Error expected nested name specifier before system

Error expected nested name specifier before namespace

I may simply be too tired, so I’m not figuring this out. I’m working with templates for the first time. I’ve developed an algorithm to accept a function given an arbitrary number of variables (passed through an array) and numerically differentiate it an arbitrary number of times. I’m trying to template it so that it can pass and receive a few combinations of double and long double types. I’m also trying to implement the explicit instantiation as described in http://www.cplusplus.com/forum/articles/14272/ .

Line 38: Error: expected nested-name-specifier before ‘dn_dxn’
Line 38: Error: template-id ‘dn_dxn ‘ used as declarator
Line 38: Error: ‘dn_dxn(unsigned int, T (*)(U*), U*, unsigned int)’ is not a variable template
(Analogous errors for the remaining templates.)

template <> double dn_dxn( unsigned int n, double (*f)( double []), double args[], unsigned int narg);

But wouldn’t you be better just defining the entire template function in the .h file?

These are function templates; a few explicit instantiation declarations and definitions would be:

Thank you. I wasn’t putting the full function in the .h file because, as I’ve understood it from my formal programming classes, writing executed code in a header is considered bad practice.

However, I still have problems. Using the format above, I now get the error in the header «error: ‘dn_dxn’ is not a template function. In the .cpp, I’m getting «error: there is no arguments to ‘nCr’ that depend on a template parameter, so a declaration of ‘nCr’ must be available [-fpermissive]»

> I wasn’t putting the full function in the .h file because, as I’ve understood it from my formal
> programming classes, writing executed code in a header is considered bad practice.

It is ok for to define function templates in the header.

A function template by itself is not a type, or a function, or any other entity. No code is generated from a source file that contains only template definitions. In order for any code to appear, a template must be instantiated: the template arguments must be determined so that the compiler can generate an actual function (or class, from a class template).

https://en.cppreference.com/w/cpp/language/function_template

Place the template definitions in the header, and let the templates be implicitly instantiated (unless there is a specific reason not to do so).

As an aside, avoid specialising function templates with template<>, it is almost always a bad idea.
See: http://www.gotw.ca/publications/mill17.htm

Sorry, @rcx11, I was incorrect to put the angle brackets in: @JLBorges gives the correct syntax and arrangement between .h and .cpp files.

I usually put templates in the .h file and don’t have to worry about the explicit instantiations, so I simply got it wrong in this instance.

Thank you, all. This is coming together but I’m still receiving «Line 16: error: there is no arguments to ‘nCr’ that depend on a template parameter, so a declaration of ‘nCr’ must be available [-fpermissive]». Thoughts?

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Error expected nested name specifier before namespace

#include «DicomImageReader.h»
#include «ImageSliceViewer.h»
#include «upmcDocument.h»

template
class DicomSeriesBase : public UPMC::Document
<
public:
DicomSeriesBase();
public:

typedef typename itk::Image VolumeType;

typedef typename itk::Image ImageType;

typedef typename itk::ImageFileReader VolumeReaderType;

typedef typename ISIS::DicomImageReader DicomReaderType;

typedef typename itk::Image VisualizationVolumeType;

typedef typename itk::RescaleIntensityImageFilter RescaleIntensityFilterType;

typedef typename itk::ImageToVTKImageFilter ITK2VTKAdaptorFilterType;

typedef typename itk::ThresholdImageFilter ThresholdFilterType;

public:
bool isLoaded();
vtkImageData * GetVTKImageData();
typename VolumeType::ConstPointer GetLoadedVolume();

protected:
double m_SeedPoint[3];

typename VolumeReaderType::Pointer m_VolumeReader;

typename RescaleIntensityFilterType::Pointer m_RescaleIntensity;

typename ITK2VTKAdaptorFilterType::Pointer m_ITK2VTKAdaptor;

typename RescaleIntensityFilterType::Pointer m_SegmentedVolumeRescaleIntensity;

typename ITK2VTKAdaptorFilterType::Pointer m_LoadedVolumeITK2VTKAdaptor;
typename DicomReaderType m_DicomVolumeReader;

typename VolumeType::ConstPointer m_LoadedVolume;

typename DicomReaderType::ReaderType::DictionaryArrayType m_metaDictionary;

> //namespace UPMC

With gcc-4.3.3 I get the following error:

Line 107 is:

Thanks in advance.
_________________
John

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error: expected nested-name-specifier

I try to compile a 2 years old project (successfully compiled with g++
3.3, if I correctly remember ).

But get problems now with g++ -gcc 4.2.3 :

template
class ListPtr;

template
class ListPtrIterator <

public:
ListPtrIterator( ListPtr * _user ):
M_user( _user ),
M_cur( M_user->begin() ) <>

bool
reset( void ) <
M_cur =M_user->begin();
return M_cur!=M_user->end();
>

private:
ListPtr * M_user;
typename list ::iterator M_cur;
^^^^
ERROR: expected nested-name-specifier before ‘list’
>;

Please do you know what’s the problem ?
Has something changed in «typename» syntax ?

using namespace std;

Regards, Ron AF Greve

template
class ListPtr;

template
class ListPtrIterator <

public:
ListPtrIterator( ListPtr * _user ):
M_user( _user ),
M_cur( M_user->begin() ) <>

bool
reset( void ) <
M_cur =M_user->begin();
return M_cur!=M_user->end();
>

private:
ListPtr * M_user;
typename list ::iterator M_cur;
^^^^
ERROR: expected nested-name-specifier before ‘list’
>;

Please do you know what’s the problem ?
Has something changed in «typename» syntax ?

I try to compile a 2 years old project (successfully compiled with g++
3.3, if I correctly remember ).

But get problems now with g++ -gcc 4.2.3 :

typename list ::iterator M_cur;
^^^^
ERROR: expected nested-name-specifier before ‘list’
>;

Should be std::list

Old gcc versions accepted standard containers in the global namespace.

Ron AF Greve wrote:

[please don’t top post]

using namespace std;
in your code?

Nor should you, if this is from a header.

hash_map is a sgi extension AFAIK. I believe it is now located somewhere
else (then again you might have used a -I ext switch of course).

Regards, Ron AF Greve

«Ron AF Greve» Hi,

I try to compile a 2 years old project (successfully compiled with g++
3.3, if I correctly remember ).

But get problems now with g++ -gcc 4.2.3 :

template
class ListPtr;

template
class ListPtrIterator <

public:
ListPtrIterator( ListPtr * _user ):
M_user( _user ),
M_cur( M_user->begin() ) <>

bool
reset( void ) <
M_cur =M_user->begin();
return M_cur!=M_user->end();
>

private:
ListPtr * M_user;
typename list ::iterator M_cur;
^^^^
ERROR: expected nested-name-specifier before ‘list’
>;

Please do you know what’s the problem ?
Has something changed in «typename» syntax ?

Thanks a lot for the explanations !

Yes, std:: perfectly solves the issue.

Thanks to have spoken about the changing of behaviour of gcc : the
makefile compiled before.
However I’m not surprised to run into problems in trying to build
this old project : because there were ugly things to be able to make
different gcc cope with SGI extensions.

Thanks a lot for the explanations !

Yes, std:: perfectly solves the issue.

Thanks to have spoken about the changing of behaviour of gcc : the
makefile compiled before.
However I’m not surprised to run into problems in trying to build
this old project : because there were ugly things to be able to make
different gcc cope with SGI extensions.

You will often find ugly things to get different gcc versions to cope
with other gcc versions!

Make sure you invoke the compiler in its standard conforming mode, to
save yourself problems in the future.

Make sure you invoke the compiler in its standard conforming mode, to
save yourself problems in the future.

Thanks for the advice !

Now that all sources successfully compiles with gcc 4.2.3., I get lot
of linker errors that complains about dozens of undefined references
to stl internals.
Here is the first one :

cvtChar.o: In function `escape(char)’:
cvtChar.c++:(.text+0x53c): undefined reference to
`stlpmtx_std::__node_alloc::_M_deallocate(void*, unsigned int)’

I add a -llibstlport to the Makefile libraries but dunno : remains
stuck.
I’m absolutely sure that the last time I built this project nothing
additional was required for the link.

Then I tried to build a stl-manual example : same kind of linker
error.
I’ve not used C++ for about one year but remember not to have such
kind of problems with old compiler versions.

Please do you have an idea about how to make the libstlport be found
at link stage ?
The packages :
libstlport4.6c2
libstlport5.1
libstlport5.1-dev
are installed on this Debian Sid.
Maybe is there a problem about different runtime libraries ?

>You will often find ugly things to get different gcc versions to cope
with other gcc versions!

Make sure you invoke the compiler in its standard conforming mode, to
save yourself problems in the future.

Thanks for the advice !

Now that all sources successfully compiles with gcc 4.2.3., I get lot
of linker errors that complains about dozens of undefined references
to stl internals.
Here is the first one :

cvtChar.o: In function `escape(char)’:
cvtChar.c++:(.text+0x53c): undefined reference to
`stlpmtx_std::__node_alloc::_M_deallocate(void*, unsigned int)’

You have stayed into the realms of gcc or Linux specific problems I’m
afraid. You should be able to get help from a Linux of gcc group.

afraid. You should be able to get help from a Linux of gcc group.

You probably are right, will ask the question in a Linux forum.

Try out ldd command to find out if you are linking to the correct
library.

-llibstlport might not just be sufficient in that you would
need to tell the LIB_PATH,LD_LIBRARY_PATH (whatever your compiler
understands) as well about where the library is (not just the
includes).

About this you are certainly right. I perform some trials.

Leaved stlport5.1 and went back to 4.6..
Things ended to successfully build.
The link stage :
g++ -O3 -I /usr/include/stlport -lreadline -o k /usr/lib/
libstlport_gcc.so cvtChar.o readline.o input.o Form.o Overload.o
read.o eval.o print.o banner.o repl.o keywords.o

Were specifying stl lib this way, like a «.o» /usr/lib/
libstlport_gcc.so is absolutely ugly.
I don’t worry about this : I just needed to build the executable and
maybe to add small changes on it to print some internals. This just to
understand how it works.

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Error: expected nested-name-specifier before ‘dn_dxn’

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#ifndef HAM_H
#define HAM_H

// Functions for solving non-linear systems using Homotopy Analysis Method

template <typename T, typename U> T dn_dxn(unsigned int n, T (*f)(U[]), U args[], unsigned int narg);
template <typename T, typename U> T nCr(T n, U k);
template <typename T> T factorial(T n);

#endif // HAM_H 

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#include <cmath>
#include "HAM.h"

//num_t dn_dxn(level of differentiation, base function, base function argument array, which argument to differentiate)
template <typename T, typename U>
T dn_dxn(unsigned int n, T (*f)(U[]), U args[], unsigned int narg)
{
    T h = pow(1e-9, 1 / n);  // Smallest reasonable change in x; Value determined by experimentation.
    T sum = 0;

    for (unsigned int k = 0; k <= n; k++)
    {
        args[narg] += (n / 2 - k) * h;
        sum += pow(-1, k) * nCr(n, k) * f(args);
        args[narg] -= (n / 2 - k) * h;
    }

    return sum / pow(h, n);
}

template <typename T, typename U>
T nCr(T n, U k)
{
    return factorial(n) / (factorial(k) * factorial(n - k));
}

template <typename T>
T factorial(T n)
{
    if (n < 0)
        return NAN;
    else if (n == 0)
        return 1;
    else
        return(n * factorial(n-1));
}

template typename dn_dxn<long double, long double>;
template typename dn_dxn<long double, double>;
template typename dn_dxn<double, long double>;
template typename dn_dxn<double, double>;

template typename nCr<unsigned int, unsigned int>;
template typename nCr<unsigned int, unsigned long>;
template typename nCr<unsigned long, unsigned int>;
template typename nCr<unsigned long, unsigned long>;

template typename factorial<unsigned int>;
template typename factorial<unsigned long>;

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// explicit instantiation declarations (in the header)

extern template unsigned long factorial( unsigned long ) ;
extern template unsigned int nCr( unsigned int, unsigned int );
extern template double dn_dxn( unsigned int, double(*)(double[]), double[], unsigned int ) ;

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// explicit instantiation definitions (in the cpp file)

template unsigned long factorial( unsigned long ) ;
template unsigned int nCr( unsigned int, unsigned int );
template double dn_dxn( unsigned int, double(*)(double[]), double[], unsigned int ) ;

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#ifndef HAM_H
#define HAM_H

// Functions for solving non-linear systems using Homotopy Analysis Method

//num_t dn_dxn(level of differentiation, base function, base function argument array, which argument to differentiate)
template <typename T, typename U>
T dn_dxn(unsigned int n, T (*f)(U[]), U args[], unsigned int narg)
{
    T h = pow(1e-9, 1 / n);  // Smallest reasonable change in x; Value determined by experimentation.
    T sum = 0;

    for (unsigned int k = 0; k <= n; k++)
    {
        args[narg] += (n / 2 - k) * h;
        sum += pow(-1, k) * nCr(n, k) * f(args);
        args[narg] -= (n / 2 - k) * h;
    }

    return sum / pow(h, n);
}

template <typename T, typename U>
T nCr(T n, U k)
{
    return factorial(n) / (factorial(k) * factorial(n - k));
}

template <typename T>
T factorial(T n)
{
    if (n < 0)
        return NAN;
    else if (n == 0)
        return 1;
    else
        return(n * factorial(n-1));
}

#endif // HAM_H 

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#ifndef HAM_H
#define HAM_H

#include <cmath> // for std::pow

// Functions for solving non-linear systems using Homotopy Analysis Method

//////////////// added /////////////////////////////////////
template <typename T, typename U> T nCr(T n, U k) ;
template <typename T> T factorial(T n) ;
////////////////////////////////////////////////////////////

//num_t dn_dxn(level of differentiation, base function, base function argument array, which argument to differentiate)
template <typename T, typename U>
T dn_dxn(unsigned int n, T (*f)(U[]), U args[], unsigned int narg)
{
// ... 

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#include <iostream>
#include <type_traits> // https://en.cppreference.com/w/cpp/types/is_integral

// enabled if and only if INT_TYPE is an integral type
template < typename INT_TYPE > constexpr
 typename std::enable_if< std::is_integral<INT_TYPE>::value, unsigned long long >::type
factorial( INT_TYPE n )
{ return n < 2 ? 1 : n * factorial(n-1) ; }

// static assertion fails if INT_TYPE is not an integral type
template < typename INT_TYPE > constexpr
unsigned long long factorial_2( INT_TYPE n )
{
    static_assert( std::is_integral<INT_TYPE>::value, "an integral type is required" ) ;
    return n < 2 ? 1 : n * factorial_2(n-1) ;
}

int main()
{
    std::cout << factorial(12) << 'n' ; // 479001600
    std::cout << factorial_2(12) << 'n' ; // 479001600

    std::cout << factorial(-3) << 'n' ; // 1
    std::cout << factorial_2(-3) << 'n' ; // 1

    // factorial(10.3) ; // *** error: no matching function
    // factorial_2(10.3) ; // *** error: static_assert failed: "an integral type is required"
}

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#include «DicomImageReader.h»

#include «ImageSliceViewer.h»

#include «upmcDocument.h»

namespace UPMC {

template< class TPixelType, class TVisualizationPixelType >

class DicomSeriesBase : public UPMC::Document

{

public:

   DicomSeriesBase();

public:

   typedef typename itk::Image<  TPixelType, 3 >            VolumeType;

   typedef typename itk::Image<  TPixelType, 2 >            ImageType;

   typedef typename itk::ImageFileReader< VolumeType >         VolumeReaderType;

   typedef typename ISIS::DicomImageReader< VolumeType >      DicomReaderType;

   typedef typename itk::Image< TVisualizationPixelType, 3 >   VisualizationVolumeType;

   typedef typename itk::RescaleIntensityImageFilter<

      VolumeType,

      VisualizationVolumeType >                        RescaleIntensityFilterType;

   typedef typename itk::ImageToVTKImageFilter<

      VolumeType >                                 ITK2VTKAdaptorFilterType;

   typedef typename itk::ThresholdImageFilter< VolumeType >   ThresholdFilterType;

public:

   bool                                          isLoaded();

   vtkImageData *                                    GetVTKImageData();

   typename VolumeType::ConstPointer                     GetLoadedVolume();

protected:

   double                                          m_SeedPoint[3];

   int                                             m_SeedIndex[3];

   double                                          m_SeedValue;

   typename VolumeReaderType::Pointer                     m_VolumeReader;

   typename RescaleIntensityFilterType::Pointer            m_RescaleIntensity;

   typename ITK2VTKAdaptorFilterType::Pointer               m_ITK2VTKAdaptor;

   typename RescaleIntensityFilterType::Pointer            m_SegmentedVolumeRescaleIntensity;

   typename ITK2VTKAdaptorFilterType::Pointer               m_LoadedVolumeITK2VTKAdaptor;

   typename DicomReaderType                           m_DicomVolumeReader;

   typename VolumeType::ConstPointer                     m_LoadedVolume;

   typename DicomReaderType::ReaderType::DictionaryArrayType   m_metaDictionary;

};

} //namespace UPMC

Hi,

I need instruction how to use the System.Management in Dev-cpp. I would like
to get some informations from WMI such as: Processor_ID, HDD_ID, MAINBOARD_ID.

Can anybody give me the step by step information how to obtain informations
like that from WMI under DEV-C++ compilator?

I have version 4.9.9.2 of DEV-C++

The sample code I would like to use in DEV-C++ is:

«
using System;
using System.Management;
using System.Windows.Forms;

namespace WMISample
{
public class MyWMIQuery
{
public static void Main()
{
try
{
ManagementObjectSearcher searcher =
new ManagementObjectSearcher(«rootCIMV2»,
«SELECT * FROM Win32_Processor»);

foreach (ManagementObject queryObj in searcher.Get())
{
Console.WriteLine(«————————————«);
Console.WriteLine(«Win32_Processor instance»);
Console.WriteLine(«————————————«);
Console.WriteLine(«ProcessorId: {0}», queryObj);
}
}
catch (ManagementException e)
{
MessageBox.Show(«An error occurred while querying for WMI data: » +
e.Message);
}
}
}
}
»

… but it does not work on DEV-CPP

I got the ERROR COMPILE CODE AS FOLLOWING:

«
Kompilator: Default compiler
Building Makefile: «C:Dev-Cpptest_WMIMakefile.win»
Wykonywanie make…
make.exe -f «C:Dev-Cpptest_WMIMakefile.win» all
g++.exe -c main_wmi_test.cpp -o main_wmi_test.o -I»C:/Dev-
Cpp/lib/gcc/mingw32/3.4.2/include» -I»C:/Dev-Cpp/include/c++/3.4.2/backward»
-I»C:/Dev-Cpp/include/c++/3.4.2/mingw32″ -I»C:/Dev-Cpp/include/c++/3.4.2″ -I»C
:/Dev-Cpp/include» -I»C:/Dev-Cpp/WMI»

main_wmi_test.cpp:1: error: expected nested-name-specifier before «System»
main_wmi_test.cpp:1: error: System' has not been declared
main_wmi_test.cpp:2: error: expected nested-name-specifier before "System"
main_wmi_test.cpp:2: error:System’ has not been declared

main_wmi_test.cpp:2: error: expected ;' before '.' token
main_wmi_test.cpp:2: error: expected unqualified-id before '.' token
main_wmi_test.cpp:2: error: expected,’ or ;' before '.' token
main_wmi_test.cpp:3: error: expected nested-name-specifier before "System"
main_wmi_test.cpp:3: error:System’ has not been declared
main_wmi_test.cpp:3: error: expected `;’ before ‘.’ token
main_wmi_test.cpp:3: error: expected unqualified-id before ‘.’ token
»

I don’t know how to repair it.

Rgds,