schedule an event with std::cout as an argument to callback function failed

JTL

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Aug 24, 2016, 8:06:29 PM8/24/16

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Hi,

I modified mesh.cc to try to pass std::cout to the scheduler as the argument to the call back function. The code failed to compile with the error messages:

[1909/2606] Compiling src/mesh/examples/mesh.cc

../src/mesh/examples/mesh.cc: In member function ‘int MeshTest::Run()’:

../src/mesh/examples/mesh.cc:228:74: error: lvalue required as unary ‘&’ operand

Simulator::Schedule (Seconds (m_totalTime), &MeshTest::Report(std::cout), this);

^

../src/mesh/examples/mesh.cc: In member function ‘void MeshTest::Report(std::ostream&)’:

../src/mesh/examples/mesh.cc:242:84: error: ‘std::ostream’ has no member named ‘str’

std::cerr << "Printing mesh point device #" << n << " diagnostics to " << os.str () << "\n";

^

../src/mesh/examples/mesh.cc:244:19: error: ‘std::ostream’ has no member named ‘str’

of.open (os.str ().c_str ());

^

../src/mesh/examples/mesh.cc:247:56: error: ‘std::ostream’ has no member named ‘str’

std::cerr << "Error: Can't open file " << os.str () << "\n";

The following changes are made to mesh.cc:

line 102: void Report (std::ostream & os);

line 228: Simulator::Schedule (Seconds (m_totalTime), &MeshTest::Report(std::cout), this);

line 235: MeshTest::Report (std::ostream &os)

comment out line 240

as oppose to the original lines:

line 102: void Report();

line 228: Simulator::Schedule (Seconds(m_totalTime), &MeshTest::Report(), this);

line 235: MeshTest::Report()

The original mesh.cc can be access here: https://www.nsnam.org/doxygen-release/mesh_8cc_source.html

Please let me know what I have done wrong and/or how to pass std::cout as an argument to the callback function for Scheduler. Thanks

JTL

Konstantinos

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Aug 25, 2016, 3:55:53 AM8/25/16

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Hi,

Peter was probably confused and posted the solution to another thread.. (https://groups.google.com/d/msg/ns-3-users/4t2vwE3ldIg/z5vv1S8QBgAJ)

I can help weigh the first error. It should be
Simulator::Schedule (Seconds (m_totalTime), &MeshTest::Report, this, std::cout);
However, the second error will still occur. Are you sure &MeshTest::Report() can write directly to std::cout? Check the usage in the examples.
Peter

pdbarnes

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Aug 25, 2016, 9:41:10 AM8/25/16

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Whoops! Don't offer to help late at night!

JTL

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Aug 25, 2016, 12:48:14 PM8/25/16

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Hi, Peter,

Thank you very much for your help. You are right about the MeshTest::Report() is not able to handle the std::cout. I had to comment out most of the function body to avoid errors when compile.

I changed the code according to your suggestion but it seems that the compiler invokes the wrong template: Schedule(const ns3::Time&, MEM, OBJ, T1) instead of Schedule(const ns3::Time&, void(*)(U1), OBJ, T1) or something similar to this. On top of that, the copy constructor is called when passing std::cout as the 4th argument. and the following error message popped up. Could you help take a look into the problem? I have attached my version of the mesh.cc for your reference.

Here are the error messages:

In file included from /usr/include/c++/4.8/ios:42:0,

from /usr/include/c++/4.8/ostream:38,

from /usr/include/c++/4.8/iostream:39,

from ./ns3/fatal-error.h:24,

from ./ns3/abort.h:24,

from ./ns3/core-module.h:10,

from ../src/mesh/examples/mesh.cc:47:

/usr/include/c++/4.8/bits/ios_base.h: In copy constructor ‘std::basic_ios<char>::basic_ios(const std::basic_ios<char>&)’:

/usr/include/c++/4.8/bits/ios_base.h:792:5: error: ‘std::ios_base::ios_base(const std::ios_base&)’ is private

ios_base(const ios_base&);

^

In file included from /usr/include/c++/4.8/ios:44:0,

from /usr/include/c++/4.8/ostream:38,

from /usr/include/c++/4.8/iostream:39,

from ./ns3/fatal-error.h:24,

from ./ns3/abort.h:24,

from ./ns3/core-module.h:10,

from ../src/mesh/examples/mesh.cc:47:

/usr/include/c++/4.8/bits/basic_ios.h:66:11: error: within this context

class basic_ios : public ios_base

^

In file included from /usr/include/c++/4.8/iostream:39:0,

from ./ns3/fatal-error.h:24,

from ./ns3/abort.h:24,

from ./ns3/core-module.h:10,

from ../src/mesh/examples/mesh.cc:47:

/usr/include/c++/4.8/ostream: In copy constructor ‘std::basic_ostream<char>::basic_ostream(const std::basic_ostream<char>&)’:

/usr/include/c++/4.8/ostream:58:11: note: synthesized method ‘std::basic_ios<char>::basic_ios(const std::basic_ios<char>&)’ first required here

class basic_ostream : virtual public basic_ios<_CharT, _Traits>

^

../src/mesh/examples/mesh.cc: In member function ‘int MeshTest::Run()’:

../src/mesh/examples/mesh.cc:228:81: note: synthesized method ‘std::basic_ostream<char>::basic_ostream(const std::basic_ostream<char>&)’ first required here

Simulator::Schedule (Seconds (m_totalTime), &MeshTest::Report, this, std::cout);

^

In file included from ./ns3/event-garbage-collector.h:25:0,

from ./ns3/core-module.h:29,

from ../src/mesh/examples/mesh.cc:47:

./ns3/simulator.h:1224:9: error: initializing argument 4 of ‘static ns3::EventId ns3::Simulator::Schedule(const ns3::Time&, MEM, OBJ, T1) [with MEM = void (MeshTest::*)(std::basic_ostream<char>&); OBJ = MeshTest*; T1 = std::basic_ostream<char>]’

EventId Simulator::Schedule (Time const &delay, MEM mem_ptr, OBJ obj, T1 a1)

Thank you very much!

JT

mesh.cc

pdbarnes

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Aug 26, 2016, 4:33:17 PM8/26/16

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The error message has the hint you need:

error: initializing argument 4 of

static ns3::EventId ns3::Simulator::Schedule(const ns3::Time&, MEM, OBJ, T1)

[with MEM = void (MeshTest::*)(std::basic_ostream<char>&); OBJ = MeshTest*; T1 = std::basic_ostream<char>]

The argument to the MeshTest::Report should be a reference "&":

Simulator::Schedule (Seconds (m_totalTime), &MeshTest::Report, this, &std::cout);

HTH,

Peter

JTL

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Aug 28, 2016, 3:37:26 PM8/28/16

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Hi Peter,

Thank you very much for your feedback. I did what you suggested and the error message below popped up

In file included from ./ns3/simulator.h:26:0,

from ./ns3/event-garbage-collector.h:25,

from ./ns3/core-module.h:29,

from ../src/mesh/examples/mesh.cc:47:

./ns3/make-event.h: In instantiation of ‘void ns3::MakeEvent(MEM, OBJ, T1)::EventMemberImpl1::Notify() [with MEM = void (MeshTest::*)(std::basic_ostream<char>&); OBJ = MeshTest*; T1 = std::basic_ostream<char>*]’:

./ns3/make-event.h:358:3: required from ‘ns3::EventImpl* ns3::MakeEvent(MEM, OBJ, T1) [with MEM = void (MeshTest::*)(std::basic_ostream<char>&); OBJ = MeshTest*; T1 = std::basic_ostream<char>*]’

./ns3/simulator.h:1226:56: required from ‘static ns3::EventId ns3::Simulator::Schedule(const ns3::Time&, MEM, OBJ, T1) [with MEM = void (MeshTest::*)(std::basic_ostream<char>&); OBJ = MeshTest*; T1 = std::basic_ostream<char>*]’

../src/mesh/examples/mesh.cc:228:82: required from here

./ns3/make-event.h:353:7: error: invalid initialization of reference of type ‘std::basic_ostream<char>&’ from expression of type ‘TypeTraits<std::basic_ostream<char>*>::ReferencedType {aka std::basic_ostream<char>*}’

(EventMemberImplObjTraits<OBJ>::GetReference (m_obj).*m_function)(m_a1);

^

&std::cout seems to be treated as pointer by the compiler. This is puzzling to me as this simple C++ code snippet works just fine:

#include <iostream>

using namespace std;

class myClass{

public:

void myPrint(ostream& os)

{

os<<"test";

};

int main() {

myClass r;

r.myPrint(cout);

return 0;

}

Don't know how to intepret this.... any feedback is highly appreciated. Thank you very much.

JT

Craig Dowell

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Aug 30, 2016, 1:28:22 AM8/30/16

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Look for OutputStreamWrapper in the documentation.

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JTL

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Aug 30, 2016, 3:51:53 PM8/30/16

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Hi Craig,

It works perfectly with OutputStreamWrapper. Thanks

JT

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