I am making program in which i try to make boost packaged_task then take its future in vector and launch it with asio post.
when i try to make packaged_task ,it gives me this error:
Error C2440 'return': cannot convert from 'void (__cdecl &)(boost::asio::yield_context)' to 'void (&)(boost::asio::yield_context)'
this is the relevant code:
typedef boost::packaged_task<std::string(boost::asio::yield_context)> task_t;
boost::shared_ptr<task_t> task = boost::make_shared<task_t>(boost::bind(&HTTPRequest::Execute, mClientRequestsVariables[m_HttpClient_request_name]->shared_from_this() , boost::placeholders::_1, m_HttpClient_request_name, Get_mHTTPClient_Responses_Map_shared_pointer()));
boost::future<std::string> fut = (task->get_future());
mPendingData.push_back(std::move(fut)); // C++11 possible: (std::move(fut) when fut is a unique_future);
mIos.post(boost::bind(&task_t::operator(), task));
and this is the definition of HTTPRequst::Execute :
HTTPRequest::HTTPRequest(boost::asio::io_service& ios, unsigned int id, std::string URL, const HTTPServiceResolve& resolve_addr, boost::shared_ptr<LoggingClass_2> mHTTPRequest_LoggingInstance_shared_pointer)
and the class HTTPRequest is derived from enable_shared_from_this .
the error is in bind.hpp so i find in vs output windows clues to the included part of code.
why is this error happening?and what is the solution??
Related
I'm trying to open a file using a string parameter, however I'm getting the following error:
error C2664: 'void std::basic_ifstream<_Elem,_Traits>::open(const wchar_t *,std::ios_base::openmode,int)' : cannot convert parameter 1 from 'System::String ^' to 'const wchar_t *'
How do you convert System::String ^ to const wchar_t *?
As Hans points out, simple conversion is necessary. It would look similar to the following:
System::String ^str = L"Blah Blah";
pin_ptr<const wchar_t> convertedValue = PtrToStringChars(str); // <-- #include <vcclr.h>
const wchar_t *constValue = convertedValue; // <-- Unnecessary, but to be completely verbose
void std::basic_ifstream<_Elem, _Traits>::open(constValue, mode, i);
I have been trying to figure this out for a few days now and cannot figure it out. I am using CCS as the IDE and I am working on windows. I am trying to create an RTOS Kernel on a MSP432 and need to use pthreads. I have been able to use pthreads in other examples but I am trying to do my own program and I get this issue when building :
unresolved symbol pthread_create, first referenced in ./armrtk/src/task.obj
I have included the file path into CCS and I cannot use a .cfg file because I am not using XDCTools. I just need help with this and I greatly appreciate it.
I also get a warning:
in pthread_create in TASK.C: #169-D argument of type "void *" is incompatible with parameter of type "void *(*)(void *)"
TASK.H
#ifndef TASK_H
#define TASK_H
#include <pthread.h>
struct task_t {
pthread_t* thread;
int threadCheck;
int state;
};
void *task1(void);
void *task2(void);
struct task_t *create_task(void* functionptr);
void delete_task(void *task);
#endif
TASK.C
#include <task.h>
#include <stdlib.h>
#include <pthread.h>
#define BLOCKED -1
#define READY 0
#define RUNNING 1
int testValue1 = 0;
int testValue2 = 0;
struct task_t *new_task;
pthread_t pntr;
struct task_t *create_task(void* functionptr) {
new_task = malloc(sizeof(struct task_t));
if(!new_task)
return NULL;
//set State of the new thread to ready
new_task->state = 0;
// check to see if pthread is created
**new_task->threadCheck = pthread_create(new_task->thread, NULL, functionptr, NULL);**
if(new_task->threadCheck!= 0){
//thread failed
return NULL;
}
return new_task;
}
void delete_task(void *task) {
if(task != NULL){
free(task);
pthread_exit(NULL);
}
}
The unresolved symbol error is a linker error, not a compiler error. You have failed to link the pthreads library.
With respect to the warning functionptr is a void* where pthread_create() expects a pointer-to-function with signature void fn(void*).
Your task functions have a different signature in any case: void fn(void), so in any event you will need to cast the function pointer in the call to pthread_create() (although you are loosing a useful means of passing information into a task function by omiting the void* argument).
Modify task.h:
typedef void* (*task_t)(void);
struct task_t *create_task( task_t functionptr);
The in task.cpp
new_task->threadCheck = pthread_create( new_task->thread,
NULL,
(void (*)(void *))functionptr,
NULL ) ;
The cast in the pthread_create() call alone would supress the warning, but it bad form to pass a function pointer as a generic void* since it would prevent the compiler warning you if you were to pass anything other then a function pointer of the expected form to to the create_task()`
I have a fortran subroutine, FortranShake, and a C++ main function, HandShakingTest.cpp.
I'm trying to call a fortran subroutine from CLR C++.
I'm getting two batches of errors. Let's call them ERROR(1) and ERROR(2). I'd really appreciate if you could help me understand why these errors are happening.
When I try to compile with the following:
cl /clr HandShakingTest.cpp
I get the following ERROR(1):
HandShakingTest.obj : error LNK2028: unresolved token (0A00030A) "extern "C" void __c
ecl FortranShake(int &)" (?FortranShake##$$J0YAXAAH#Z) referenced in function "int __
lrcall main(cli::array<class System::String ^ >^)" (?main##$$HYMHP$01AP$AAVString#Sys
em###Z)
HandShakingTest.obj : error LNK2019: unresolved external symbol "extern "C" void __cd
cl FortranShake(int &)" (?FortranShake##$$J0YAXAAH#Z) referenced in function "int __c
rcall main(cli::array<class System::String ^ >^)" (?main##$$HYMHP$01AP$AAVString#Syst
m###Z)
HandShakingTest.exe : fatal error LNK1120: 2 unresolved externals
I then used the following commands to compile instead:
ifort /c FortranShake.f //Which compiles fine
cl /c /clr HandShakingTest.cpp //compiles fine
cl /o test HandShakingTest.obj FortranShake.obj //ERROR(2) occurs
ERROR(2) consists of:
MSVCRT.lib(ti_inst.obj) : error LNK2005: "private: __thiscall type_info::type_info(cla
ss type_info const &)" (??0type_info##AAE#ABV0##Z) already defined in LIBCMT.lib(typin
fo.obj)
MSVCRT.lib(ti_inst.obj) : error LNK2005: "private: class type_info & __thiscall type_i
nfo::operator=(class type_info const &)" (??4type_info##AAEAAV0#ABV0##Z) already defin
ed in LIBCMT.lib(typinfo.obj)
MSVCRT.lib(merr.obj) : error LNK2005: __matherr already defined in LIBCMT.lib(_matherr
_.obj)
LINK : warning LNK4098: defaultlib 'MSVCRT' conflicts with use of other libs; use /NOD
EFAULTLIB:library
HandShakingTest.obj : error LNK2028: unresolved token (0A00030A) "extern "C" void __cd
ecl FortranShake(int &)" (?FortranShake##$$J0YAXAAH#Z) referenced in function "int __c
lrcall main(cli::array<class System::String ^ >^)" (?main##$$HYMHP$01AP$AAVString#Syst
em###Z)
HandShakingTest.obj : error LNK2019: unresolved external symbol "extern "C" void __cde
cl FortranShake(int &)" (?FortranShake##$$J0YAXAAH#Z) referenced in function "int __cl
rcall main(cli::array<class System::String ^ >^)" (?main##$$HYMHP$01AP$AAVString#Syste
m###Z)
libifcoremt.lib(for_main.obj) : error LNK2019: unresolved external symbol _MAIN__ refe
renced in function _main
test.exe : fatal error LNK1120: 3 unresolved externals
Here's the HandShakingTest.cpp:
#include "stdio.h"
#include <stdlib.h>
#include <Windows.h>
#using <System.DLL>
#using <System.Windows.Forms.DLL>
using namespace std;
using namespace System;
using namespace System::IO;
using namespace System::Diagnostics;
using namespace System::ComponentModel;
using namespace System::Collections;
using namespace System::Windows::Forms;
extern "C" {void FortranShake(int&);}
int main(array<System::String ^> ^args)
{
Process^ testHand = gcnew Process();
testHand->StartInfo->UseShellExecute = false;
testHand->StartInfo->RedirectStandardInput = true;
testHand->StartInfo->RedirectStandardOutput = true;
testHand->StartInfo->ErrorDialog = true;
int numDebug = 0;
String^ returnedDebug = "Nothing";
FortranShake(numDebug);
StreamReader^ FromHandProcess = testHand->StandardOutput;
StreamWriter^ ToHandProcess = testHand->StandardInput;
String^ Line;
Line = FromHandProcess ->ReadLine();
if (Line->Equals("Enter Hand") )
{
Console::WriteLine(L"Hand Started!");
}
ToHandProcess ->WriteLine(numDebug.ToString());
returnedDebug = FromHandProcess ->ReadLine();
MessageBox::Show(returnedDebug);
return 0;
}
Here is the Fortran Subroutine:
SUBROUTINE FortranShake(GP_DEBUG)
IMPLICIT DOUBLE PRECISION (A-H,O-Z)
INN = 5
WRITE(06,'(a)') 'Enter Hand'
READ(INN,*) GP_DEBUG
GP_DEBUG = GP_DEBUG + 55
WRITE(06,*) GP_DEBUG
RETURN
END
Your first error is actually a linker error - without the /c command line switch you are compiling and linking in one step. No Fortran code or object code has been provided.
Your second error is because:
You have specified (through omission) mismatching runtime libraries for the C++ and the Fortran. You need to decide whether you want to use static linking (the default for the current (as of today, but not necessarily as of next month...) release of Intel Fortran on windows) or dynamic linking (the default for the MS C++ compiler). Perhaps add /MD to the ifort command line, which specifies dynamic linking.
Without compiler options or directives to the contrary, the equivalent identifier for the Fortran procedure in C code as generated by that Fortran compiler is an upper case variant of the Fortran procedure's name - i.e. in the C++ code call the procedure FORTRANSHAKE. If you can write your Fortran code to the F2003 standard, you should use the C interoperability features of that language (BIND(C,...)) to control the C binding name of the Fortran procedure and ensure calling conventions, etc align.
The dummy argument of the Fortran subroutine has the DOUBLE PRECISION type specifier, which is equivalent to double in the C++ for this combination of compilers, not int. Again, F2003 introduces features that can make this alignment of argument types more robust.
I am using wxWidgets 2.9.4 in Visual Studio 2012 and I keep getting these two error messages:
Error 1 error C2664: 'MessageBoxW' : cannot convert parameter 2 from 'const char *' to 'LPCWSTR'
IntelliSense: argument of type "const char *" is incompatible with parameter of type "LPCWSTR"
My code is:
#ifdef _WIN32
std::string msg;
StringFromFormatV(&msg, format, args);
retval = IDYES == MessageBox(0, msg.c_str(), "ERROR! Continue?", MB_ICONQUESTION | MB_YESNO);
You are compiling your project using multi-byte characters as default. You can change that in your project's properties, or you can use msg.wc_str(), or even enforce the use of MessageBoxA instead of using the macro MessageBox.
I was trying out lambda functions and making a jump table to execute them, but I found g++ didn't recognize the type of the lambda function such that I could assign them to an array or tuple container.
One such attempt was this:
auto x = [](){};
decltype(x) fn = [](){};
decltype(x) jmpTable[] = { [](){}, [](){} };
On compilation I get these errors:
tst.cpp:53:27: error: conversion from ‘main()::<lambda()>’ to non-scalar type ‘main()::<lambda()>’ requested
tst.cpp:54:39: error: conversion from ‘main()::<lambda()>’ to non-scalar type ‘main()::<lambda()>’ requested
Hmmmm, can't convert from type A to non-scalar type A? What's that mean? o.O
I can use std::function to get this to work, but a problem with that is it doesn't seem to work with tuple:
function<void()> jmpTable[] = [](){}; // works
struct { int i; function<void()>> fn; } myTuple = {1, [](){}}; // works
tuple<int, function<void()>> stdTuple1 = {1, [](){}}; // fails
tuple<int, function<void()>> stdTuple2 = make_tuple(1, [](){}); // works
tst.cpp:43:58: error: converting to ‘std::tuple<int, std::function<void()> >’ from initializer list would use explicit constructor ‘std::tuple<_T1, _T2>::tuple(_U1&&, _U2&&) [with _U1 = int, _U2 = main()::<lambda()>, _T1 = int, _T2 = std::function<void()>]’
Constructor marked explicit? Why?
So my question is if I am doing something invalid or is this version just not quite up to the task?
Hmmmm, can't convert from type A to non-scalar type A? What's that mean? o.O
No, that's not a conversion to the same type. Despite having identical bodies, the different lambdas have different types. Newer versions of GCC make this clearer, and give the error message:
error: conversion from '__lambda1' to non-scalar type '__lambda0' requested
clang does even better:
error: no viable conversion from '<lambda at test.cc:2:18>' to 'decltype(x)' (aka '<lambda at test.cc:1:10>')
I can use std::function to get this to work, but a problem with that is it doesn't seem to work with tuple:
It does (with 4.5.4, at least, I don't have 4.5.3 to test), but your initialisation isn't quite right.
tuple<int, function<void()>> stdTuple1 {1, [](){}}; // lose the = to initialise stdTuple1 directly
I'm not sure about the state of n3043 in 4.5.3, but you should be able to use function pointer conversion. If I'm not misunderstanding your usage intentions, this may work for you;
void (*x)();
decltype(x) fn = [](){};
decltype(x) jmpTable[] = { [](){}, [](){} };