Build error SystemC 2.3.3 with C++17

[sheridp@umich.edu]

The following Dockerfile will reproduce the problem:

FROM alpine:3.9 as builder

RUN apk add --no-cache build-base linux-headers

WORKDIR /opt

FROM builder as builder_systemc

COPY systemc-2.3.3.gz /opt

RUN mkdir /opt/systemc_src && \
    tar -xf systemc-2.3.3.gz -C /opt/systemc_src --strip-components=1 && \
    cd /opt/systemc_src && ./configure --prefix /opt/systemc-2.3.3 --enable-debug CXXFLAGS="-DSC_CPLUSPLUS=201703L" && \
    make -j$(nproc) && \
    make install

Which results in the following error:

  CXX      kernel/sc_simcontext.lo
In file included from kernel/sc_simcontext.cpp:57:
../../src/sysc/utils/sc_string_view.h:62:29: error: 'string_view' in namespace 'std' does not name a type
 typedef SC_STRING_VIEW_NS_::string_view sc_string_view;
                             ^~~~~~~~~~~

It looks like the following is related:

#if SC_CPLUSPLUS >= 201402L && defined(__has_include)
#  if SC_CPLUSPLUS > 201402L && __has_include(<string_view>) /* since C++17 */
#    define SC_STRING_VIEW_NS_ std
#    include <string_view>
   /*  available in Library Fundamentals, ISO/IEC TS 19568:2015 */
#  elif __has_include(<experimental/string_view>)
#    define SC_STRING_VIEW_NS_ std::experimental
#    include <experimental/string_view>
#  endif
#else
// TODO: other ways to detect availability of std::(experimental::)string_view?
#endif

I'm guessing that defining SC_CPLUSPLUS did not cause the -std=c++17 flag to be passed to the compiler, because <string_view> contains the following:

#if __cplusplus >= 201703L

 

Update:

Modifying the ./configure command to:

./configure --prefix /opt/systemc-2.3.3 --enable-debug CXXFLAGS="-DSC_CPLUSPLUS=201703L -std=c++17"

solves the problem. 

It might be worthwhile mentioning this in the INSTALL notes.

[Philipp A Hartmann]

The INSTALL notes currently say the following about the SC_CPLUSPLUS preprocessor switch (emphasis mine):

Quote

 

This setting allows downgrading the assumed version of the underlying C++ standard on the current platform.  By default, the latest supported version is chosen.

Supported values are

• SC_CPLUSPLUS=199701L (C++03, ISO/IEC 14882:1998, 14882:2003)
• SC_CPLUSPLUS=201103L (C++11, ISO/IEC 14882:2011)
• SC_CPLUSPLUS=201402L (C++14, ISO/IEC 14882:2014)
• SC_CPLUSPLUS=201703L (C++17, ISO/IEC 14882:2017)

 

This means, that you can explicitly opt-out of some SystemC features, that would generally be supported by your compiler's C++ language support.  Selecting a newer C++ standard version than supported by your compiler (setup) will typically not work - as you have experienced.

That said, adding a preprocessor flag on the compiler command-line does not affect the language mode of the compiler.  How to switch your compiler to C++17 mode is outside of the scope of SystemC.  Your compiler (version) seems to require the -std=c++17 switch to enable this mode.  The SC_CPLUSPLUS flag is then not needed as it will be set automatically to the selected version.

Hope that helps,
  Philipp

[sheridp@umich.edu]

Hi Philipp,

Thanks for your response.  You are right, I think the spec is clear on that point.  I think I had some confusion regarding the default flags on the compiler, but, as you pointed out, that is beyond the scope of the SystemC spec.

[Grisha]

On 3/15/2019 at 11:12 PM, sheridp@umich.edu said:

It might be worthwhile mentioning this in the INSTALL notes.

+1. I tried to understand why I can't build under c++14 very long. Until I found this post. Thank you.

[Soumyajeet]

On 3/16/2019 at 3:33 PM, Philipp A Hartmann said:

The INSTALL notes currently say the following about the SC_CPLUSPLUS preprocessor switch (emphasis mine):

This means, that you can explicitly opt-out of some SystemC features, that would generally be supported by your compiler's C++ language support.  Selecting a newer C++ standard version than supported by your compiler (setup) will typically not work - as you have experienced.

That said, adding a preprocessor flag on the compiler command-line does not affect the language mode of the compiler.  How to switch your compiler to C++17 mode is outside of the scope of SystemC.  Your compiler (version) seems to require the -std=c++17 switch to enable this mode.  The SC_CPLUSPLUS flag is then not needed as it will be set automatically to the selected version.

Hope that helps,
  Philipp

Hello Philipp,
May I know what is the state of C++20 support for SystemC? When I tried to build a project with C++20 I got a linker error. I tried to find a suitable preprocessor switch for C++20 in the INSTALL notes but there isn't any. Kindly let me know.