invalid use of template-name ‘boost::asio::strand’ without an argument list

Question

I have an older program that I want to compile on Centos 8 with GCC 8.3.1. The make command looks like this:

CXXFLAGS = -O2 -std=c++11

all: my_prog

my_prog: my_prog.o
    g++ my_prog.o -o my_prog -lboost_filesystem -lboost_system -lsecond_level_include -lthird_level_include -lboost_regex -lboost_program_options `mysql_config --libs`

Here is the output for make :

In file included from /usr/local/include/redisclient/redissyncclient.h:16,
                 from /usr/local/include/third_level_include.hpp:11,
                 from /usr/local/include/second_level_include.hpp:40,
                 from my_prog.cpp:9:
/usr/local/include/redisclient/impl/redisclientimpl.h:72:5: error: invalid use of template-name ‘boost::asio::strand’ without an argument list
     boost::asio::strand strand;
     ^~~~~
/usr/local/include/redisclient/impl/redisclientimpl.h:72:5: note: class template argument deduction is only available with -std=c++17 or -std=gnu++17
In file included from /usr/local/include/redisclient/impl/redisclientimpl.h:13,
                 from /usr/local/include/redisclient/redissyncclient.h:16,
                 from /usr/local/include/third_level_include.hpp:11,
                 from /usr/local/include/second_level_include.hpp:40,
from my_prog.cpp:9:
/usr/include/boost/asio/strand.hpp:29:7: note: ‘template<class Executor> class boost::asio::strand’ declared here
 class strand
       ^~~~~~

[snip lots of output]

So I did what it suggested and replaced -std=c++11 with -std=gnu++17 and now I get this:

g++ -O2 -std=gnu++17   -c -o my_prog.o my_prog.cpp
In file included from /usr/local/include/redisclient/redissyncclient.h:16,
                 from /usr/local/include/third_level_include.hpp:11,
                 from /usr/local/include/second_level_include.hpp:40,
                 from my_prog.cpp:9:
/usr/local/include/redisclient/impl/redisclientimpl.h:72:5: error: invalid use of template-name ‘boost::asio::strand’ without an argument list
     boost::asio::strand strand;
     ^~~~~
make: *** [<builtin>: my_prog.o] Error 1

Considering that I'm not going to be changing the third party library code from Redis, is there a compiler flag or something I can use to make this error go away? The code compiled once upon a time with GCC 4.4.7 on Centos 6.

Answer 1

All executor interfaces have been upgraded a (long) while ago .

Strands used to be nested typedefs (and there is still one for "legacy" compatibility in io_service if that is enabled).

However, the new type succeeding is is boost::asio::strand<Executor> (so eg boost::asio::io_context::executor_type ). You can easily make a strand for any executor, eg:

 auto s = make_strand(io_object.get_executor()); 

What you are seeing is apparent mix-up of these names. I suspect it may have to do with

• local typedefs that alias strand
• local variables named strand (though I don't see immediately how that would lead to the exact message mposted)
• most likely: you have a using namespace that pulls in the new strand template

With this information, you should be able to sort it out.

Of course, had you posted the code, we could have shown it for you.