Error expected nested name specifier before namespace

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:

Код:

LungAnalysis/src/main.cxx In file included from /home/john/projects/LungAnalysis/Include/DicomSeries.h:50, from /home/john/projects/LungAnalysis/src/main.cxx:48: /home/john/projects/LungAnalysis/Include/DicomSeriesBase.h:107: error: expected nested-name-specifier before ‘DicomReaderType’ /home/john/projects/LungAnalysis/Include/DicomSeriesBase.h:107: error: expected ‘;’ before ‘m_DicomVolumeReader’ In file included from /home/john/projects/LungAnalysis/Include/DicomSeriesBase.h:121, from /home/john/projects/LungAnalysis/Include/DicomSeries.h:50,

Line 107 is:

Код:

typename DicomReaderType m_DicomVolumeReader;

Thanks in advance.
_________________
John

Последний раз редактировалось: drescherjm (вс фев 08, 2009 5:08 pm), всего редактировалось 1 раз Вернуться к началу

TNorthover
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Добавлено: вс фев 08, 2009 4:32 pm Заголовок сообщения:
The typename isn’t necessary on that line because the standard assumption is that an identifier in that position is a type. g++ seems to be complaining because it expects any typename declaration there to be qualified (i.e. A::B). I don’t know enough to say whether this is in the standard or g++ being over-pedantic.

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drescherjm
Advocate

Зарегистрирован: 05 июн 2004
Сообщений: 2788
Откуда: Pittsburgh, PA, USA

Добавлено: вс фев 08, 2009 5:07 pm Заголовок сообщения:

Thanks. Before this project I never used typename but after upgrading to VisualStudio 2005 it complained and required that in many places where older compilers did not care. After removing typename on this line only that error is gone. Your explanation is very helpful with that. At one point I commented that line out the following line was still good: Код: typename DicomReaderType::ReaderType::DictionaryArrayType m_metaDictionary; As a result, I was confused at why DicomReaderType was good in one case but bad in another. You cleared this up for me. Looks like I need to read the docs on typename again. _________________ John My gentoo overlay Instructons for overlay

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drescherjm
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Зарегистрирован: 05 июн 2004
Сообщений: 2788
Откуда: Pittsburgh, PA, USA

Добавлено: пн фев 09, 2009 3:12 pm Заголовок сообщения:
BTW. A few hours and a dozen or so fixes later all is well. The 3D Lung CT viewer now works at least as well in gentoo as it does in XP and now it does that with 64 bit code instead of being limited to only 32. Now time to work on the actual processing / analysis / cancer detection.. _________________ John My gentoo overlay Instructons for overlay

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Источник

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.

This discussion thread is closed

Replies have been disabled for this discussion.

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#include «itkImage.h»

#include «itkImageFileReader.h»

#include «itkImageToVTKImageFilter.h»

#include «itkRescaleIntensityImageFilter.h»

#include «itkImageFileWriter.h»

#include «itkThresholdImageFilter.h»

#include «itkImageSeriesReader.h»

#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

The ‘ERROR (expected nested-name-specifier before ‘namespace’)` error you may get while compiling your C++ code with a C++ compiler, this kind of issue might frustrate one, here we will discuss in the depth about the issue. 

Photo by Rachel Vine

TABLE OF CONTENTS

1. What is «ERROR (expected nested-name-specifier before ‘namespace’)»?
2. Why «ERROR (expected nested-name-specifier before ‘namespace’)» happens?
3. How to resolve «ERROR (expected nested-name-specifier before ‘namespace’)«:
   1. Solution:
4. Conclusion

What is  “ERROR (expected nested-name-specifier before ‘namespace’)”?

Before discussing the error, we should know, what is a nested name specifier?

C++ nested name specifiers are the prefixes to qualified names. For example, “foo::” in “foo::x” is a nested name specifier. Nested name specifiers are made up of a sequence of specifiers, each of which can be namespace, type, identifier (for dependent names), decltype specifier, or the global specifier (‘::’). The last two specifiers can only appear at the start of a nested-namespace-specifier.

#include 
#include 

template
class ListPtr;

template
class ListPtrIterator {

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

bool
cur( T*& );

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'
};

Output

new.cpp:28:46: warning: multi-character character constant [-Wmultichar]

 ERROR: expected nested-name-specifier before 'list'

Why does “ERROR (expected nested-name-specifier before ‘namespace’)“ happens?

As the compiler suggests that there is an with the list. Here the compiler does not accept the list as it is. Compiler accepts it as std::list.

As we know if we do not use the using namespace std in our program then we will face an error saying may be like that cout was not declared in this scope. But we know that in the past we did not need to define the using namespace std in the program. But now we have to use it or we have to use cout as std::cout. 

In the program given above the cause is pretty similar to this reason.

Following is the error message you get:

` main.cpp online 2:7: error: expected nested-name-specifier before ‘namespace’
 using namespace std;
       ^~~~~~~~~`

How to resolve “ERROR (expected nested-name-specifier before ‘namespace’)”?

Solution :

As I mentioned earlier, in the program given above the cause is pretty similar to this reason. So we have to use std::list to resolve the error since compilers do not accept containers without nested-name-specifier.

⚠️ Remember to use C++11 (otherwise you’ll receive an error saying that extended initializer lists are only available with -std=c++11 or -std=gnu++11)..

ℹ   Ensure that the relevant header files are included.

Conclusion:

 We discussed in this article about ERROR (expected nested-name-specifier before ‘namespace’) discussed and a number of solutions to get around it, one final way out may be be to upgrade to a more recent compiler version