Experimental Physics and
Industrial Control System

Michael Davidsaver via Tech-talk <tech-talk at aps.anl.gov> · Thu, 15 Jun 2023 10:26:28 -0700

On 6/13/23 10:47, Mark Rivers via Tech-talk wrote:

...
If I use the c++11 flag then I get this error:

|make[1]: Entering directory `/home/epics/devel/areaDetector-3-12-1/ADPICam/PICamApp/src/O.linux-x86_64'|

|/usr/bin/g++  -D_GNU_SOURCE -D_DEFAULT_SOURCE           -D_X86_64_  -DUNIX  -Dlinux      -O3 -g   -Wall     -std=c++11  -mtune=generic      -m64  -fPIC -I. -I../O.Common -I. -I. -I.. -I../../../include/compiler/gcc -I../../../include/os/Linux -I../../../include      -I/corvette/home/epics/devel/asyn-4-43/include     -I/corvette/home/epics/devel/areaDetector-3-12-1/ADSupport/include/os/Linux -I/corvette/home/epics/devel/areaDetector-3-12-1/ADSupport/include   -I/corvette/home/epics/devel/areaDetector-3-12-1/ADCore/include -I/corvette/usr/local/epics-devel/base-7.0.7/include/compiler/gcc -I/corvette/usr/local/epics-devel/base-7.0.7/include/os/Linux -I/corvette/usr/local/epics-devel/base-7.0.7/include        -c ../ADPICam.cpp|
|In file included from /usr/include/c++/4.8.2/bits/hashtable.h:35:0,|
|                 from /usr/include/c++/4.8.2/unordered_map:47,|

...

|/usr/include/c++/4.8.2/bits/hashtable_policy.h:1070:12: error: invalid use of incomplete type 'struct std::hash<PicamParameter>'|

As Matt mentioned, this is apparently a known issue with c++11
that std::hash<> didn't work out of the box for enum types
until c++14, which GCC 4.8 does not support (it didn't even
have complete support for c++11).

https://cplusplus.github.io/LWG/issue2148

https://en.cppreference.com/w/cpp/utility/hash

As a workaround you could either:

1) Use std::map when compiling with <= c++14

#if __cplusplus>=201402L
typedef std::unordered_map<PicamParameter, int> pcparam_map_t;
#else
typedef std::map<PicamParameter, int> pcparam_map_t;
#endif

2) provide your own specialization of std::hash

#if __cplusplus<201402L
namespace std {
template<>
struct hash<PicamParameter> {
    size_t operator()(PicamParameter v) {
        return std::hash((int)PicamParameter);
    }
};
}
#endif

3) Or switch the ordered_map to an 'int' key, and case the enum to 'int' everywhere

(probably the uglier of the three)

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System