term does not evaluate to a function taking 2 arguments--error - c++

hi I am using make_heap in my cpp program. I have written below code corresponding to it-
struct jobs {
int abs_deadline, id, rem_ET, arr_time;
};
struct compareDeadline {
bool comparator(jobs t1, jobs t2) {
return t1.abs_deadline < t2.abs_deadline;
}
};
struct compareArrTime {
bool comparator( jobs t1, jobs t2) {
return t1.arr_time < t2.arr_time;
}
};
void runningPhase(int ntasks,vector<tasks> j) {
vector<jobs> ready_queue,waiting_queue;
int system_criticality = 1, temp, timer = j[0].arr_time;
cout << "\nSCHEDULE:\n\n";
for (int i = 1; i <ntasks; i++) {
if (j[i].criticality == 1) {
temp = j[i].arr_time + j[i].deadline;
if (timer == j[i].arr_time) {
ready_queue.push_back({ temp,j[i].id, j[i].wcet[0],j[i].arr_time });
}
else {
waiting_queue.push_back({ temp,j[i].id,j[i].wcet[0],j[i].arr_time });
}
}
}
make_heap(ready_queue.begin(), ready_queue.end(), compareArrTime());
make_heap(waiting_queue.begin(), waiting_queue.end(), compareDeadline());
schedule(j, ready_queue, waiting_queue,ntasks);
}
Getting attached error
error
Any help will be apreciated.

You are passing an argument of type compareArrTime to make_heap. That's fine.
Let's call it cat. Inside make_heap, it will try to call it thus: cat(one, two).
But your compareArrTime doesn't have an operator () defined.
Hence the error.
You should write it thus:
struct compareArrTime {
bool operator ()( jobs t1, jobs t2) const {
return t1.arr_time < t2.arr_time;
}
};
and probably take t1 and t2 by const & rather than by value.

Related

invoking member functions from producer thread

Using a producer-consumer pattern I'd like to submit calls to the member functions of struct A i.e., func_1() and func_2() by passing the name of the function object (something like A::func_1), and a list of arguments taken by these functions in a queue-like buffer queue_in. I'd then like to collect these results (here a std::variant of all the possible return types (double and int)) in another buffer queue_out for later processing.
At the moment, I'm only able to hack my way by having q_in hold std::string and enumerating all the possibilities manually. Of course I'm also missing passing any possible arguments to func_1() and func_2().
#include <iostream>
#include "blockingconcurrentqueue.h" // https://github.com/cameron314/concurrentqueue
#include <variant>
using Result = std::variant<double, int>;
using queue_in = moodycamel::BlockingConcurrentQueue<std::string>;
using queue_out = moodycamel::BlockingConcurrentQueue<Result>;
struct A {
explicit A(queue_in &q_in, queue_out &q_out) {
std::thread t([&]() {
for (;;) {
std::string s;
if (q_in.wait_dequeue_timed(s, -1)) {
if (s == "1")
q_out.enqueue(this->func_1());
else if (s == "2")
q_out.enqueue(this->func_2());
}
std::this_thread::sleep_for(std::chrono::seconds(1));
}
});
t.join();
}
double func_1() const { // func_1 might have arguments!
std::cout << "func_1() called.\n";
return 13.0f;
}
int func_2() const { // func_2 might have arguments!
std::cout << "func_2() called.\n";
return 1;
}
};
void producer(queue_in &q_in, const size_t N) {
for (size_t i = 0; i != N; ++i) {
q_in.enqueue("1" /*..., arguments for func_1*/); // prefer to call the function-object instead
q_in.enqueue("2" /*..., arguments for func_2*/);
}
}
void result_consumer(queue_out &q_out) {
for (;;) {
Result r;
if (q_out.wait_dequeue_timed(r, -1)) {
std::visit([](auto &&arg) {
std::cout << "The result is: " << arg << std::endl;
}, r);
}
std::this_thread::sleep_for(std::chrono::seconds(0));
}
}
int main() {
const size_t N = 2;
queue_in q_in;
queue_out q_out;
std::thread producer_thread(producer, std::ref(q_in), N);
std::thread result_consumer_thread(result_consumer, std::ref(q_out));
A a(q_in, q_out);
producer_thread.join();
result_consumer_thread.join();
}
How can I do this instead via function objects? Second, how do I invoke any possible arguments for the member functions of A. And third, can I avoid the use of a std::variant like result type?
Taking inspiration from #n.1.8e9-where's-my-sharem. 's comments here's how I got the above to work using std::function and std::bind
using Result = std::variant<double, int>;
using FO = std::function<Result(void)>;
using queue_in = moodycamel::BlockingConcurrentQueue<FO>;
using queue_out = moodycamel::BlockingConcurrentQueue<Result>;
struct A {
explicit A(queue_in &q_in, queue_out &q_out) {
std::thread t([&]() {
for (;;) {
FO o;
if (q_in.wait_dequeue_timed(o, -1)) {
q_out.enqueue(o());
}
std::this_thread::sleep_for(std::chrono::seconds(1));
}
});
t.detach();
}
void consumer() {
}
double func_1(double x, const size_t &s) const { // note the arguments
std::cout << "func_1() called.\n";
return x + s;
}
int func_2(int x) const {
std::cout << "func_2() called.\n";
return x;
}
};
void producer(const A& a, queue_in &q_in, const size_t N) { // note the first argument: the producer() must know about some instance of A
for (size_t i = 0; i != N; ++i) {
FO o;
if (i % 2 == 0)
o = std::bind(&A::func_1, a, double(i), size_t(10));
else
o = std::bind(&A::func_2, a, int(i));
q_in.enqueue(o);
}
}
void result_consumer(queue_out &q_out) {
for (;;) {
Result r;
if (q_out.wait_dequeue_timed(r, -1)) {
std::visit([&](auto &&arg) {
std::cout << "The result is: " << arg << std::endl;
}, r);
}
std::this_thread::sleep_for(std::chrono::seconds(1));
}
}
int main() {
const size_t N = 2;
queue_in q_in;
queue_out q_out;
A a(q_in, q_out);
std::thread producer_thread(producer, std::ref(a), std::ref(q_in), N);
std::thread result_consumer_thread(result_consumer, std::ref(q_out));
producer_thread.join();
result_consumer_thread.join();
}
Output:
func_1() called.
The result is: 10
func_2() called.
The result is: 1

How to use Function Pointer as a parameter in a Class

I am trying to construct a class that is essentially a queue of futures that are all handled asynchronously and eventually all stored when main wants to get their values. I am having trouble creating the function parameters that will accept these functions and their arguments in order to create an async operation that is then pushed in to the queue of futures. The areas in question are the call constructor and the member function add(). Here is what I have so far:
#include <iostream>
#include <queue>
#include <future>
#include <thread>
using namespace std;
using longInt = unsigned long long int;
//prototypes
longInt isPrime(longInt);
template <typename return_type>
class TaskQueue {
private:
queue<future<return_type>> tasks;
public:
//return a copy of the queue
queue<future<return_type>> copy() const {
return tasks;
}
//default constructor
//does nothing, waits for input
TaskQueue() {
//do nothing
}
//call constructors
//adds task to queue
TaskQueue(return_type (*func)(), Args&& ... args) {
tasks.push(new async(func, args));
}
//copy constructor
//copies another queue to this one
TaskQueue(const queue<future<return_type>> & in) {
tasks = in.copy();
}
//setter and getter functions
//inserts a new task into the queue
void add(return_type(*func)(), Args&& ... args) {
tasks.push(new aync(in, args));
}
//returns true if the task at the top of the queue is ready
bool valid() {
return tasks.front().valid();
}
//gets the value, if the value is not ready, waits for it to be ready
//pops the top task after getting it
return_type get() {
return_type temp = tasks.top().get();
tasks.pop();
return temp;
}
//waits for the value of the top of the queue to become ready
void wait() {
tasks.top().wait();
}
};
int main() {
TaskQueue<longInt> checkPrimes;
checkPrimes.add(isPrime, 5);
longInt test = checkPrimes.get();
cout << test << endl;
}
//returns the number if it is prime or 0 if it is not
longInt isPrime(longInt n) {
if (n <= 3) {
if (n > 1) {
return n;
}
return 0;
}
if (n % 2 == 0 || n % 3 == 0) {
return 0;
}
for (unsigned short i = 5; i * i <= n; i += 6) {
if (n % i == 0 || n % (i + 2) == 0) {
return 0;
}
}
return n;
}
A compilable version:
template <typename return_type>
class TaskQueue {
private:
queue<future<return_type>> tasks;
public:
//return a copy of the queue
queue<future<return_type>> copy() const {
return tasks;
}
//default constructor
//does nothing, waits for input
TaskQueue() {
//do nothing
}
//call constructors
//adds task to queue
template <typename ... Args, typename ... Ts>
TaskQueue(return_type (*func)(Ts...), Args&& ... args) {
tasks.push(std::async(func, args...));
}
//copy constructor
//copies another queue to this one
TaskQueue(const queue<future<return_type>> & in) {
tasks = in.copy();
}
//setter and getter functions
//inserts a new task into the queue
template <typename ... Args, typename ... Ts>
void add(return_type(*func)(Ts...), Args&& ... args) {
tasks.push(std::async(func, args...));
}
//returns true if the task at the top of the queue is ready
bool valid() {
return tasks.front().valid();
}
//gets the value, if the value is not ready, waits for it to be ready
//pops the top task after getting it
return_type get() {
return_type temp = tasks.front().get();
tasks.pop();
return temp;
}
//waits for the value of the top of the queue to become ready
void wait() {
tasks.top().wait();
}
};
Demo
I think you can define a type for the function you want to pass and then apply them in the order you want. For example, the following snippet will define a intfunc type, which is a function that takes an int and returns an int.
typedef int (*intfunc) (int);
We can then define functions like
int sum2(int n) {
return n + 2;
}
int mult3(int n) {
return 3 * n;
}
and give them to a vector,
vector<intfunc> funcs;
vector<intfunc>::iterator func;
int start = 0;
funcs.push_back(sum2);
funcs.push_back(mult3);
cin >> start;
for (func = funcs.begin(); func != funcs.end(); ++func)
{
start = (*func)(start);
}
cout << start << endl;
If we enter 5 to that program, it will return 21 as expected.

Check for changes in POD variables

I'm looking for an efficient way to check if a POD variable is altered between two cycles. I've come up with this solution:
class Foo {
public:
template<typename T>
bool isChanged(T& entry);
void endCycle();
private:
std::map<void*,size_t> entryMap; // <Address orig.,Size>
std::map<void*,void*>oldVals; // <Address orig., Address cpy.>
};
template<typename T> bool Foo::isChanged(T& entry)
{
entryMap[&entry] = sizeof(T);
if(oldVals[&entry] == NULL)
return false;
if(memcmp(&entry, oldVals[&entry], entryMap[&entry]))
return true;
else
return false;
}
void Foo::endCycle()
{
// Copy all the bytes to save them for the next cycle
for( std::map<void*,size_t>::iterator entryIt = entryMap.begin();
entryIt != entryMap.end();
++entryIt)
{
if(oldVals[entryIt->first] == NULL)
oldVals[entryIt->first] = malloc(entryIt->second);
memcpy(oldVals[entryIt->first], entryIt->first, entryIt->second);
}
}
Now i can use it like this:
Foo gBar;
void aFunction()
{
int ar;
char ba[3][3];
// Some code where ar and ba are filled
if(gBar.isChanged(ar))
// Do Something
if(gBar.isChanged(ba))
// Do Something
gBar.endCycle();
}
Is this an efficient way? My goal was a method which is very easy to use inside various cyclically called functions. I cleaned all the init and free logic from the code. Any suggestions? I especially don't like the oldshool malloc, memcpy and memcmp stuff but i don't know any other way how to do it.
Edit: Found a good solution based on Red Alerts suggestions.
I think you can use templates a little more effectively here.
template <typename T>
class Foo
{
public:
static std::map<T*, T> values;
static bool isChanged(T& entry)
{
auto it = values.find(&entry);
if(it == values.end())
{
values[&entry] = entry;
}
else if(entry != it->second)
{
it->second = entry;
return true;
}
return false;
}
};
template <typename T>
std::map<T*, T> Foo<T>::values;
int main() {
int ar = 3;
cout << Foo<int>::isChanged(ar) << endl; // 0
ar = 4;
cout << Foo<int>::isChanged(ar) << endl; // 1
for(auto& value : Foo<int>::values)
cout << value.second << endl; // 4
return 0;
}
This way you get one map per type, and you don't have to worry about inadvertently messing up an alias. You do need to define operator != and have a working copy constructor for your types, but that is much better than blindly using memcmp and memcpy.
You can also make further template specializations for arrays if you need to compare those (will be a bit more code, but nothing very complicated)
Edit: To get you started, this is what your template signature should look like:
template<class T, size_t N> bool isChanged(T(&entry)[N]); //will be called for stack allocated arrays
Or you can use char* to alias all of your values. This will let you use a single map for everything (like you were doing before, but this has no memcpy/memcmp). It will only work for POD. We could manually call the destructor when overwriting the buffer, but since there is no good way to do this in the class's destructor, it's probably best to leave out heap allocated data altogether.
class Foo
{
std::map<char**, char*> values;
public:
~Foo()
{
for(auto& value : values)
{
delete[] value.second;
}
}
template<typename T> bool isChanged(T& entry)
{
char** addr = reinterpret_cast<char**>(&entry);
auto it = values.find(addr);
if(it == values.end())
{
alignas(T) char* oldBuf = new char[sizeof(T)];
T* oldEntry = new(oldBuf) T;
*oldEntry = entry;
values[addr] = oldBuf;
}
else if(entry != *(reinterpret_cast<T*>(it->second)))
{
T* oldEntry = new(it->second) T;
*oldEntry = entry;
return true;
}
return false;
}
};
After many hours i think i found a good solution. The call stays easy and there are no casts. It's a lot more complex than the C-Style version with memcopy but I think its nicer and has also the benefit that it works with complex data not just POD.
class Manager
{
public:
~Manager()
{
funcPtrs.clear();
}
void adFnc(void(*function)())
{
funcPtrs.push_back(function);
}
void runAll()
{
for(auto& val : funcPtrs)
val();
}
private:
std::vector<void (*)()> funcPtrs;
};
Manager gAllClearManager;
template<typename T>
class Data
{
public:
Data()
{
gAllClearManager.adFnc(clearValues);
}
static void clearValues()
{
values.clear();
}
static std::map<T*,std::vector<T>>& getValues() { return values; }
private:
static std::map<T*,std::vector<T>> values;
};
template <typename T>
static bool isChanged(T& entry)
{
const static Data<T>* dataP = new Data<T>();
static std::map<T*,std::vector<T>>& values = dataP->getValues();
auto it = values.find(&entry);
if(it == values.end())
{
values[&entry].push_back(entry);
}
else if(entry != it->second[0])
{
it->second[0] = entry;
return true;
}
return false;
}
template<typename T, size_t N>
bool isChanged(T (&entry)[N])
{
const static Data<T>* dataP = new Data<T>();
static std::map<T*,std::vector<T>>& values = dataP->getValues();
auto it = values.find(entry);
if( it == values.end())
{
for(int i = 0; i < N ; ++i )
values[entry].push_back(entry[i]);
return false;
}
else
{
for(int i = 0; i < N ; ++i )
{
if(it->second[i] != entry[i])
{
for(int j = 0; j < N ; ++j )
{
it->second[j] = entry[j];
}
return true;
}
}
}
return false;
}
template<typename T>
std::map<T*, std::vector<T>> Data<T>::values;
Now i can use it like:
int main() {
int ar;
std::string ba[6];
if(isChange(ar))
// Do something
if(isChange(ba))
// Do something
}
My first template is finally working! :) Thanks again Red Alert.

strange segfault using template as parameter

I have a sorted list, which takes a Comparator as parameter. In a unit test I tried to use two different comparators.
The strange thing is, using the StringReverseComparator with the two if-statements disabled (commented out), all works well and valgrind does not claim any error.
template<typename T> class Comparator {
public:
virtual int compare(const T * left, const T * right) = 0;
};
class StringReverseComparator : public Comparator<String> {
public:
int compare(const String *left, const String *right) {
int rv = strcasecmp((const char *)*left, (const char *)*right);
if (rv < 0) return 10;
if (rv > 0) return -10;
return rv;
}
};
class StringComparator : public Comparator<String> {
public:
int compare(const String *left, const String *right) {
return strcasecmp(left->operator const char*(), right->operator const char*());
}
};
As soon as I enable both if-statements, I get a segfault from sort method.
Sort method is the standard qsort by sedgewick.
const char * is an operator from String class to access the character array.
First I thought, that changing the comparator might cause troubles, so I created a new instance of sorted list. But that traps too as soon as I have the two if-statements enabled.
So what's wrong with the compare method?
//edit:
Ok, first the sort code (taken from sedgewick):
template<typename T> class SortedList {
public:
// rest omitted
protected:
void sort() { qsort(0, _size - 1); }
void qsort(int left, int right) {
if (right > left) {
const T *v = _elements[right], *tmp;
int i = left-1;
int j = right;
for (;;) {
while (_comparator->compare(_elements[++i], v) < 0) ;
while (_comparator->compare(_elements[--j], v) > 0) ;
if (i >= j) break;
tmp = _elements[i];
_elements[i] = _elements[j];
_elements[j] = tmp;
}
tmp = _elements[i];
_elements[i] = _elements[right];
_elements[right] = tmp;
qsort(left, i-1);
qsort(i+1, right);
}
}
private:
int _size;
const T **_elements;
Comparator<T> *_comparator;
};
... and here the operator char *.
by the way: String class passed all unit tests and was ok with valgrind too.
class String {
public:
// rest omitted
operator const char * () const { return _s; }
const char * operator * () const { return _s; }
private:
char *_s;
};
about usage of strcasecmp: my first attempt was:
return strcasecmp( ... ) * (-1);
using the same parameters as in StringComparator. When that failed, I tried anything I could imagine about, including the if-statements and different call syntax of operator char *.
strcasecmp does not return just -1, 0, 1 - as mentioned in many tutorials. The return value differs in size and sign and after -1, 0, 1 failed to, I tried using 10. The value has no significance, could be 815 or 42, what ever.
// edith 2
Thanks you all for your attention!
I solved it myself. The point is, the qsort algo was not safe enuf :(
The following sort code works fine (with any kind of comparator):
void qsort(int left, int right) {
if (right > left) {
const T *v = _elements[right], *tmp;
int i = left-1;
int j = right;
for (;;) {
while (++i < _size && _comparator->compare(_elements[i], v) < 0) ;
while (--j > 0 && _comparator->compare(_elements[j], v) > 0) ;
if (i >= j) break;
tmp = _elements[i];
_elements[i] = _elements[j];
_elements[j] = tmp;
}
tmp = _elements[i];
_elements[i] = _elements[right];
_elements[right] = tmp;
qsort(left, i-1);
qsort(i+1, right);
}
}
Thanks.

Unexplainable call to class constructor generates "matching function error"

When I call merge_sort I get a string of errors as such the most readable is:
no matching function call to dynamic_array<int>::dynamic_array()
Does having a base class instantiate a sub class cause that sub-class to re-instantiate the calling base class?
This was my first guess.
// Calling main function
#include "c_dynamic_array.cpp"
int main()
{
dynamic_array<int> d1(20);
d1.order();cout << d1 << endl;
d1.rorder();cout << d1 << endl;
d1.randorder();cout << d1 << endl;
d1.merge_sort();cout << d1 << endl; // This line starts a string of errors
}
// Dynamic Array Class and Merge Inner (merge sort) Class
#include "c_include.cpp"
/*
Dynamic Array
*/
using namespace std;
template <typename> class merge_inner;
template <class T> class dynamic_array
{
protected:
T* array;
public:
int size;
void rorder();
void order();
void randorder();
void print_operator(ostream&)const;
dynamic_array(int sizein)
{
size=sizein;
array=new T[size]();
}
void merge_sort()
{
merge_inner<T> M1;
}
};
template <class T> void dynamic_array<T>::print_operator(ostream &os=cout)const
{
for (int i = 0; i < size; i++) os << array[i] << endl;
}
template <class T> void dynamic_array<T>::randorder()
{
srand(time(NULL));
int *ap;
for(ap=array;ap!=array+size;++ap){*ap=rand()%size;}
}
template <class T> void dynamic_array<T>::order()
{
int *ap,i=0;
for(ap=array;ap!=array+size;++ap)
{
*ap=i;
++i;
}
}
template <class T> void dynamic_array<T>::rorder()
{
int *ap,i=size-1;
for(ap=array;ap!=array+size;++ap)
{
*ap=i;
--i;
}
}
template<class T> ostream& operator<<(ostream& stream, dynamic_array<T> const& data)
{
data.print_operator(stream);
return stream;
}
/*
Merge Sort
*/
template <class T> class merge_inner : public dynamic_array <T>
{
using dynamic_array<T>::array;
private:
const static int size;
T *scratch;
void flip_if_unordered(int &x, int &y)
{
if(array[x]>array[y])
{
int tmp=array[x];
array[x]=array[y];
array[y]=tmp;
}
}
void merge_algo(int &left, int &right_begin, int &right)
{
int iter,iter_left=left,iter_right=right_begin;
for(iter=left;iter<=right;++iter)
{
if( (iter_right>right) || ((iter_left < right_begin) && (array[iter_left]<=array[iter_right])))
{
scratch[iter]=array[iter_left];
++iter_left;
}
else
{
scratch[iter]=array[iter_right];
++iter_right;
}
}
for(iter=left;iter<=right;++iter){array[iter]=scratch[iter];}
}
void merge_recurse(int left,int right)
{
int left_end=(left+((right-left)/2));
int right_begin=left_end+1;
if(((left+1)==right)){flip_if_unordered(left,right);return;}
else if ((left==right)){return;}
else
{
merge_recurse(left,left_end);
merge_recurse(right_begin,right);
merge_algo(left,right_begin,right);
}
}
public:
merge_inner()
{
scratch = new T[size]();
if(scratch != NULL){merge_recurse(0, size);}
}
};
/*Quick Sort
void quick_sort()
{
quick_recurse(0,size);
}
void quick_recurse(int left, int right)
{
int l = left, r = right, tmp;
int pivot = array[(left + right) / 2];
while (l <= r)
{
while (array[l] < pivot)l++;
while (array[r] > pivot)r--;
if (l <= r)
{
tmp = array[l];
array[l] = array[r];
array[r] = tmp;
l++;
r--;
}
}
if (left < r)quick_recurse(left, r);
if (l < right)quick_recurse(l, right);
}
*/
dynamic_array seems to be missing a default constructor, and since it has a custom constructor the compiler will not provide one. Add this to your class:
dynamic_array()
{
size = 0;
array = new T[0](); // or NULL, but note that new T[0] will be != NULL
}
Alternatively, provide a default sizein for your existing constructor so that it can be used as a default constructor as well:
dynamic_array(int sizein = 0)
Since your base class dynamic_array<T> doesn't have a default constructor, every derived class constructor must call some base constructor one way or another. Put the base initialization in the constructor initializer list. For example:
template <typename T>
class merge_inner : public dynamic_array<T>
{
public:
merge_inner() : dynamic_array<T>(0) { }
// ...
};