YAML-CPP

yaml作为一种便捷的文件格式，通过c++进行操作时，可以利用yaml-cpp进行。

一，yaml-cpp的安装

下载源码

git clone https://github.com/jbeder/yaml-cpp.git

编译安装

mkdir build
cd build
cmake -DBUILD_SHARED_LIBS=ON ..    # ON 设置生成共享库
sudo make install

验证

pkg-config --modversion yaml-cpp

使用

YAML::Node node1 = YAML::LoadFile("config.yaml");    // 加载文件
YAML::Node node2 = YAML::Load("[1,2,3]");        // 加载数组
cout << node1[0].as<string>() << endl;
cout << node2[0].as<int>() << endl;        // 输出元素

更多API参考yaml-cpp docs。

示例：

a、CMakeLists.txt

cmake_minimum_required(VERSION 2.8)
project(yaml_test)
set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11")
link_directories(/home/jonty/Softwares/yaml-cpp/build)
include_directories(/home/jonty/Softwares/yaml-cpp/include/yaml-cpp)
add_executable(test main.cpp)
target_link_libraries(test yaml-cpp)

b、main.cpp

#include <iostream>
#include "yaml.h"
using namespace std;
int main()
{
    YAML::Node node = YAML::Load("[22,3,4,4]");
    cout << node[0] << endl;
    YAML::Node node2 = YAML::LoadFile("../config.yaml");
    cout << node2["ttt"] << endl;
    return 0;
}

编译运行

mkdir build
cd build
cmake ..
make
./test

参考教程https://github.com/jbeder/yaml-cpp/wiki/Tutorial

编译也可以采用g++ test.cpp /usr/local/lib/libyaml-cpp.a -std=c++11

源码编译yaml-cpp

git clone https://github.com/jbeder/yaml-cpp.git

cd yaml-cpp # 进入克隆的文件夹
mkdir build
cd build
cmake ..
make
make install

可参考https://blog.csdn.net/Fourier_Legend/article/details/82798297

记得在CMakeLists.txt中加入

link_directories(/usr/local/lib)
include_directories(/usr/local/include/yaml-cpp)

以及在链接库target_link_libraries时，加上yaml-cpp。

void write_robot_status_to_yaml(string path, const string &filename,
                                double x, double y, double th)
{
    //dir_file_exists(path, true);
    dir_file_exists(path, false, true, filename.c_str());
    std::ofstream yaml_file(path + filename, std::ios::out | std::ios::binary);
    {
        YAML::Emitter out(yaml_file);
        out << YAML::BeginMap;
        // TODO(whess): Use basename only?
        out << YAML::Key << "x";
        out << YAML::Value << x;
        out << YAML::Key << "y";
        out << YAML::Value << y;
        out << YAML::Key << "th";
        out << YAML::Value << th;
        out << YAML::EndMap;
    }

    yaml_file.close();
}

bool read_robot_status_from_yaml(string file_path, const string &file_name,  double &x,
                                 double &y, double &th)
{
    if (!dir_file_exists(file_path, false, true, file_name.c_str()))
        return false;
    std::ifstream yaml_file(file_path + file_name, std::ios::out | std::ios::binary);
    {
        YAML::Node doc = YAML::Load(yaml_file);

        doc["x"] >> x;
        doc["y"] >> y;
        doc["th"] >> th;
    }
    yaml_file.close();

    return true;
}

/*
 * @brief 创建文件夹
 */
bool dir_file_exists(string dir, bool mkdir_flag, bool touchfile_flag, string filename)
{
    char des_dir[];
    str_2_char(dir, des_dir);
    int state = access(des_dir, R_OK | W_OK);//#include<unistd.h>
    if(state == )
    {
        ROS_INFO("state == 0");
        return true;
    }
    else if(mkdir_flag)
    {
        dir = "mkdir " + dir;
        str_2_char(dir, des_dir);
        if(system(des_dir))
        {
            printf("generate dir %s successfully.",dir.c_str());
            ROS_INFO("generate dir %s successfully.",dir.c_str());
            //Basic_Info("generate dir {} successfully.",dir.c_str());
        }
        else
        {
            printf("generate dir %s fail.",dir.c_str());
            ROS_INFO("generate dir %s fail.",dir.c_str());
            //Basic_Info("generate dir {} fail.",dir.c_str());
        }
        return true;
    }
    else if(touchfile_flag)
    {
        dir = "touch " + dir + "/" + filename;
        ROS_INFO("dir is %s", dir.c_str());
        str_2_char(dir, des_dir);
        if(system(des_dir))
        {
            printf("generate filename %s successfully.",dir.c_str());
            ROS_INFO("generate filename %s successfully.",dir.c_str());
            //Basic_Info("generate filename {} successfully.",dir.c_str());
        }
        else
        {
            printf("generate filename %s fail.",dir.c_str());
            ROS_INFO("generate filename %s fail.",dir.c_str());
            //Basic_Info("generate filename {} fail.",dir.c_str());
        }
        return true;
    }
        return false;
}

template <typename T>
void operator>>(const YAML::Node& node, T& i);

template <typename T>
void operator>>(const YAML::Node& node, T& i) {
    i = node.as<T>();
};

写个模板类加载参数

template<typename T>
T getParam(const string& name,const T& defaultValue)　　//This name must be namespace+parameter_name
{
    T v;
    if(ros::param::get(name,v))　　//get parameter by name depend on ROS.
    {
        ROS_INFO_STREAM("Found parameter: "<<name<<",\tvalue: "<<v);
        return v;
    }
    else
        ROS_WARN_STREAM("Cannot find value for parameter: "<<name<<",\tassigning default: "<<defaultValue);
    return defaultValue;　　//if the parameter haven't been set,it's value will return defaultValue.
}

在ROS系统中，参数读写一般通过xml或者yaml格式的文件，其中yaml用得比较多。这是一种可读性高，轻量级的标记语言，简单好用。
对于yaml文件，ros中用的较早版本的yaml-cpp库，最新的可在github上下载，并按照readme中所述的方法编译安装。

特别留意的是，如果需要生成共享库，cmake的时候后面一定要加上 -DBUILD_SHARED_LIBS=ON 这句话。

有了yaml库，在CMakeLists.txt中加入，

link_directories(/usr/local/lib)
include_directories(/usr/local/include/yaml-cpp)

最后别忘了在链接库target_link_libraries时，加上yaml-cpp。
关于库的使用，github上有一些简单的tutorial教程。

以下是简单的yaml文件读写操作示例。

#include <ros/ros.h>
#include <yaml-cpp/yaml.h>
#include <iostream>
#include <fstream>

int main(int argc, char **argv)
{
    std::string fin = "/home/user/param/param.yaml";       //yaml文件所在的路径
    YAML::Node yamlConfig = YAML::LoadFile(fin);
    int int_param = yamlConfig["int_param"].as<int>();
    std::cout << "  node size: " << yamlConfig.size() << std::endl;
    std::cout << yamlConfig["bool_param"].as<bool>() << "\n";
    yamlConfig["bool_param"] = !yamlConfig["bool_param"].as<bool>();
    yamlConfig["str_param"] = "test";
    std::ofstream file;
    file.open(fin);
    file.flush();
    file << yamlConfig;
    file.close();

    return ;
}

其中，yaml文件里的内容为：

bool_param: true
int_param: 2
double_param: 0.5
str_param: "123"

也可采用Emit来生成yaml文件，代码如下：

#include <ros/ros.h>
#include <yaml-cpp/yaml.h>
#include <iostream>
#include <fstream>

int main(int argc, char **argv)
{
    std::ofstream fout("/home/user/param/param.yaml");
    YAML::Emitter out(fout);
    out << YAML::BeginMap;
    out << YAML::Key << "int_param";
    out << YAML::Value << ;
    out << YAML::Key << "double_param";
    out << YAML::Value << 0.5;
    out << YAML::Key << "bool_param";
    out << YAML::Value << false;
    out << YAML::Comment("bool parameter");
    out << YAML::Key << "str_param";
    out << YAML::Value << "test";
    out << YAML::EndMap;

    return ;
}

yml文件的其他操作可参见博文《.yaml参数文件的编写和使用》，

其综合运用的案例可参见博文：ros-opencv-qt-yaml综合运用之滤波。