I have the below C struct that has a couple nested structures that have proven to be difficult to deal with using my knowledge of SWIG. Everything below is easily wrapped by SWIG execept for saddr (C socket address) and mac[6] (C array representing a MAC address). Since SWIG gives me the pointer value (SWIGTYPE_p_unsigned_char and SWIGTYPE_p_sockaddr), I would like to somehow call a helper C function to convert the pointer to a char*. I have the helper function, but I don't know the best way to plug this into SWIG. Is there any way to configure the getMac() and getSaddr() to call the helper function?
C Structure Trying To Wrap:
%rename (Details) details_t_;
typedef struct details_t_ {
uint16_t code;
char *name;
**sockaddr *saddr;**
uint32_t saddr_len;
uint8_t flag;
ios_boolean is_child;
**unsigned char mac[6];**
} details_t;
Generated Java Code:
public void setMac(SWIGTYPE_p_unsigned_char value) {
TestJNI.Details_mac_set(swigCPtr, this, SWIGTYPE_p_unsigned_char.getCPtr(value));
}
public SWIGTYPE_p_unsigned_char getMac() {
long cPtr = TestJNI.Details_mac_get(swigCPtr, this);
return (cPtr == 0) ? null : new SWIGTYPE_p_unsigned_char(cPtr, false);
}
public void setSaddr(SWIGTYPE_p_sockaddr value) {
TestJNI.Details_saddr_set(swigCPtr, this, SWIGTYPE_p_sockaddr.getCPtr(value));
}
public SWIGTYPE_p_sockaddr getSaddr() {
long cPtr = TestJNI.Details_saddr_get(swigCPtr, this);
return (cPtr == 0) ? null : new SWIGTYPE_p_sockaddr(cPtr, false);
}
Proposed SWIG.i Changes:
%module Test
%rename (realId) details_t_::mac;
%typemap(javacode) struct details_t_ %{
public String getMac() {
return Test.getMacAddressAsString(this);
//this is a pointer to details_t_ struct
}
%};
%rename (Details) details_t_;
typedef struct details_t_ {
uint16_t code;
char *name;
**sockaddr *saddr;**
uint32_t saddr_len;
uint8_t flag;
ios_boolean is_child;
**unsigned char mac[6];**
} details_t;
You can do this with a javacode typemap, e.g.:
%module test
%rename (realId) Sample::id;
%typemap(javacode) struct Sample %{
public byte getId() {
return 100-getRealId(); // Transform the real call
}
public void setId(byte value) {
setRealId(value+100);
}
%};
struct Sample {
char id;
};
Renames the generated getId() and setId(), but provides a Java get/set which can be written in terms of the SWIG generated (but renamed) one. You might want to make the SWIG generated ones private though.
Related
I am migrating my code from c++17 to c++20 and need to use require instead of std::enable_if...
How to define class constructors as forward declaration with c++20 that uses require keyword on following sample ?
#include <type_traits>
class CChMyBaseClass {
};
template <
typename _ChClass,
typename _ChFunction>
class CChMyClass : public CChMyBaseClass {
private:
_ChFunction m_ChFunction;
public:
// how to do forward declaration ?
CChMyClass()
requires (std::is_member_function_pointer<_ChFunction>::value)
: CChMyBaseClass() {
}
// how to do forward declaration ?
CChMyClass()
requires (!std::is_member_function_pointer<_ChFunction>::value)
: CChMyBaseClass()
, m_ChFunction(
nullptr) {
}
};
class CChTestClass {
public:
void ChTest() {
}
};
void ChTest() {
}
int main() {
CChMyClass<CChTestClass, decltype(&CChTestClass::ChTest)> CChMyClass1();
CChMyClass<CChTestClass, decltype(&ChTest)> CChMyClass2();
return 0;
}
It's really not different from any other type of forward declaration. Just write:
template <typename _ChClass, typename _ChFunction>
class CChMyClass: public CChMyBaseClass {
...
CChMyClass() requires (std::is_member_function_pointer<_ChFunction>::value);
CChMyClass() requires (!std::is_member_function_pointer<_ChFunction>::value);
...
};
I think the difficulty is rather in the actual function definitions. But even that is not too difficult if you think about it. You just need to include the template parameters and the requires clause again:
template <typename _ChClass, typename _ChFunction>
CChMyClass<_ChClass, _ChFunction>::CChMyClass()
requires (std::is_member_function_pointer<_ChFunction>::value)
: CChMyBaseClass(), m_ChFunction(...) {
...
};
Note that in your example, you did not declare two instances of CChMyClass in main(), but rather forward declared two functions that had a CChMyClass as a return type (this is known as the most vexing parse). Just omit the () at the end, or use braces instead.
I want to use a function that requires me to pass to it as a parameter a void pointer to beginning of a block of memory. The data has to be contiguous in memory for this function to work correctly.
Right now my data is stored in a IVector<IInspectable>. Looking at the memory layout of this IVector in the debugger I see that there is 28 bytes between my data. Which I think are the 7 function pointers from IUnknown and IInspectable. How can I get the underlying contiguous memory allocation of my data?
UPDATE:
Here is the solution I came up with.
Instead of using the IVector<IInspectable> I created a custom vector using the winrt::vector_base as recommended here: https://learn.microsoft.com/en-us/windows/uwp/cpp-and-winrt-apis/collections
and I wrapped it in a windows runtime component so that I can use this custom vector from C#.
It looks like this:
MyVector.idl
namespace RuntimeComponent1
{
[default_interface]
runtimeclass MyVector
{
MyVector();
void Append(IInspectable in_val);
}
}
MyVector.h
// MyVector.h
#pragma once
#include "MyVector.g.h"
namespace winrt::RuntimeComponent1::implementation
{
using namespace winrt::Windows::Foundation;
using namespace winrt::Windows::Foundation::Collections;
struct _MyVector :
implements<_MyVector, IVector<int>, IVectorView<int>, IIterable<int>>,
winrt::vector_base<_MyVector, int>
{
auto& get_container() const noexcept
{
return m_values;
}
auto& get_container() noexcept
{
return m_values;
}
private:
std::vector<int> m_values{};
};
struct MyVector : MyVectorT<MyVector, _MyVector>
{
MyVector() = default;
void Append(Windows::Foundation::IInspectable const& in_val);
};
}
namespace winrt::RuntimeComponent1::factory_implementation
{
struct MyVector : MyVectorT<MyVector, implementation::MyVector>
{
};
}
MyVector.cpp
#include "pch.h"
#include "MyVector.h"
using namespace winrt;
namespace winrt::RuntimeComponent1::implementation
{
void MyVector::Append(Windows::Foundation::IInspectable const& in_val)
{
base_type::Append(winrt::unbox_value<int>(in_val));
}
}
Example usage:
C#
MyRuntimeComponent.MyVector my_vec = new RuntimeComponent1.MyVector();
my_vec.Append(2);
my_vec.Append(4);
MyRuntimeComponent.MyControl my_control = new RuntimeComponent0.MyControl();
my_control.do_stuff_with_contiguous_memory(my_vec);
C++
void MyControl::do_stuff_with_contiguous_memory(RuntimeComponent1::MyVector const& in_data)
{
// Yay data is contiguous
auto contiguous_data = in_data.as<MyVector>()->get_container().data();
}
The end result is that I can pass data from C# to C++/WinRT and the data will be contiguous in C++, which fixes my original problem. It works but I wonder if there might be a simpler / better way?
I would like to pass to a function a reference to a class method.
For example:
#include <functional>
struct Foo
{
int f(const int& val) const
{
return val+2;
}
};
int caller(const std::function<int(const int&)>& f)
{
return f(1);
}
int main()
{
caller([](const int& val){return val+2;}); // OK
Foo foo;
caller(foo.f); // WRONG
return 0;
}
How can I fix the second call of caller() (NB: Foo:f() is not static)?
In your case, function f doesn't use any member of Foo so it can be declared static
static int f(const int& val)
and passed as:
caller(&Foo::f);
But suppose that f cannot be declared static and you want to pass "reference" to member function of particular object.
You can use lambda in that case:
Foo foo;
caller(
[&foo](const int& val){
return foo.f(val);
}
);
foo object is captured in square brackets (in this case by reference) so that you can call f member function on that particular object.
Although it is not part of your question, I should add that it is not really useful to pass int by const reference, as you will not gain any performance improvement that way. Actually, your code will run slower than if you pass int by value.
I have a third-party C library that provides this header:
//CLibrary.h
#include <Windows.h>
#include <process.h>
typedef void (WINAPI *CLibEventCallback)(int event, void *data);
__declspec(dllexport) bool CLibStart (CLibEventCallback callback, void *data);
// CLibrary.c -- sample implementation
static CLibEventCallback cb;
void _cdecl DoWork (void *ptr)
{
for (int i = 0; i < 10; ++i)
{
cb (i*i, ptr);
Sleep (500);
}
}
__declspec(dllexport) bool CLibStart (CLibEventCallback callback, void *data)
{
cb = callback; // save address for DoWork thread...
_beginthread (DoWork, 0, data);
return true;
}
I need to create a C++/CLI class that can call CLibStart and provide a class method as the function pointer. As suggested below, this needs to be done with GetFunctionPointerForDelegate. Because the delete constructor includes 'this' and doesn't require a static method, I don't need to pass 'this' into CLibStart.
using namespace System;
using namespace System::Runtime::InteropServices;
namespace Sample {
public ref class ManagedClass
{
delegate void CLibraryDelegate (int event, void *data);
private:
CLibraryDelegate^ managedDelegate;
IntPtr unmanagedDelegatePtr;
int someInstanceData;
public:
ManagedClass()
{
this->managedDelegate = gcnew CLibraryDelegate(this, &ManagedClass::ManagedCallback);
this->unmanagedDelegatePtr = Marshal::GetFunctionPointerForDelegate(this->managedDelegate);
this->someInstanceData = 42;
}
void Start ()
{
// since the delegate includes an implicit 'this' (as static function is not needed)
// I no longer need to pass 'this' in the second parameter!
CLibStart ((CLibEventCallback) (void *) unmanagedDelegatePtr, nullptr);
}
private:
void Log (String^ msg)
{
Console::WriteLine (String::Format ("someInstanceData: {0}, message: {1}", this->someInstanceData, msg));
}
void ManagedCallback (int eventType, void *data)
{
// no longer need "data" to contain 'this'
this->Log (String::Format ("Received Event {0}", eventType));
}
};
}
All of this compiles and runs fine using this C# tester:
using System;
using Sample;
namespace Tester
{
class Program
{
static void Main(string[] args)
{
var mc = new ManagedClass();
mc.Start();
Console.ReadKey();
}
}
}
Sample output:
Received Event 0
Received Event 1
Received Event 4
Received Event 9
Received Event 16
Received Event 25
Received Event 36
Received Event 49
Received Event 64
Received Event 81
Outstanding questions:
I have this feeling that I need to use gcroot and/or pin_ptr? If
so, how? where?
Thanks.
gcroot should be in place where ref class stores delegate, like:
gcroot<CLibraryDelegate^> managedDelegate;
I have written code that allows one to traverse mapped data in the order it was entered.
The solution I coded a couple of times was:
Given a keytype, K, and and data type, D,
std::map
std::vector
When one wanted to randomly find a data entry, use map.find(K). When one wanted to traverse the map in entry order, use std::vector::iterator (begin(), end()].
This was fine, but as an exercise, I wanted to write this 'OrderedMap' as an STL compliant container. I also have (stripped down to this discussion):
template <typename K, typename D>
class OrderedMapValue
{
private:
K first_ref;
std::map<K,size_t>& m;
std::vector<D>& v;
public:
const K& first
D& second
assignment operator=(const D& data)
{
std::map<K,size_t>::const_iterator iter = m.find(first_ref);
v[iter.second] = data; // error checking of iter stripped
}
};
Further assuming
template <typename K, typename D>
class OrderedMap
{
public:
typename OrderedMapValue<K,D>& OrderedMap<K,D>::operator[](const K&);
// snip...
};
class MyClass
{
public:
MyClass(std::string s) : _my_data(s) {}
private:
std::string _my_data;
};
The following code works:
OrderedMap<std::string,MyClass*> omap;
omap["MyKey"] = new MyClass("dummy");
However, this code does not:
OrderedMap::iterator iter = omap.find("MyKey");
MyClass * obj = iter->second;
delete obj;
iter->second = new MyClass("dummy");
Assuming I have done something
a) Structurally silly or
b) Unnecessarily complex, how should this be done?
I realize that I'm likely reinventing the wheel here, but again, this effort is mainly to increase my knowledge of STL containers, their design patterns and proper use.
Thanks in advance for any insights,
I don't have a compiler right now to test this, so there could be errors, but I think you want it more like:
template <typename K, typename D>
class OrderedMap
{
private:
std::map<K,size_t> &m;
std::vector<D> &v;
public:
typename pair<K,D> TYPE;
TYPE& operator[](const K &k)
{
return v[ m[ k ]];
}
TYPE& operator[](size_t idx)
{
return v[ idx ];
}
pair<iterator,bool> insert( const TYPE& pair )
{
map<K, size_t>::const_iterator iter;
iter = m.find( pair.first );
if( iter != m.end() )
return make_pair( v[ iter.second], false );
m.insert( make_pair( pair->first, v.size() ));
v.push_back( pair->second );
return make_pair( v.last() , inserted );
}
iterator &begin()
{
return v.begin();
}
// etc
};
In OrderedMapValue::operator=, you have:
std::map<K,size_t>::const_iterator iter = m.find(first_ref);
What is first_ref? The code doesn't reference it (no pun intended) elsewhere. It looks to me like it might be a vestige from an older implementation, replaced elsewhere by the public member
const K& first.
Could this be the problem?
EDIT from the comments: The code doesn't show that first_ref is initialized anywhere; so for all I can tell, the call to m.find(first_ref) is searching for an empty string, rather than the key for the OrderedMapValue.