Cmake compilation option setting in ros2

There are many compilation options , Here are some common compilation option settings , And explain the function .

Designated to use C++ edition

set(CMAKE_CXX_STANDARD 17)

It can be set as required 11, 14, 17, 20 wait C++ edition .

Set compilation options

add_compile_options(-Wall -Wextra -Wpedantic -Wno-unused-parameter -g)

Alarm options ：

Alarm options	Function description
-Wall	Allow to issue gcc All the useful alarm information provided
-Wextra	Warn all legitimate but questionable expressions
-Werror	Treat alarm information as error information
-pedantic	Allow to issue ANSI C All warning messages listed in the standard
-w	Turn off all warnings （ It is not recommended to use ）
-Wfatal-errors	Stop on the first error , Reduce error finding time

We often see the following error messages after we add that the alarms turn into errors .

error: unused parameter ‘test’ [-Werror=unused-parameter]

error: variable 'begin' set but not used [-Werror=unused-but-set-variable]

There are places where variables are set but not used , You can add the following code to eliminate this type of error .

#define UNUSED(x) (void)(x)

Code generation options ：

Code generation options	Description of options
-fPIC	When compiling dynamic libraries , Require position independent code generation (Position-Independent Code). That is, the absolute address is not used in the code , And using relative addresses , So the loader can load it anywhere in memory and execute . If not used -fPIC, The generated code contains the absolute address . When the loader loads it , We need to reposition first , Relocation modifies the content of the snippet , So each process generates a copy of the code snippet .
-fvisibility=default or hidden	By default , Set up ELF The visibility of the symbol in the image is public or hidden. The default value is default.hidden Can significantly improve the performance of linking and loading shared libraries , Generate more optimized code , Provide near perfect API Output and prevent symbol collisions . It is strongly recommended to use it when compiling shared libraries .

Code optimization options ：

Optimization options	Description of options
-O0	No optimization . This is the default
-O1	Try to optimize compile time and executable size .
-O2	Try almost all the optimizations , But not “ Space for time ” Optimization method .
-O3	Turn on some more optimization options ：-finline-functions, -funswitch-loops and -fgcse-after-reload .
-O	Equivalents and -O1
-Os	Optimize the size of the generated file . open -O2 Open all the options , Except for those that increase the file size .
-fomit-frame-pointer	Remove all functions SFP（Stack Frame Pointer）, That is, the stack frame pointer is not saved when the function is called SFP. Can improve the speed of the program , The price is not to pass backtrace debug .
-fno-omit-frame-pointer	And -fno-omit-frame-pointer contrary

Be careful ： -O1 open -fomit-frame-pointer Options

Be careful ： No special needs , Optimization options can also be set independently , Directly set the following Compile type that will do

Debug Options ：

Debug Options	Description of options
-g	Generate object code with debug information
-ggdb	Generate gdb specially Debug information with , There will be some. gdb Dedicated extensions
-gdwarf-2	produce DWARF version2 Debug information in the format of

Be careful ： No special needs ,Debug Options can also be set independently , Directly set the following Compile type that will do

Set compilation type

Specify , As shown below ：

colcon build --cmake-args '-DCMAKE_BUILD_TYPE=RelWithDebInfo'

There are four types of compilation ：

Compile type	Type description	Similar to option set
Debug	Code optimization is turned off , Added code debugging information , Increased the warning level	-O0 -g -Wall -D_DEBUG
Release	The program achieves the best performance , The fastest , But a lot of debugging information is lost	-O2 -DNDEBUG
RelWithDebInfo	This mode will try to follow Release Pattern compilation of , But it still carries debugging information , It is a compromise between speed and debugging information .	-O0 -ggdb -DNDEBUG
MinSizeRel	Minimize the size of the execution file , Generally used in embedded scenes	-O1 -DNDEBUG -DMIN_SIZE_REL

Additional explanation ：

DCMAKE_BUILD_TYPE Configuration and g++ The relationship between compilation options ：

DCMAKE_BUILD_TYPE yes Cmake Things on the configuration level . The relevant configuration of the final compiled type will be converted to g++ Compilation options .

Reference resources ：

https://blog.51cto.com/u_15169172/2710502

---

If you think it's useful, just praise it ！

It's me , One to help everyone Filling pit Robot development siege lion .

In addition, the official account. 《 First flight 》 Internal reply “ robot ” Get carefully recommended C/C++,Python,Docker,Qt,ROS1/2 And other commonly used technical data in the robot industry .