Building demo not succeed

[wanghaEMQ]

When I built the project, an error happened.

I first build the nanosdk, and install it in my system. Then build the demo mqtt.

Here is log from ninja

➜  build git:(main) ✗ ninja 
[1/2] Building C object CMakeFiles/mqtt_client.dir/mqtt_client.c.o
../mqtt_client.c: In function ‘intHandler’:
../mqtt_client.c:58:2: warning: implicit declaration of function ‘nng_closeall’; did you mean ‘nng_close’? [-Wimplicit-function-declaration]
   58 |  nng_closeall();
      |  ^~~~~~~~~~~~
      |  nng_close
[2/2] Linking C executable mqtt_client
FAILED: mqtt_client 
: && /usr/bin/cc   -rdynamic CMakeFiles/mqtt_client.dir/mqtt_client.c.o  -o mqtt_client  -lnng  -lpthread && :
/usr/bin/ld: CMakeFiles/mqtt_client.dir/mqtt_client.c.o: in function `client_connect':
mqtt_client.c:(.text+0x221): undefined reference to `nng_mqtt_client_open'
collect2: error: ld returned 1 exit status
ninja: build stopped: subcommand failed.
➜  build git:(main) ✗ pwd
/home/wangha/docu/git/NanoSDK/demo/mqtt/build

My Env. Ubuntu 20.04 x86_64