Calling C++ function in namespace from C# with DlImport, Entrypoint

Calling C++ function in namespace from C# with DlImport, Entrypoint

I have read several questions related to mine, but none of the multiple
answers worked for me.
I need to call a function from an unmanaged DLL. I have the 32 bit version
of the DLL in SysWow64 and the 64 bit version in system32. Anyway, I am
compiling for x86. I don't have the source for the DLL, so recompiling
with extern "C" is not an option.
The relevant parts of the include file for the DLL:
(...)
#include <string>
namespace SomeNamespace
{
(...)
typedef std::wstring STRING;
(...)
class SomeClass
{
(...)
static bool SomeFunc(const STRING& p1, bool p2);
(...)
}
}
When calling SomeFunc, I am getting an exception: "Can't found the entry
point named '?' in DllName.dll" (translation is mine, could be inexact).
My declaration in C#:
[System.Runtime.InteropServices.DllImport("DllName.dll",
CallingConvention = CallingConvention.Cdecl, EntryPoint =
"?SomeFunc@SomeClass@SomeNamespace@@SA_NABV?$basic_string@_WU?$char_traits@_W@std@@V?$allocator@_W@2@@std@@_N@Z")]
bool SomeFunc(string p1, bool p2);
I have also tried the following:
[System.Runtime.InteropServices.DllImport("DllName.dll", CallingConvention
= CallingConvention.Cdecl, EntryPoint = "#15")]
bool SomeFunc(string p1, bool p2);
15 is the function ordinal according to Depends, and the EntryPoint in the
first version is also obtained from Depends.
According to undname.exe, this is the original declaration of the function:
public: static bool __cdecl SomeFunc(class ?? :: ??
::Z::basic_string<wchar_t,str
uct std::char_traits<wchar_t>,class w::allocator<wchar_t>,td,bool> const
&, ?? )
throw( ?? )
It doesn't seem to be parsing it correctly; the bool should be a parameter
for FuncName, not a type parameter for basic_string. However, I'm not sure
if this is just a parsing error from undname.exe or something more
serious.
How can I fix it?