misc.md from README.md

Author: keineahnung2345

misc.md

@@ -0,0 +1,302 @@
+## Compile
+[Compiling with g++](https://www.geeksforgeeks.org/compiling-with-g-plus-plus/)
+
+### Check g++ default c++ standard version
+[Which C++ standard is the default when compiling with g++?](https://stackoverflow.com/questions/44734397/which-c-standard-is-the-default-when-compiling-with-g)
+```sh
+g++ -dM -E -x c++  /dev/null | grep -F __cplusplus
+```
+Sample output:
+```
+#define __cplusplus 199711L
+```
+
+### Compile, specify c++ version
+[to_string is not a member of std, says g++ (mingw)](https://stackoverflow.com/questions/12975341/to-string-is-not-a-member-of-std-says-g-mingw)
+```sh
+g++ xxx.cpp -std=c++11
+```
+
+This solves the error:
+```
+/usr/include/c++/5/bits/c++0x_warning.h:32:2: error: #error This file requires compiler and library support for the ISO C++ 2011 standard. This support must be enabled with the -std=c++11 or -std=gnu++11 compiler options.
+ #error This file requires compiler and library support \
+```
+
+### specify include directory
+```sh
+g++ xxx.cpp -I /usr/local/include
+```
+
+### make
+Dry run:
+
+[How do I force make/GCC to show me the commands?](https://stackoverflow.com/questions/5820303/how-do-i-force-make-gcc-to-show-me-the-commands)
+```sh
+make -n
+```
+
+### CMakeLists.txt
+#### fundamental
+
+```
+cmake_minimum_required(VERSION 3.5)
+project(name)
+# specify the c++ version to use
+set(CMAKE_CXX_STANDARD 14)
+
+set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wall -Wno-unused-result -Wno-unknown-pragmas -Wfatal-errors -fPIC -std=c++11")
+# the compiler flags for compiling C sources 
+message(STATUS "CMAKE_C_FLAGS: " ${CMAKE_C_FLAGS})
+# the compiler flags for compiling C++ sources 
+message(STATUS "CMAKE_CXX_FLAGS: " ${CMAKE_CXX_FLAGS})
+
+find_package(OpenCV REQUIRED)
+set(SOURCE_FILES ./src/file1.cpp ./src/file2.cpp)
+include_directories(${CMAKE_CURRENT_SOURCE_DIR}/include)
+link_directories(${CMAKE_SOURCE_DIR}/libs)
+
+# create a executable file
+add_executable(<executable_file_name> ./src/main.cpp)
+target_link_libraries(<executable_file_name> ${OpenCV_LIBS})
+
+# create a shared object
+add_library(<library_name> SHARED ${SOURCE_FILES})
+target_link_libraries(<library_name> ${OpenCV_LIBS})
+```
+
+Ref: [Configuring an c++ OpenCV project with Cmake](https://stackoverflow.com/questions/13970377/configuring-an-c-opencv-project-with-cmake)
+
+#### set variable and print
+[CMake: Output a list with delimiters](https://stackoverflow.com/questions/17666003/cmake-output-a-list-with-delimiters)
+```
+set(VAR1 hello)
+set(LIST1 a b c d)
+message("the variable VAR1 is " ${VAR1})
+message("the list LIST1 is " "${LIST1}")
+```
+
+Other types of variable: [What's the CMake syntax to set and use variables?](https://stackoverflow.com/questions/31037882/whats-the-cmake-syntax-to-set-and-use-variables)
+
+#### add definition
+This equals to add `#define MYVAR` in `.cpp` or `.h` files.
+```
+add_definitions(-D MYVAR)
+```
+
+#### CMAKE_SOURCE_DIR v.s. PROJECT_SOURCE_DIR
+[Are CMAKE_SOURCE_DIR and PROJECT_SOURCE_DIR the same in CMake?](https://stackoverflow.com/questions/32028667/are-cmake-source-dir-and-project-source-dir-the-same-in-cmake)
+
+`CMAKE_SOURCE_DIR`: the folder containing the top-level CMakeLists.txt
+
+`PROJECT_SOURCE_DIR`: the inner-most folder containing CMakeLists.txt with `project()` command
+
+#### project structure
+[CMake with include and source paths - basic setup](https://stackoverflow.com/questions/8304190/cmake-with-include-and-source-paths-basic-setup)
+
+### make, specify number of jobs as the number of processing units available
+```sh
+make -j $(nproc)
+```
+
+### cmake in debug mode and make in verbose mode
+[Using CMake with GNU Make: How can I see the exact commands?](https://stackoverflow.com/questions/2670121/using-cmake-with-gnu-make-how-can-i-see-the-exact-commands)
+```sh
+cmake -DCMAKE_BUILD_TYPE=DEBUG ..
+make VERBOSE=1 2>../log.txt
+```
+
+The `2>../log.txt` redirect error message into a log file.
+
+## list the .so dependencies of a executable file
+```sh
+ldd <executable>
+```
+Sample output:
+```
+	libudev.so.1 => /lib/x86_64-linux-gnu/libudev.so.1 (0x00007fc3364fd000)
+	libsoxr.so.0 => /usr/lib/x86_64-linux-gnu/libsoxr.so.0 (0x00007fc336297000)
+	libnuma.so.1 => /usr/lib/x86_64-linux-gnu/libnuma.so.1 (0x00007fc33608c000)
+```
+
+## list symbols from xxx.so
+```sh
+nm -D <xxx.so> # -D will list dynamic symbols
+```
+Sample output:
+```
+0000000000092030 T YoloPluginCtxInit
+                 U rename
+0000000000104d8f V _ZTS4Yolo
+000000000007c425 W _ZSt10_ConstructI7DsImageIEEvPT_DpOT0_
+```
+`T` for symbol defined in code section, `U` for undefined, `V` and `W` for weak object.
+
+This is helpful for solving the following error:
+```
+/home/ubuntu/catkin_ws/devel/lib/ros_trans/OpenTrans: symbol lookup error: /home/ubuntu/catkin_ws/devel/lib/libproduct.so: undefined symbol: YoloPluginGetVersion
+```
+
+## show the unmangled name of a symbol
+```sh
+c++filt <symbol(mangled name)>
+```
+
+## /usr/bin/ld: cannot find -l\<xxx>
+Error message while linking:
+```
+/usr/bin/ld: cannot find -lcudnn
+collect2: error: ld returned 1 exit status
+```
+Solution:
+[https://stackoverflow.com/questions/51451746/cmake-command-line-ld-library-path-and-c-include-dirs](https://stackoverflow.com/questions/51451746/cmake-command-line-ld-library-path-and-c-include-dirs)
+
+First set `LD_LIBRARY_PATH` to the path of that `.so` file, and then add:
+```
+link_directories( $ENV{LD_LIBRARY_PATH} )
+```
+into `CMakeLists.txt`.
+
+## ./a.out: error while loading shared libraries: xxx.so: cannot open shared object file: No such file or directory
+[g++ executable cannot find shared library](https://stackoverflow.com/questions/12000990/g-executable-cannot-find-shared-library)
+```sh
+LD_LIBRARY_PATH=/usr/local/lib ./a.out
+```
+or
+```sh
+export LD_LIBRARY_PATH=/usr/local/lib:$LD_LIBRARY_PATH
+```
+
+## stack smashing detected
+From [StackOverflow - Stack smashing detected](https://stackoverflow.com/questions/1345670/stack-smashing-detected/50690687), add the following in `CMakeLists` to temporarily get rid of this error:
+```
+set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -fno-stack-protector -std=c++11")
+```
+
+## c++: internal compiler error: Killed (program cc1plus)
+[make -j 8 g++: internal compiler error: Killed (program cc1plus)](https://stackoverflow.com/questions/30887143/make-j-8-g-internal-compiler-error-killed-program-cc1plus)
+
+That's probably `make -j4` uses to much memory, so it's killed by system, try using `make -j1` instead.
+
+Another method is to tell kswapd0 to only move stuff to SWAP when you are completely out of RAM([kswapd0 is taking a lot of cpu](https://askubuntu.com/questions/259739/kswapd0-is-taking-a-lot-of-cpu/530661)):
+```sh
+echo vm.swappiness=0 | sudo tee -a /etc/sysctl.conf
+```
+
+## specify CUDA path while cmake
+[How to let cmake find CUDA](https://stackoverflow.com/questions/19980412/how-to-let-cmake-find-cuda)
+
+Method 1, use `-D` flag while `cmake`:
+```sh
+cmake -D CUDA_TOOLKIT_ROOT_DIR=/usr/local/cuda ..
+```
+
+Method 2, revise `CMakeLists.txt`, before `FIND_PACKAGE(CUDA)`, add one line, this becomes:
+```
+set(CUDA_TOOLKIT_ROOT_DIR /usr/local/cuda)
+FIND_PACKAGE(CUDA)
+```
+
+## specify OpenCV path while cmake
+```
+set(OpenCV_DIR /usr/local/lib/cmake/opencv4) # set to system installation directory
+set(OpenCV_DIR ~/installation/opencv-4.1.2/build) # set to opencv build directory
+FIND_PACKAGE(OpenCV REQUIRED)
+```
+
+Another method: [cmake find_package specify path](https://stackoverflow.com/questions/49816206/cmake-find-package-specify-path)
+
+## ccmake
+Its usage: [A ccmake walk-through for the impatients](https://graal.ens-lyon.fr/diet/UsersManualDIET2.4/node22.html).
+
+## Conventions
+[Separating class code into a header and cpp file](https://stackoverflow.com/questions/9579930/separating-class-code-into-a-header-and-cpp-file)
+
+## Macros
+### #define, #if, #elif, #else, #end
+[Preprocessor check if multiple defines are not defined](https://stackoverflow.com/questions/17237545/preprocessor-check-if-multiple-defines-are-not-defined)
+```cpp
+#define <MACRO_A>
+
+#ifdef <MACRO_A>
+#elif defined(<MACRO_B>)
+#elif !define(<MACRO_C>) && !define(<MACRO_D>)
+#elif !define(<MACRO_E>) || !define(<MACRO_F>)
+#else
+#end
+```
+
+### include guard
+Naming convention for include guard: [How to properly name include guards in c++ [closed]](https://stackoverflow.com/questions/49688518/how-to-properly-name-include-guards-in-c)
+
+```
+For a file named "baz.h" in a project named "foo", in submodule "bar", I'd name the guard FOO_BAR_BAZ_H.
+```
+
+### #pragma once
+```cpp
+#ifndef __SOMEFILE_H__
+#define __SOMEFILE_H__
+// ...
+#endif
+```
+can be replaced with:
+```cpp
+#pragma once
+// ...
+```
+
+## mimic of python if __name__ == '__main__':
+
+In Python, say we have `foo.py` and `bar.py`, and they both have `if __name__ == '__main__':`(we can think this as `main` function in C++). We can easily `import foo` from `bar.py` or `import bar` from `foo.py` without any problem.
+
+But in C++, if `foo.cpp` and `bar.cpp` both have `main` fucntion, then when they are compiled together(`g++ foo.cpp bar.cpp`), there will be the linker error:
+
+```
+multiple definition of `main'
+```
+
+Indicating that there are multiple functions named `main` are being linked together. 
+
+So how to only enable one `main` function when compiling multiple `.cpp` files together? 
+
+Following is a workaround:
+
+In `foo.cpp`:
+
+```cpp
+#include "foo.h"
+#include "bar.h"
+
+int foo(){
+    return 0;
+}
+
+#ifdef FOO
+int main(){
+    return 0;
+};
+#endif
+```
+
+And in `bar.cpp`:
+
+```cpp
+int bar(){
+    return 0;
+}
+
+#ifdef BAR
+int main(){
+    return 0;
+};
+#endif
+```
+
+Wrap their `main` function with the macro `ifdef-endif`, and when compiling them, use:
+
+```sh
+g++ -DFOO foo.cpp bar.cpp
+```
+
+to only activate `foo.cpp`'s `main` function!