Monday, February 20, 2017

Using Boost.Log in the project

Boost.Log, just like other module, it must be built first before it can be used. But most of the time I will just go for the default compilation, just like below

> ./b2 --with-log 

According to this documentation, I can have a lot more option to the build. Say for example -DBOOST_LOG_DYN_LINK, below is the definition of the macro:

BOOST_LOG_DYN_LINK If defined in user code, the library will assume the binary is built as a dynamically loaded library ("dll" or "so"). Otherwise it is assumed that the library is built in static mode. This macro must be either defined or not defined for all translation units of user application that uses logging. This macro can help with auto-linking on platforms that support it.

When I build with -DBOOST_LOG_DYN_LINK just like the sample below:

> ./b2 --with-log define=BOOST_LOG_DYN_LINK

I must have the following statement in the .pro file:


Take a closer look into the console output. Notice that BOOST_LOG_DYN_LINK option is added into g++ build command:
g++ -c -pipe -g -std=gnu++0x -Wall -W -D_REENTRANT -fPIC -DBOOST_LOG_DYN_LINK -DQT_QML_DEBUG 
-DQT_WIDGETS_LIB -DQT_GUI_LIB -DQT_CORE_LIB -I../../backupUtil -I. -I../../../tool/boost_1_61_0 -I../../backupUtil 
-I../../../tool/Qt5.6.0/5.6/gcc_64/include -I../../../tool/Qt5.6.0/5.6/gcc_64/include/QtWidgets 
-I../../../tool/Qt5.6.0/5.6/gcc_64/include/QtGui -I../../../tool/Qt5.6.0/5.6/gcc_64/include/QtCore -I. -I. 
-I../../../tool/Qt5.6.0/5.6/gcc_64/mkspecs/linux-g++ -o main.o ../main.cpp
If the above define statement is missing from the .pro file, the compiler will throw out the link error. Tracing that error could lead to a wrong way fixing the problem because the root cause wasn't there. This documentation would give some hints on how this thing could be fixed. Below is the important text from that documentation:
  • The <version> component describes the library major version. It is currently v2.
  • The <linkage> component tells whether the library is linked statically or dynamically. It is s if the library is linked statically and empty otherwise.
  • The <threading> component is st for single-threaded builds and mt for multi-threaded ones.
  • The <system> component describes the underlying OS API used by the library. Currently, it is only specified for multi-threaded builds. Depending on the target platform and configuration, it can be posix, nt5 or nt6.
Same to the default Boost.Log build without BOOST_LOG_LINK, link error will be throw if the define statement was declared in the .pro file.