Cmake did not use C++11 flag using CXX_STANDARD?

Question

I'm fairly new to cmake and I'm trying to use the mongodb driver for C++ by using this tutorial: https://mongodb.github.io/mongo-cxx-driver/mongocxx-v3/tutorial/. The tutorial says you need C++11, so I tried the recommended way which is using CXX_STANDARD property. But it didn't work. I finally gave up and used add_definitions() and it worked!

The cmake file shows both approaches I tried. ie, add_definitions and the set property approach in the comment (which I tried first but failed to work).

It works with add_definitions() now, but everywhere I turn people recommend using CXX_STANDARD or let cmake use C++11 automatically by requesting a C++11 feature.

So, will this be a problem later on for some reason? And why didn't it work the first time around?

My cmake file:

cmake_minimum_required(VERSION 3.2)

project(testproj CXX)

file(GLOB SRC src/*.cpp)

add_library(testproj SHARED ${SRC})

add_definitions(--std=c++11)
#set(TARGET testproj PROPERTY CXX_STANDARD 11)
#set(TARGET testproj PROPERTY CXX_STANDARD_REQUIRED ON)

# include directories
include_directories(/usr/local/include/mongocxx/v_noabi)
include_directories(/usr/local/include/libmongoc-1.0)
include_directories(/usr/local/include/bsoncxx/v_noabi)
include_directories(/usr/local/include/libbson-1.0)

# library path
link_directories(/usr/local/lib)
target_link_libraries(testproj mongocxx bsoncxx)

Your `set(TARGET testproj PROPERTY CXX_STANDARD 11)` line is commented out. Is that deliberate? — Lightness Races in Orbit, Mar 30 '17 at 14:19
Yes, I left it in to show how I attempted it the first time. I'll edit my question to make it clearer. — Raghuveer, Mar 30 '17 at 14:21
Yes, show us the code you're asking about, not some other code. — Lightness Races in Orbit, Mar 30 '17 at 14:21
@malat: I don't think so. The OP doesn't even mention `CMAKE_CXX_STANDARD`. — Lightness Races in Orbit, Mar 30 '17 at 14:32
@malat Neither the question nor the answer of the marked duplicate make any mention of `add_definitions()` or `set(TARGET testproj PROPERTY CXX_STANDARD 11)`. If anything, it is a duplicate of one of these - http://stackoverflow.com/q/10851247/5209610, http://stackoverflow.com/q/37621342/5209610. — Vladislav Martin, Mar 30 '17 at 14:39
It is almost a duplicate. On closer inspection after following those links, the set() was supposed to be set_property(). set() is for variables, set_property() is for cmake properties. Change that and it works. Thanks everyone. — Raghuveer, Mar 30 '17 at 14:45

score -1 · Answer 1 · answered Mar 30 '17 at 14:24

-1

It would be better to define the c++11 flag to the whole project.

To do so, you can use the variable CMAKE_CXX_FLAGS to set it as a global flag, like this :

set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11")

Since it´s a global call, I recommand you to put it just beneath the project line.

answered Mar 30 '17 at 14:24

bl4ckb0ne

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Better yet: `target_compile_features( mydemo PRIVATE cxx_std_17 )` – Victor Eijkhout Apr 18 '23 at 14:47

Cmake did not use C++11 flag using CXX_STANDARD?

1 Answers1