echo $0

prompt:~$ echo $0
/bin/bash
prompt:~$ sh
sh-4.0$ echo $0
sh
sh-4.0$ exit
exit
prompt:~$ /bin/sh
sh-4.0$ echo $0
/bin/sh
sh-4.0$

{
  "ret": "101",
  "error": [
    {
      "errortype": "A0001",
      "errorstroke": {
        "0": "0.2",
        "1": "0.3"
      }
    },
    {
      "errortype": "A0021",
      "errorstroke": {
        "0": "0.2",
        "1": "0.3"
      }
    }
  ]
}

#include <iostream>
#include <vector>
#include <string>

#include "rapidjson/document.h"
#include "rapidjson/writer.h"
#include "rapidjson/stringbuffer.h"

using namespace rapidjson;
using namespace std;

int main() {

    string ret =
            "{\"ret\":\"101\",\"error\":[{\"errortype\":\"A0001\",\"errorstroke\":{\"0\":\"0.2\",\"1\":\"0.3\"}},{\"errortype\":\"A0021\",\"errorstroke\":{\"0\":\"0.2\",\"1\":\"0.3\"}}]}";
    rapidjson::Document doc;
    doc.Parse<kParseDefaultFlags>(ret.c_str());
    if (doc.HasMember("ret")) {
        string retjson = doc["ret"].GetString();
        for (unsigned i = 0; i < retjson.length(); ++i) {
            cout << retjson.at(i) << " ";
        }
    }
    cout << endl;
    if (doc.HasMember("error")) {
        const Value & errorjson = doc["error"];
        for (SizeType i = 0; i < errorjson.Size(); ++i) {
            // 或者这里可以换用一种遍历使用 Value::ConstValueIterator
            // http://rapidjson.org/md_doc_tutorial.html#QueryArray
            if (errorjson[i].HasMember("errortype")) {
                string errortype = errorjson[i]["errortype"].GetString();
                cout << "errortype: " << errortype << endl;
            }
            if (errorjson[i].HasMember("errorstroke")) {
                const Value & errorstroke = errorjson[i]["errorstroke"];
                cout << "errorstroke" << endl;
                for (Value::ConstMemberIterator iter = errorstroke.MemberBegin();iter != errorstroke.MemberEnd(); ++iter) {
                    cout << iter->name.GetString() << ": " << iter->value.GetString() << endl;
                }
            }
        }
    }

    return 0;
}

/*
 first config your project to include /usr/local/include
 second link lib /usr/local/lib
 */

#include <iostream>
#include <boost/property_tree/ptree.hpp>
#include <boost/property_tree/json_parser.hpp>
#include <boost/foreach.hpp>
#include <string>

using namespace boost::property_tree;

int main(int argc, const char * argv[]) {

    std::string str_json = "{\"ret\":\"101\",\"error\":[{\"errortype\":\"A0001\",\"errorstroke\":{\"0\":\"0.2\",\"1\":\"0.3\"}},{\"errortype\":\"A0021\",\"errorstroke\":{\"0\":\"0.2\",\"1\":\"0.3\"}}]}";

    ptree pt;                       //define property_tree object
    std::stringstream ss(str_json);
    try {
        read_json(ss, pt);          //parse json
    } catch (ptree_error & e) {
        return 1;
    }

    std::cout << pt.get<std::string>("ret") << std::endl;
    ptree errortype = pt.get_child("error");            // get_child to get errors

    // first way
    for (boost::property_tree::ptree::iterator it = errortype.begin(); it != errortype.end(); ++it) {
        std::cout << it->first;
        std::cout << it->second.get<std::string>("errortype") << std::endl;
        ptree errorstroke = it->second.get_child("errorstroke");
        for (ptree::iterator iter = errorstroke.begin(); iter != errorstroke.end(); ++iter) {
            std::string key = iter->first;
            std::cout << iter->first << std::endl;
            std::cout << iter->second.data() << std::endl;
        }
    }

    // second way: using boost foreach feature
//    BOOST_FOREACH(ptree::value_type &v, errortype){
//        ptree& childparse = v.second;
//        std::cout << childparse.get<std::string>("errortype") << std::endl;
//        ptree errorstroke = childparse.get_child("errorstroke");
//        BOOST_FOREACH(ptree::value_type& w, errorstroke){
//            std::cout << w.first << std::endl;
//            std::cout << w.second.data() << std::endl;
//        }
//    }

    /*
     101
     A0001
     0
     0.2
     1
     0.3
     A0021
     0
     0.2
     1
     0.3
     */

    return 0;
}

for i = 2:n,
    for (k = i; k > 1 and a[k] < a[k-1]; k--)
        swap a[k,k-1]
    → invariant: a[1..i] is sorted
end

static void insert_sort(int[] array) {
    for(int i = 1; i < array.length; ++i) {
        int cur = array[i];
        for(int j = i - 1; j >= 0 && array[j] > cur; j--) {
            array[j + 1] = array[j];
            array[j] = cur;
        }
    }
}

list = [4,6,2,5,1,3,0,4,8,1,5,3,6]

# 升序
# 从第二个元素开始，每次循环将前 i 个元素排序
for i in range(1,len(list)):
    value = list[i]
    j = i-1
    # 将第 i 个元素的位置腾出
    while j >= 0 and list[j]>value:
        list[j+1] = list[j]
        j=j-1
    # 在排完序的 list[0...i] 中将值插入合适位置
    list[j+1]=value

# 降序
list = [4,6,2,5,1,3,0,4,8,1,5,3,6]

for i in range(len(list)-1, -1, -1):
    value = list[i]
    j=i+1
    while j<len(list) and value < list[j]:
        list[j-1] = list[j]
        j=j+1
    list[j-1]=value

print(list)

for i = 1:n,
    k = i
    for j = i+1:n, if a[j] < a[k], k = j
    → invariant: a[k] smallest of a[i..n]
    swap a[i,k]
    → invariant: a[1..i] in final position
end

list = [4,6,2,5,1,3,0,4,8,1,5,3,6]

for i in range(0,len(list)):
    k = i
    for k in range(i+1, len(list)):
    # 没有完全按照定义写，不过这样交换的开销更大。
        if list[k] < list[i]:
            list[i], list[k] = list[k], list[i]

print(list)

static void selection_sort(int[] array) {
	if(array.length <= 1) return;
	for(int i = 0; i < array.length; i++) {
		int smallest = i;
		for(int j = i + 1; j < array.length; j++) {
			if (array[j] < array[smallest]) {
				smallest = j;
			}
		}
		int temp = array[i];
		array[i] = array[smallest];
		array[smallest] = temp;
	}
}

for i = 1:n,
    swapped = false
    for j = n:i+1,
        if a[j] < a[j-1],
            swap a[j,j-1]
            swapped = true
    → invariant: a[1..i] in final position
    break if not swapped
end

def bubble_sort_1(list):
    for i in range(0, len(list)):
        for j in range(1, len(list)-i):
            if list[j-1] > list[j]:
                list[j-1], list[j] = list[j], list[j-1]

def bubble_sort_2(list):
    for i in range(0, len(list)):
        swap = False
        for j in range(len(list)-1, i, -1):
            if list[j-1] > list[j]:
                list[j-1], list[j] = list[j], list[j-1]
                swap = True
        if swap is False:
            break

static void bubble_sort(int[] arr) {
	int i, j, temp, len = arr.length;
	for (i = 0; i < len - 1; i++)
		for (j = 0; j < len - 1 - i; j++)
			if (arr[j] > arr[j + 1]) {
				temp = arr[j];
				arr[j] = arr[j + 1];
				arr[j + 1] = temp;
			}
}

h = 1
while h < n, h = 3*h + 1
while h > 0,
    h = h / 3
    for k = 1:h, insertion sort a[k:h:n]
    → invariant: each h-sub-array is sorted
end

list = [4,6,2,5,1,3,0,4,8,1,5,3,6]

def insertion_sort(k,h,n):
    """
    :param k: group count
    :param h: step length
    :param n: total
    :return:
    """
    for i in range(k+h, n, h):
        value = list[i]
        j = i-h
        while j >= 0 and list[j]>value:
            list[j+h] = list[j]
            j=j-h
        list[j+h]=value


h = 1       # step length
while h < len(list):
    h = 3*h +1

while h > 0:
    h = int(h / 3)
    for k in range(0, h):           # devide into k groups
        insertion_sort(k, h, len(list))

print(list)

# split in half
m = n / 2

# recursive sorts
sort a[1..m]
sort a[m+1..n]

# merge sorted sub-arrays using temp array
b = copy of a[1..m]
i = 1, j = m+1, k = 1
while i <= m and j <= n,
    a[k++] = (a[j] < b[i]) ? a[j++] : b[i++]
    → invariant: a[1..k] in final position
while i <= m,
    a[k++] = b[i++]
    → invariant: a[1..k] in final position

from collections import deque

def merge_sort(lst):
    if len(lst) <= 1:
        return lst

    def merge(left, right):
        merged,left,right = deque(),deque(left),deque(right)
        while left and right:
            merged.append(left.popleft() if left[0] <= right[0] else right.popleft())  # deque popleft is also O(1)
        merged.extend(right if right else left)
        return list(merged)

    middle = int(len(lst) // 2)
    left = merge_sort(lst[:middle])
    right = merge_sort(lst[middle:])
    return merge(left, right)

# heapify
for i = n/2:1, sink(a,i,n)
→ invariant: a[1,n] in heap order

# sortdown
for i = 1:n,
    swap a[1,n-i+1]
    sink(a,1,n-i)
    → invariant: a[n-i+1,n] in final position
end

# sink from i in a[1..n]
function sink(a,i,n):
    # {lc,rc,mc} = {left,right,max} child index
    lc = 2*i
    if lc > n, return # no children
    rc = lc + 1
    mc = (rc > n) ? lc : (a[lc] > a[rc]) ? lc : rc
    if a[i] >= a[mc], return # heap ordered
    swap a[i,mc]
    sink(a,mc,n)

def max_heapify(lst, i):
    """
    下标为 i 的根节点调整为最大堆
    :param lst:
    :param i:
    :return:
    """
    l = 2 * i + 1
    r = 2 * (i + 1)
    if l < len(lst) and lst[l] > lst[i]:
        largest = l
    else:
        largest = i
    if r < len(lst) and lst[r] > lst[largest]:
        largest = r
    if largest != i:
        lst[i], lst[largest] = lst[largest], lst[i]
        max_heapify(lst, largest)


def build_max_heap(lst):
	"""
    建立最大堆
    """
    for i in range((len(lst)-1)/2, 0, -1):
        max_heapify(lst, i)


def heap_sort(lst):
    build_max_heap(lst)
    ret = []
    for i in range(len(lst)-1, -1, -1):
        ret.append(lst[0])
        lst.remove(lst[0])
        max_heapify(lst, 0)
    return ret

L = [16, 4, 10, 14, 7, 9, 3, 2, 8, 1]
R = heap_sort(L)
print(R)

# choose pivot
swap a[1,rand(1,n)]

# 2-way partition
k = 1
for i = 2:n, if a[i] < a[1], swap a[++k,i]
swap a[1,k]
→ invariant: a[1..k-1] < a[k] <= a[k+1..n]

# recursive sorts
sort a[1..k-1]
sort a[k+1,n]

list_demo = [2,8,7,1,3,5,6,4]

def partition(lst, p, r):
    """
    划分
    :param lst: 待排序数组
    :param p: 起始下标，子数组第一个元素
    :param r: 终止下标，子数组最后一个元素 r < len(lst)
    :return: 划分结果下标
    """
    if r >= len(lst) or p < 0:
        return
    x = lst[r]
    i = p - 1
    for j in range(p, r):
        if lst[j] <= x:
            i += 1
            lst[i], lst[j] = lst[j], lst[i]
    lst[i+1], lst[r] = lst[r], lst[i+1]
    return i + 1


def quick_sort(lst, p, r):
    if p < r:
        q = partition(lst, p, r)
        quick_sort(lst, p, q-1)
        quick_sort(lst, q+1, r)

quick_sort(list_demo, 0, len(list_demo)-1)
print(list_demo)

sudo apt install dnsutils

   nslookup [-option] [name | -] [server]

nslookup
> www.douban.com
Server:	127.0.1.1   // 连接的 DNS 服务器
Address:	127.0.1.1#53    // DNS 服务器 IP 地址与端口

Non-authoritative answer:    // 非权威答案，从连接的 DNS 服务器本地缓存中读取，非实际查询得到
Name:	www.douban.com
Address: 115.182.201.6    // IP 地址
Name:	www.douban.com
Address: 115.182.201.7
Name:	www.douban.com
Address: 115.182.201.8

nslookup www.douban.com [dns-server]

#include <iostream>  
using namespace std;  

class A  
{  
public:  
    void foo()  
    {  
        printf("1\n");  
    }  
    virtual void fun()  
    {  
        printf("2\n");  
    }  
};  
class B : public A  
{  
public:  
    void foo()  
    {  
        printf("3\n");  
    }  
    void fun()  
    {  
        printf("4\n");  
    }  
};  
int main(void)  
{  
    A a;  
    B b;  
    A *p = &a;  
    p->foo();  
    p->fun();  
    p = &b;  
    p->foo();  
    p->fun();  
    return 0;  
}  

B *ptr = (B *)&a;  ptr->foo();  ptr->fun();

friend <类型><友元函数名>(<参数表>);  

#include <iostream>
using namespace std;

class Base{
public:
    Base(int _data):data(_data){};

    friend int getData(Base& _base);
private:
    int data;
};

int getData(Base& _base){
    return _base.data;
}

int main() {
    Base b(2);
    std::cout << getData(b) << endl;
    return 0;
}

friend class <友元类名>;

#include <iostream>
using namespace std;

class Base{
public:
    Base(int _data):data(_data){};

    friend class FClass;
private:
    int data;
};

class FClass{
public:
    int getData(Base _base){
        return _base.data;		// call friend class private data
    }
};

int main() {
    Base b(2);
    FClass c;
    cout << c.getData(b) << endl;
    return 0;
}

#include <iostream>

void f0(int& sum){
    sum = 3+2*7;
}

int main() {
    int *p, sum = 0;
    (*p)++;
    sum = sum * 3;
    f0(sum);
    std::cout << sum << ",";
    return 0;
}

uname -r

dpkg -l | grep linux-image

sudo apt search linux-image
sudo apt install xxx
sudo apt-get purge xxx

sudo apt-get install dkms

dkms status