strings.  Is there a way of passing strings?
>>
>> http://dlang.org/phobos/std_string.html#.toStringz
>
>
> So I need to pass them as char*, I can not pass them as string?

You can't pass them as string because they have different representations. A C++ string is null terminated while a D string is not. If you pass a D string to C++ then it will not have the same length and give undesirable behavior.

If you really want to use strings, then wrap each C++ function with one that converts the string to a C string. If D used both pascal and C++ style strings as one(a waste of 1 extra byte per string) then life would be easier.

On Tuesday, 30 July 2013 at 20:22:46 UTC, Milvakili wrote:
> On Tuesday, 30 July 2013 at 20:17:34 UTC, John Colvin wrote:
>> On Tuesday, 30 July 2013 at 20:09:01 UTC, Milvakili wrote:
>>> On Tuesday, 30 July 2013 at 20:02:51 UTC, Dicebot wrote:
>>>> On Tuesday, 30 July 2013 at 19:52:44 UTC, Milvakili wrote:
>>>>> I'm linking D with C++ lib.a file.  When the C++ function has compatible data types I can call them from D.  But when I changed the parameter to string I got bunch of errors.
>>>>>
>>>>> Data Type Compatibility table does not include strings.  Is there a way of passing strings?
>>>>
>>>> http://dlang.org/phobos/std_string.html#.toStringz
>>>
>>>
>>> So I need to pass them as char*, I can not pass them as string?
>>
>> Correct.
>>
>> Just thinking off the top of my head: you could probably hack something together though with a struct and casting.
>
> Thanks.  Is there any work in progress related to string passing?
> I think string passing should be solved automatically.
>
> Coz otherwise one need to write wrapper for each c++ function that has a string parameter.
>
> thanks.

I had a crack at making this work, but I'm stuck on some basics and I don't know a great deal about c++ really

//inter.cpp
#include<string>
#include<iostream>
using namespace std;

void printString(string* s)
{
    cout << s << "\n";
}

string *strD2Cpp(char *ptr, unsigned long long length)
{
    return new std::string(ptr, length);
}

//inter.d
extern(C++)
{
    interface CppString{}
    CppString strD2Cpp(char* ptr, size_t length);
    void printString(CppString s);
}

void main()
{
    string s = "2432qreafdsa";
    auto s_cpp = strD2Cpp(s.dup.ptr, s.length);
    printString(s_cpp);
}

$ dmd -c -m64 inter.d
$ g++ -c -m64 inter.cpp -ointercpp.o
$ g++ inter.o intercpp.o -ointer -lphobos2
inter.o: In function `_Dmain':
inter.d:(.text._Dmain+0x48): undefined reference to `printString(CppString*)'
collect2: error: ld returned 1 exit status


Is this an incompatibility between dmd and g++? I'm on linux x64

How come it's happy to have CppString as the return type of strD2Cpp but not as a parameter to printString?

Also, using size_t in inter.cpp caused linker errors, hence the unsigned long long.