I wrote a class method using STL find_if. The code is the following:
void
Simulator::CommunicateEvent (pEvent e)
{
pwEvent we (e);
std::list<pEvent> l;
for (uint32_t i = 0; i < m_simulatorObjects.size (); i++)
{
l = m_simulatorObjects[i]->ProcessEvent (we);
// no action needed if list is empty
if (l.empty ())
continue;
// sorting needed if list comprises 2+ events
if (l.size () != 1)
l.sort (Event::Compare);
std::list<pEvent>::iterator it = m_eventList.begin ();
std::list<pEvent>::iterator jt;
for (std::list<pEvent>::iterator returnedElementIt = l.begin ();
returnedElementIt != l.end ();
returnedElementIt++)
{
// loop through the array until you find an element whose time is just
// greater than the time of the element we want to insert
Simulator::m_eventTime = (*returnedElementIt)->GetTime ();
jt = find_if (it,
m_eventList.end (),
IsJustGreater);
m_eventList.insert (jt, *returnedElementIt);
it = jt;
}
}
}
Unfortunately, I later discovered that the machine that will run the code is equipped with the libstdc++ library version 4.1.1-21, which apparently is lacking find_if. Needless to say, I cannot upgrade the library, nor can I ask someone to do it.
When compiling, the error I get is:
simulator.cc: In member function ‘void sim::Simulator::CommunicateEvent(sim::pEvent)’:
simulator.cc:168: error: no matching function for call to ‘find_if(std::_List_iterator<boost::shared_ptr<sim::Event> >&, std::_List_iterator<boost::shared_ptr<sim::Event> >, sim::Simulator::<anonymous struct>&)’
simulator.cc: In static member function ‘static void sim::Simulator::InsertEvent(sim::pEvent)’:
simulator.cc:191: error: no matching function for call to ‘find_if(std::_List_iterator<boost::shared_ptr<sim::Event> >&, std::_List_iterator<boost::shared_ptr<sim::Event> >, sim::Simulator::<anonymous struct>&)’
make: *** [simulator.o] Error 1
How can I solve the problem?
I thought I could define a find_if function as described here. However, I have some concerns:
What about performance? The function that makes use of find_if needs to be as efficient as possible.
How can I do conditional compilation? I couldn't find a macro telling the version of the libstdc++ installed.
What are your thoughts about it?
TIA,
Jir
References
Source files: simulator.h and simulator.cc
Solution
Defined IsJustGreater outside the Simulator class and declared IsJustGreater_s friend of Simulator:
struct IsJustGreater_s : public std::unary_function<const pEvent, bool> {
inline bool operator() (const pEvent e1) {return (e1->GetTime () > Simulator::m_eventTime);}
} IsJustGreater;
Called IsJustGreater in find_if this way:
jt = find_if (it, m_eventList.end (), sim::IsJustGreater);
From the error, it appears that you're attempting to use an anonymous type as the argument. I do not believe anonymous types are allowed to be template arguments.
From the error, I believe you have something like this:
class Simulator {
struct {
bool operator(const pEvent& p) { ... } ;
} IsJustGreater;
}
what you want is to give it a name and then change the find_if to instantiate the class (see below)
class Simulator {
// class is now an inner named-class
struct IsJustGreater {
bool operator(const pEvent& p) { ... } ;
};
}
// This is how you use the class
jt = std::find_if(it, m_eventList.end(), IsJustGreater() );
I see that you're using the std:: qualifier before std::list but not std::find_if. Try putting the std:: in front so that the compiler can find it within the namespace.
Related
I have a struct A that inherits from other classes (which I'm not allowed to change). Inside A and it's methods I can call inherited methods (lets say A_method(int i), for example) without problem but when I tried to write a nested struct (lets say In) and call A_method(int i) and there is were I'm stuck.
The initial code looks like this, and I can't change it, is some kind of college assigment.
#include "Player.hh"
struct A : public Player {
static Player* factory () {
return new A;
}
virtual void play () {
}
};
RegisterPlayer(PLAYER_NAME);
Then I tried this:
#include "Player.hh"
struct A : public Player {
static Player* factory () {
return new A;
}
//My code
struct In {
int x;
void do_smthing() {
A_method(x);
}
}
virtual void play () {
}
};
RegisterPlayer(PLAYER_NAME);
Ok, from a beginning I knew I could't do this, for In to see it's parent class it should have a pointer to it but In is a often instantiated object in my code and I wanted to avoid passing this constantly to a constructor so I tried this aproach:
#include "Player.hh"
struct A : public Player {
static Player* factory () {
return new A;
}
//My code
static struct Aux
A* ptr;
Aux(A* _p) { ptr = _p; }
} aux;
struct In {
int x;
void do_smthing() {
aux.ptr->A_method(x);
}
}
virtual void play () {
//the idea is to call do_smthing() here.
}
};
RegisterPlayer(PLAYER_NAME);
What I want to avoid (if possible) is something like this:
struct In {
int x;
A* ptr;
In (A* _p) : ptr(_p) {}
void do_smthing() {
ptr->A_method(x);
}
}
The main reason for this: I have more struct definitions and they they are instantiated multiple times through the rest of the (omitted) code, and I don't like the idea of seeing In(this) so many times.
I don't know if I'm completly missing something or what I want to do it's just not possible... Please ask for clarifications if necessary.
(Also, performance is kind of critical, my code will be tested with limited CPU time so I kinda have to avoid expensive approachs if possible. Using C++11)
There is no way you can skip passing the this pointer. Instead, you could create a helper function in A:
template <typename InnerType, typename ...Params>
InnerType makeInner(Params&&... params)
{
return InnerType(this, std::forward<Params>(params)...);
}
Then you can use
auto * a = A::factory();
auto inner = a->makeInner<A::In>();
I have some suggestions which are not directly related to you question but may help:
A::facotry() returns a std::unique_ptr<A> instead of raw pointer
Try to describe what problem you are trying to solve. I have a strong feeling that there can be a better design other than creating many nested structs.
I don't see passing a this pointer could have any impact on the performance. The more important thing is to identify the path that is latency-sensitive and move expensive operations out of those paths.
I am facing problem while running gtest for the following code sample.
ignore header includes as its compilable and running fine.
Error:
GMOCK WARNING:
Uninteresting mock function call - returning default value.
Function call: receive(0x7ffcee4fc990, 0x7ffcee4fc900)
Returns: 0
NOTE: You can safely ignore the above warning unless this call should not happen. Do not suppress it by blindly adding an EXPECT_CALL() if you don't mean to enforce the call. See https://github.com/google/googletest/blob/master/googlemock/docs/CookBook.md#knowing-when-to-expect for details.
/data/home/sipadhy/unit_test_research/gTest/ImplClassTest.cpp:174: Failure
Actual function call count doesn't match EXPECT_CALL(mockImplClass, receive(_, _))...
Expected: to be called at least once
Actual: never called - unsatisfied and active
Sample Code:
// Main Class where function to be mocked
class ImplClass
{
public:
virtual int receive(structX* x, structY* y){ // some logic }
};
// An intermidiate class which calls the main class
class IntermidiateClass
{
std::shared_ptr<ImplClass> implClassPtr = nullptr;
public:
setImplClassptr(std::shared_ptr<ImplClass> ptr)
{
implClassPtr = ptr;
}
int getValue()
{
structX x;
structY y;
return(implClassPtr->receive(x, y));
}
};
// Mock Class
class MockImplClass: public ImplClass
{
public:
MOCK_METHOD2(receive, int(structX, structY));
}
// Test case
TEST(MyTest, TEST1)
{
MockImplClass mockImplClass;
IntermidiateClass intermidiateObj;
intermidiateObj.setImplClassptr(std::make_shared<MockImplClass>());
EXPECT_CALL(mockImplClass, receive(_, _))
.Times(AtLeast(1))
.WillRepeatedly(Return(1));
int retVal = intermidiateObj.getValue();
}
Thanks,
Siva
You create a brand new object of the MockImplClass class here:
std::make_shared<MockImplClass>()
Thus your first created object
MockImplClass mockImplClass;
never gets used to call receive()
There is a custom defined map, with an element std::function()>.
The lambda code is working, but I don't know how to expand it to a normal formation. The code is following.
class TestA{
public:
TestA() {}
~TestA() {}
TestA(const TestA &) {}
static void print()
{
cout << __FUNCTION__ << endl;
return;
}
};
void testComplexMap1()
{
typedef map<string, std::function<std::unique_ptr<TestA>()>> TempMap;
TempMap m;
// the lambda format code, it works
//m.insert({ "TestA", []() {return std::unique_ptr<TestA>(new TestA());}});
// I want to expand it, but failed.
TestA *t = new TestA();
//function<unique_ptr<TestA>()> fp(unique_ptr<TestA>(t));
function<unique_ptr<TestA>()> fp(unique_ptr<TestA>(t)()); //warning here
//m.emplace("TestA", fp); // compile error here
}
Any help will be greatly appreciated.
fp is not initialized with a function so compilation fails.
You can expand it like this:
TestA *t = new TestA();
std::unique_ptr<TestA> UT(t);
auto func = [&]() { return move(UT);};
std::function<std::unique_ptr<TestA>()> fp(func);
m.emplace("TestA", fp);
See DEMO.
In C++ everything that looks like it could be a declaration is treated as such.
This means the line
function<unique_ptr<TestA>()> fp(unique_ptr<TestA>(t)());
is interpreted as:
fp is the declaration of a function returning an std::function<unique_ptr<TestA>()> and expecting a parameter called t which is a function pointer to a function returning a std::unique_ptr<TestA> and getting no parameter. (Which is not what you intended.)
This also means that the t in this line is not the same t as in the previous line.
You have to pass fp something that is actually callable like this:
std::unique_ptr<TestA> f() {
return std::make_unique<TestA>();
}
void testComplexMap1() {
// ...
function<unique_ptr<TestA>()> fp(f);
m.emplace("TestA1", fp);
}
If you want to add a function to the map that wraps an existing pointer into a unique_ptr you would need either a functor:
class Functor {
public:
Functor(TestA * a) : m_a(a) {}
~Functor() { delete m_a; }
std::unique_ptr<TestA> operator()(){
auto x = std::unique_ptr<TestA>(m_a);
m_a = nullptr;
return std::move(x);
}
private:
TestA * m_a;
};
void testComplexMap1() {
//...
TestA * t = new TestA();
m.emplace("TestA", Functor(t));
}
Or a lambda with capture:
void testComplexMap1() {
//...
TestA * t = new TestA();
m.emplace("TestA", [t](){ return std::unique_ptr<TestA>(t); });
}
The lamda is translated more or less to something like the Functor class. However in each case you have to be really careful: The functions in the map that encapsulate an existing pointer into a std::unique_ptr can and should only be called once.
If you don't call them, memory allocated for t won't be freed. If you call them more than once you get either a std::unique_ptr to nullptr (in my Functor class variant) or a more than one std::unique_ptr tries to manage the same memory region (in the lambda with capture variant), which will crash as soon as the second std::unique_ptr is deleted.
In short: I would advice against writing code like this and only put functions in the map that are callable multiple times.
I'm writing a simple, lightweight engine in D. For the input calls I use GLFW3. The library in question uses callbacks to send input events to the program.
What I would like is to use a method from a class as the callback function, rather than a function. This is proving difficult (just as it is in C++). I believe there is an elegant way to do it, but this is how I got it right now.
public void initialise(string logPath) {
[...]
m_Window = new RenderWindow();
m_Window.create();
// Lets set up the input loop.
GLFWkeyfun keyCB = function(GLFWwindow* win, int key, int scancode, int action, int mods) {
printf("Got key event: %d:%d:%d:%d\n");
RenderWindow rw = Root().getRenderWindow();
switch (key) {
case KeyboardKeyID.Q:
glfwSetWindowShouldClose(win, true);
break;
case KeyboardKeyID.H:
if (rw.hidden) {
rw.show();
} else {
rw.hide();
}
break;
default:
break;
}
};
glfwSetKeyCallback(m_Window.window, keyCB);
}
Here is the definition of the callback setting function and type:
extern (C) {
alias GLFWkeyfun = void function(GLFWwindow*, int, int, int, int);
GLFWkeyfun glfwSetKeyCallback(GLFWwindow*, GLFWkeyfun);
}
What I would like to do instead, is create a method that is part of the class. Is there any way to do this?
A solution I tried was a static method wrapped around in extern (C), this worked for calling it, but then I could (obviously) not access this or any other methods, which defeats the point of the exercise.
Thanks in advance.
The way I'd do it is to have a static map of the pointers to the class, so like:
static YourWindowClass[GLFWwindow*] mappings;
Then, in the constructor, once you get a GLFWwindow pointer, add it right in:
mappings[m_Window.window] = this;
Now, make the static extern(C) function to use as the callback. When it gets a pointer from C, look up your class reference in that mappings array and then go ahead and call the member function through that, forwarding the arguments.
So a bit of an extra step, but since it doesn't look like the callback lets you pass user-defined data to it (BTW, attention all lib writers: user-defined void* to the callbacks is sooooo useful, you should do it whenever possible!), but since it doesn't do that the associative array is the next best thing.
Well, I have figured it out my own. The solution I went with was a Singleton class InputManager. Instances of RenderWindow attach themselves to it with the following function. The InputManager then creates an anonymous function() for the RenderWindow that receives events, which then calls a function that handles the actual event.
The idea is then that listeners attach themselves to the InputManager and receive keyboard events for the RenderWindow they requested.
class InputManager {
private static InputManager m_Instance;
private RenderWindow[] m_Watched;
private KeyboardListener[][RenderWindow] m_KeyListeners;
public void recvKeyEvent(GLFWwindow* w, int k, int c, int a, int m) {
writeln("Received key: ", k);
}
public void watch(RenderWindow win) {
if (!isWatched(win)) {
// Relay the key callbacks onto the InputManager.
GLFWkeyfun keyCB = function(GLFWwindow* w, int k, int c, int a, int m) {
InputManager().recvKeyEvent(w, k, c, a, m);
};
glfwSetKeyCallback(win.window, keyCB);
}
}
private bool isWatched(RenderWindow win) {
foreach(RenderWindow w; m_Watched) {
if (win == w) {
return true;
}
}
return false;
}
public static InputManager opCall() {
if (m_Instance is null) {
m_Instance = new InputManager();
}
return m_Instance;
}
private this() {
// nothing
}
}
Works like a charm, now to figure out how to properly attach listeners elegantly.
For those curious, the full source code with how this is set up can be found at https://github.com/Adel92/Mage2D. I hope it helps someone else in a similar position with callbacks.
Is there a way to implement an extension method to a generic type that takes in arguments a Func of another type?
For exemple, a usage something similar to this:
myFirstObject.Extension<myOtherObject>( other => other.Prop );
Or with a more complicated Func:
myFirstObject.Extension<myOtherObject>( other => other.Prop > 2 && other.Prop < 15 );
I found some related question like this one, but in my case, I need generic types inside the extension method too.
Here's what I came up with:
public static bool Extension<TSource, TIn, TKey>(this TSource p_Value, Expression<Func<TIn, TKey>> p_OutExpression)
{ return true; }
However, when I try to use it, it does not take into consideration the second type.
Am I missing something?
Look at this:
s => s.Length;
How's the compiler suppose to know whether or not s is a string or s is an array or some other type that has a Length property? It can't, unless you give it some information:
(string s) => s.Length;
Oh, there we go. So now, try this:
myFirstObject.Extension((myOtherObject o) => o.Prop > 2 && o.Prop < 15);
That will work, because you've told the compiler what it should use for TIn, and it can figure out what to use for TKey based on the expression.
I found that another solution would be to create another method that takes in argument a type.
For instance:
Void Extension(Type p_Type, [THE TYPE] p_Params)
{
MethodInfo realExtensionMethod = typeof([CLASS CONTAINING THE METHOD]).GetMethod("RealExtension");
realExtensionMethod = realExtensionMethod.MakeGenericMethod(p_Type);
realExtensionMethod.Invoke(null, new object[] {p_Type, p_Params });
}
Void RealExtension<TYPE>(params)
{
}
Then at usage time:
Type objectType = typeof(myOtherObject);
myFirstObject.Extension(objectType, other => other.Prop );
When you call a generic method in C# you can explicitly declare all of the generic type parameters or you can have them all inferred, but you cannot have some explicitly declared and some inferred.
So, if I had this method:
public void Foo<X, Y>(X x, Y y)
{
/* Do somethhing */
}
Then here's what works and what doesn't:
int a = 42;
string b = "Hello, World!";
// Legal
Foo(a, b);
Foo<int, string>(a, b);
//Illegal
Foo<int>(a, b);
The best you can do is move the first generic parameter up to the class level, but not it won't work as an extension method. Nevertheless you may like this approach.
public static class Class<TSource>
{
public static bool Method<TIn, TKey>(
TSource p_Value,
Expression<Func<TIn, TKey>> p_OutExpression)
{
return true;
}
}
Now you can call it like this:
Expression<Func<long, decimal>> f =
l => (decimal)l;
var result = Class<int>.Method(a, f);
But as I say, it won't work as an extension method now.