Why does the function with arguments have errors?

[mirro187]

error C2660 “std::packaged_task<int (int)>::operator ()”: The function does not take zero arguments

#include "thread_pool.hpp"
#include  "thread"
#include "future"
#include "functional"
#include "memory"
#include "iostream"
using namespace std;

int f(int j)
{
	return j;
}

int main(int argc, char **argv)
{
	tp::ThreadPool pool;
	//
	std::packaged_task<int(int)> t(f);
	std::future<int> r = t.get_future();
	pool.post(t);
	r.get();
	//while (1);
	getchar();
	return 0;
}

[mirro187]

What's the right thing to do?

[vittorioromeo]

Use a lambda to decide how your function is going to be invoked. E.g.

pool.post([]{ t(5); });

[mirro187]

Use a lambda to decide how your function is going to be invoked. E.g.

pool.post([]{ t(5); });

Just test pool.post([]{ t(5); }); code and there's an error occurred.

Error C3493: "t" cannot be caught implicitly because the default capture mode has not been specified

#include "thread_pool.hpp"
#include "thread"
#include "future"
#include "functional"
#include "memory"
#include "iostream"
using namespace std;

int f(int j)
{
return j;
}

int main(int argc, char **argv)
{
tp::ThreadPool pool;
//
std::packaged_task<int(int)> t(f);
std::future r = t.get_future();
pool.post([]{t(5);});
r.get();
//while (1);
getchar();
return 0;
}

[yvoinov]

You doing it wrong. Use something like that:

std::future<void> r;
std::packaged_task<int()> t([&]() { f(v_input); });
r = t.get_future();
pool.post(t);
r.wait();

PS. It tell you directly - ""t" cannot be caught implicitly because the default capture mode has not been specified". Specify capture mode in lambda.

[mirro187]

You doing it wrong. Use something like that:

std::future<void> r;
std::packaged_task<int()> t([&]() { f(v_input); });
r = t.get_future();
pool.post(t);
r.wait();

PS. It tell you directly - ""t" cannot be caught implicitly because the default capture mode has not been specified". Specify capture mode in lambda.

Thank you so much for your reply ！but, there are still some errors.
how should I modify this code?

Error C2664 "STD: : function < _Ret (void) > : : function (STD: : function < _Ret (void) > &&)" :1 cannot be parameters from the "main: : < lambda_52a96aedc09236acf9c18022602966b7 >" into "STD: : nullptr_t ConsoleApplication4" c: \ program files \ Microsoft visual studio (x86) vc 14.0 \ \ include \ the future 582

#include "thread_pool.hpp"
#include "thread"
#include "future"
#include "functional"
#include "memory"
#include "iostream"
using namespace std;

class cc{
public:
int f(int j)
{
return j;
}
};

int main(int argc, char **argv)
{
tp::ThreadPool pool;
cc obj;
std::future r;
std::packaged_task<int()> t(& {bind(&cc::f,&obj,1);});
r = t.get_future();
pool.post(t);
getchar();
return 0;
}

[yvoinov]

What would you like to achieve on so complex manner?

To post subroutine call to pool just enough to wrap it in lambda directly:

	pool.post(([=]() { f(j); }));

No future, no bind requires.

Also keep in mind: using future here lead to serialization and makes pool useless.

[mirro187]

so, there are still some errors.please use the vs2015 run this code to see your result.

**
Error C2664 "STD: : function < _Ret (void) > : : function (STD: : function < _Ret (void) > &&)" :1 cannot be parameters from the "main: : < lambda_52a96aedc09236acf9c18022602966b7 >" into "STD: : nullptr_t ConsoleApplication4" c: \ program files \ Microsoft visual studio (x86) vc 14.0 \ \ include \ the future 582
**

What would you like to achieve on so complex manner?

To post subroutine call to pool just enough to wrap it in lambda directly:

	pool.post(([=]() { f(j); }));

No future, no bind requires.

Also keep in mind: using future here lead to serialization and makes pool useless.

please,

[yvoinov]

Ah, vs2015. AFAIK this version does not fully C++11 compliant. Try to use more fresh compiler.

Unfortunately, I cant verify due to does not using Windows.

[mirro187]

Use a lambda to decide how your function is going to be invoked. E.g.

pool.post([]{ t(5); });

Thank you so much for your reply ！but, there are still some errors.
how should I modify this code?

Error C2664 "STD: : function < _Ret (void) > : : function (STD: : function < _Ret (void) > &&)" :1 cannot be parameters from the "main: : < lambda_52a96aedc09236acf9c18022602966b7 >" into "STD: : nullptr_t ConsoleApplication4" c: \ program files \ Microsoft visual studio (x86) vc 14.0 \ \ include \ the future 582

#include "thread_pool.hpp"
#include "thread"
#include "future"
#include "functional"
#include "memory"
#include "iostream"
using namespace std;

class cc{
public:
int f(int j)
{
return j;
}
};

int main(int argc, char **argv)
{
tp::ThreadPool pool;
cc obj;
std::future r;
std::packaged_task<int()> t(& {bind(&cc::f,&obj,1);});
r = t.get_future();
pool.post(t);
getchar();
return 0;
}

[yvoinov]

Your code produces syntax error:

test12.cc: In function 'int main(int, char**)':
test12.cc:21:13: error: missing template arguments before 'r'
std::future r;
^
test12.cc:22:31: error: expected primary-expression before '{' token
std::packaged_task<int()> t(& {bind(&cc::f,&obj,1);});
^
test12.cc:23:1: error: 'r' was not declared in this scope
r = t.get_future();
^
g++: error: test12.o: No such file or directory
g++: fatal error: no input files

To make it work it is enough to write:

#include "thread_pool.hpp"
#include "functional"
#include "memory"
#include "iostream"
using namespace std;

class cc{
public:
int f(int j)
{
return j;
}
};

int main(int argc, char **argv)
{
tp::ThreadPool pool;
cc obj;

pool.post([&] { obj.f(5); } );

getchar();
return 0;
}

[mirro187]

Your code produces syntax error:

test12.cc: In function 'int main(int, char**)':
test12.cc:21:13: error: missing template arguments before 'r'
std::future r;
^
test12.cc:22:31: error: expected primary-expression before '{' token
std::packaged_task<int()> t(& {bind(&cc::f,&obj,1);});
^
test12.cc:23:1: error: 'r' was not declared in this scope
r = t.get_future();
^
g++: error: test12.o: No such file or directory
g++: fatal error: no input files

To make it work it is enough to write:

#include "thread_pool.hpp"
#include "functional"
#include "memory"
#include "iostream"
using namespace std;

class cc{
public:
int f(int j)
{
return j;
}
};

int main(int argc, char **argv)
{
tp::ThreadPool pool;
cc obj;

pool.post([&] { obj.f(5); } );

getchar();
return 0;
}

Thank you so much for your reply ！but, there are still some errors.
how should I modify The following code?

#include "thread_pool.hpp"
#include "thread"
#include "future"
#include "functional"
#include "memory"

struct A {
int b(const int &p)
{
return p;
}
void c(int &i)
{
i = 43;
}
};

int main()
{
A a;
int i = 0;
tp::FixedFunction<int(const int &)> f(std::bind(&A::b, &a, i));
auto f1 = std::move(f);

tp::ThreadPool pool;

std::packaged_task<int(const int &)> t(f1);

std::future<int> r = t.get_future();

pool.post(t);
return 0;

}

[mirro187]

Thank you so much for your reply ！but, big brother... I want use std::future method to get thead result value.
so,What should I modify code?
`
#include "thread_pool.hpp"
#include "thread"
#include "future"
#include "functional"
#include "memory"

struct A {
int b(const int &p)
{
return p;
}
void c(int &i)
{
i = 43;
}
};

int main()
{
A a;
int i = 0;
//tp::FixedFunction<int(const int &)> f();
tp::ThreadPool pool;
std::packaged_task<int(const int &)> t(std::bind(&A::b, &a, i));
std::future r = t.get_future();
pool.post(t);
return 0;
}
`

Your code produces syntax error:

test12.cc: In function 'int main(int, char**)':
test12.cc:21:13: error: missing template arguments before 'r'
std::future r;
^
test12.cc:22:31: error: expected primary-expression before '{' token
std::packaged_task<int()> t(& {bind(&cc::f,&obj,1);});
^
test12.cc:23:1: error: 'r' was not declared in this scope
r = t.get_future();
^
g++: error: test12.o: No such file or directory
g++: fatal error: no input files

To make it work it is enough to write:

#include "thread_pool.hpp"
#include "functional"
#include "memory"
#include "iostream"
using namespace std;

class cc{
public:
int f(int j)
{
return j;
}
};

int main(int argc, char **argv)
{
tp::ThreadPool pool;
cc obj;

pool.post([&] { obj.f(5); } );

getchar();
return 0;
}

[yvoinov]

Using future is bad idea here, due to thread pool serialization. With this you pool will execute one task a time.

[mirro187]

Using future is bad idea here, due to thread pool serialization. With this you pool will execute one task a time.

thanks for the warning， But I still want to use std::future method... How should I pass parameters?

[yvoinov]

If you're insist....On your responsibility:

#include "thread_pool.hpp"
#include <functional>
#include <memory>
#include <iostream>
#include <future>

class cc{
public:
static int f(int j)
{
return j;
}
};

int main(int argc, char **argv)
{
tp::ThreadPool pool;
cc obj;

std::packaged_task<int()> t([&]() { return obj.f(5); });
std::future<int> r = t.get_future();
pool.post(t);
r.wait();

getchar();
return 0;
}

This works.

Don't understand, why thread pool here... It will not work as pool. Just enough to use std::async.

But I'm not C/C++ programmer.