cpp-code-snippets

Some useful C++ code snippets

Compile

Compiling with g++

Compile, specify c++ version

to_string is not a member of std, says g++ (mingw)

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

g++ xxx.cpp -I /usr/local/include

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

set variable and print

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?

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?

CMAKE_SOURCE_DIR: the folder containing the top-level CMakeLists.txt

PROJECT_SOURCE_DIR: the inner-most folder containing CMakeLists.txt with project() command

make, specify number of jobs as the number of processing units available

make -j $(nproc)

cmake in debug mode and make in verbose mode

Using CMake with GNU Make: How can I see the exact commands?

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

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

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

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

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

LD_LIBRARY_PATH=/usr/local/lib ./a.out

or

export LD_LIBRARY_PATH=/usr/local/lib:$LD_LIBRARY_PATH

stack smashing detected

From StackOverflow - Stack smashing detected, 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)

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):

echo vm.swappiness=0 | sudo tee -a /etc/sysctl.conf

specify CUDA path while cmake

How to let cmake find CUDA

Method 1, use -D flag while cmake:

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

Conventions

Separating class code into a header and cpp file

Macros

#define, #if, #elif, #else, #end

Preprocessor check if multiple defines are not defined

#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

#pragma once

#ifndef __SOMEFILE_H__
#define __SOMEFILE_H__
// ...
#endif

can be replaced with:

#pragma once
// ...