Return a string from C++ Native to C# 64-bit

[jimbrown]

This works in VS2008 for 32-bit projects but fails for 64-bit
projects. How do I return a result that C# will interpret as a
string?

C#
[DllImport("hello.dll", CharSet = CharSet.Ansi)]
private static extern string getAString();

String xx = getAString();

C++ in "hello.dll"
extern "C" {
__declspec(dllexport) unsigned char * getAString()
{
printf("call made\n");
return (unsigned char *)"a string";
}
}

 

[Göran Andersson]

This works in VS2008 for 32-bit projects but fails for 64-bit
projects. How do I return a result that C# will interpret as a
string?

C#
[DllImport("hello.dll", CharSet = CharSet.Ansi)]
private static extern string getAString();

String xx = getAString();

C++ in "hello.dll"
extern "C" {
__declspec(dllexport) unsigned char * getAString()
{
printf("call made\n");
return (unsigned char *)"a string";
}
}

What exactly do you mean when you say that it "fails"? What happens, and
how does that differ from what you expect? Do you get any error message?

 

[Franck]

This works in VS2008 for 32-bit projects but fails for 64-bit
projects.  How do I return a result that C# will interpret as a
string?

C#
            [DllImport("hello.dll", CharSet = CharSet.Ansi)]
            private static extern string getAString();

                    String xx = getAString();

C++ in "hello.dll"
   extern "C" {
   __declspec(dllexport) unsigned char * getAString()
   {
        printf("call made\n");
        return (unsigned char *)"a string";
   }
   }

easy one.
32 DLL don't work properly on 64bits development.
You will have problems as long as your DLL is 32bit Using 64bits DLL
solve all my issues.
From what i experienced the applications i'm making seems to call DLL
as 64bits and ask for 64bits answer,
since the return value is 32bits the memory (here i guess) classified
the return as bogus and incomplete

But like i said, building the DLL as 64bits solve my issue.

In your case, i guess you will need to pass a 64bit string

i C# a 64bit string is using string builder with 64bit int limits
like :
StringBuilder sb = new StringBuilder(Int64.MaxValue, Int64.MinValue);

 

[Göran Andersson]

In your case, i guess you will need to pass a 64bit string

i C# a 64bit string is using string builder with 64bit int limits
like :
StringBuilder sb = new StringBuilder(Int64.MaxValue, Int64.MinValue);

A 64 bit string? What are you talking about?

The C++ code returns a byte array that contains a string that is encoded
as Ansi (Encoding.Default). This is decoded into a unicode string by the
marshalling code. A string in .NET looks the same regardless if it's on
a 32 bit platform or a 64 bit platform.

 

[jimbrown]

A 64 bit string? What are you talking about?

The C++ code returns a byte array that contains a string that is encoded
as Ansi (Encoding.Default). This is decoded into a unicode string by the
marshalling code. A string in .NET looks the same regardless if it's on
a 32 bit platform or a 64 bit platform.

The error I get is a complete failure of the debugger "vshost.exe" has
stopped working. I assume it is a problem with the marshalling code.

 

[Ben Voigt [C++ MVP]]

This works in VS2008 for 32-bit projects but fails for 64-bit
projects. How do I return a result that C# will interpret as a
string?

C#
[DllImport("hello.dll", CharSet = CharSet.Ansi)]
private static extern string getAString();

String xx = getAString();

C++ in "hello.dll"
extern "C" {
__declspec(dllexport) unsigned char * getAString()
{
printf("call made\n");
return (unsigned char *)"a string";
}
}

easy one.
32 DLL don't work properly on 64bits development.

This is correct. You need to compile your C++ code with the 64-bit
compiler, no changes needed to the code.

You will have problems as long as your DLL is 32bit Using 64bits DLL
solve all my issues.
From what i experienced the applications i'm making seems to call DLL
as 64bits and ask for 64bits answer,
since the return value is 32bits the memory (here i guess) classified
the return as bogus and incomplete

But like i said, building the DLL as 64bits solve my issue.

But everything after this is totally bogus.