enum

2017-05-13 yuiwongCPP

c++ 11 and above enum

grammar

enum [identifier] [: type] {
  ...,
  ...,
};

example

namespace costmap_2d {
/**
 * @brief TALL_OBSTACLE for 3d nav
 */
enum: unsigned char {
    TALL_OBSTACLE = 252,
};
}

example 2

enum class A {
    A = 3,
    B = 10,
};

A somea = A::A;

see also

how to cpp (coding)

2017-04-222017-04-22 yuiwongCPP

how to cpp (coding)

my cpp standard (style / specification / .. how to coding!)

#

first level list
further

list

simple thing should be simple

no redundant prefix, e.x. m / _ / i / ..
no redundant suffix, e.x. _ / ..
example not:

bool bShouldReboot;
int iNumber;
AAAA maaaa;
BBBB bbbb_;


/* then access example */
if (bShouldReboot) { /* where the bShouldReboot from */
}
bbbb_.foo(); /* where the bbbb_ from */

but should be:

bool shouldReboot;
int number;
AAAA aaaa;
BBBB bbbb;

/* then access example */
if (self.shouldReboot) { /* the shouldReboot is myself */
}

if (this->shouldReboot) {
}

this->bbbb.foo(); /* the bbbb from this object */

about ostream

better not use endl .. std::endl, but \n is ok !

indent

usually 1 is enough!!

example not

void somemaybeokfooMaybebadaaa(const AAAA& aaaa, const BBBB& bbbb,
                               const CCCC& cccc, const DDDD& dddd,
                               const EEEE& eeee);

but should be

void somemaybeokfooMaybebadaaa(
    const AAAA& aaaa,
    const BBBB& bbbb,
    const CCCC& cccc,
    const DDDD& dddd,
    const EEEE& eeee);

80

yes !! usually max width of each line is 80
可以换行啊 !!!

no garbage

no garbage lines at middle of file
no garbage lines at end of file
no garbage space (space / table / ..) at end of line
no garbage space (space / table / ..) at begin of line(
example, need 2 but 3 provided)

1 space

example not:

if(some){
}

sum=a+b;

but shoule be

if (some) {
}

sum = a + b;

block statement

always {}, even if 1 statement, example:

/* NOT */
some;
if (ok)
    fly();
else
    walk();
other;

/* BUT SHOULE BE: */
some;
if (ok) {
    fly();
} else {
    walk();
}
other;

/* and further more is good: */
some;
if (ok) {
    fly();
    saysomething();
} else {
    walk();
}
stopFirst();
other;

path

example for include: NOT ../../.hpp or ../.hpp
or too/many/name/...hpp

but should be: some/…hpp and use -I...

lower and upper

type: Type
instance / member: instance / data / foo / staticFoo
generic function: Foo

prefix

better no! if could be simple !!
global: use k e.x. kGraphProcessor.
(NOT use e.x. g)

plusplus

if not have to be some++(case for some++ when which can simplify 2 to 1)

SO USUALLY use ++some (not use some++ if not have to), because:
i see plus one, the result of the expression should be plused one !!
but this expression maybe little silly!

example, better:

for (size_t i = 0; i < sz; ++i) {
}

/* got whatsthis */
++whatsthis;/* should plus one or whatsthis += 1; */
someFoo(whatsthis);

when to declare

when to declare: when use, example

/* BAD: heyheyhey example */
Some heyheyhey;/* BAD */
doSome();
doOther();
thisFooNeedRefAndAlwaysSetIt(heyheyhey);

/* BAD: heyheyhey example 2 */
Some heyheyhey = 0;/* BAD */
...
thisFooNeedRefAndMaybeNotSetIt(heyheyhey);

/* BAD: heyheyhey example 3 */
Some heyheyhey;/* BAD */
heyheyhey = 0;/* BAD */
...
thisFooNeedRefAndMaybeNotSetIt(heyheyhey);

/* BAD: heyheyhey example 4 */
Some heyheyhey;/* BAD */
doSome();
...
heyheyhey = 0;/* BAD */
thisFooNeedRefAndMaybeNotSetIt(heyheyhey);

/* GOOD: heyheyhey example */
doSome();
doOther();
Some heyheyhey;/* GOOD ! */
thisFooNeedRefAndAlwaysSetIt(heyheyhey);

/* GOOD: heyheyhey example 2 */
doSome();
...
Some heyheyhey = 0;/* GOOD ! */
thisFooNeedRefAndMaybeNotSetIt(heyheyhey);

how to assign init

how to assign: do not assign repeatedly or maybe repeatedly, example

/* bad: */
size_t count = 10;
if (ok) {
    count  = 100;
}

/* good: */
size_t count;
if (ok) {
    count  = 100;
} else {
    count  = 10;
}

should dump when need

for data thread safe
for less call: if use not only once => dump it!, example

/*
 * consider now datas is latched .. here means
 * bad case:
 */
some();
for (size_t i = 0; i < datas.size(); ++i) {
    foo(datas[i]);
}
other();

/*
 * bad case 2:
 */
sayToSomebody(getNameById(1), "hi");
sayToSomebody(getNameById(1), "hey");

/*
 * consider now datas is latched .. here means
 * good case:
 */
some();
{
    const size_t sz = datas.size();/* dump the size */
    for (size_t i = 0; i < sz; ++i) {
        foo(datas[i]);
    }
}
other();

/*
 * good case 2:
 */
{
    const std::string who = getNameById(1);/* dump the name */
    sayToSomebody(who, "hi");
    sayToSomebody(who, "hey");
}

how to debug by output log

__FILE__
__LINE__

/* SO BAD example */
some();
std::cout << "aaaaa" << std::endl;
watch();
std::cout << "bbbbb222222!!!" << std::endl;/* what u b !! */

/* GOOD example */
some();
std::cout << "(" << __FILE__ << "+" << __LINE__ << ")" NAME " "
    << "before watch\n";/* good */
watch();
std::cout << "(" << __FILE__ << "+" << __LINE__ << ")" NAME " "
    << "after watch\n";/* good */

/* further more */
const int err = fly();
if (err) {
    std::cerr << "(" << __FILE__ << "+" << __LINE__ << ")" NAME " "
        << "ERROR: fly fail: " << err << "\n";/* so good */
    die();
}

no flag

just better NOT use the name flag, example:

/* bad case */
void setStartable(bool flag)
{
    this->startable = flag;
}

/* bad case 2 */
void setResult(bool flag)
{
    this->startable = flag;
}

/* good case: just to what it should be */
void setStartable(bool startable)
{
    this->startable = startable;
}

/* good case 2 */
void setResult(bool result)
{
    this->result = result;
}

further

c++

2017-03-05 yuiwongCPP

my c++ .. yuiwong.org .. c++

my (yuiwong.org) c++ basics 02
previous see https://yuiwong.org/2016/11/16/cpp/

#

tips
see also

tips

c++ !!!

封装
继承
polymorphism 多态

polymorphism 多态

多态: 是对于不同对象接收相同消息时产生不同的动作.
c++ 的多态性具体体现在运行和编译两个方面:
- 在程序运行时的多态性通过继承和虚函数来体现
- 在程序编译时多态性体现在函数和运算符的重载上
c impl. 封装: struct
c impl. 继承: container_of
- see https://yuiwong.org/gitweb/?p=posix.git;a=tree

/**
 * @brief YUIWONGORGPOSIX_CONTAINER_OF / YUIWONGORGPOSIX_DOWNCAST (container_of) (c)
 * @description 结构体: 通过成员地址找到首地址 / downcast parent to sub
 * @param
 * - `type':
 *   首地址 - 类型
 *   Or. downcast - "subtype" "子类"类型
 * - `memptr'
 *   首地址 - 成员地址
 *   Or. donwcast - parptr: 子类的"父类"成员(组合)的地址
 * - `mem'
 *   首地址 - mem 成员名
 *   Or. downcast - "父类作为子类的成员"(组合)的名字
 */
#define YUIWONGORGPOSIX_CONTAINER_OF(type, memptr, mem) \
    ((type *)((unsigned long)(memptr) \
    - (unsigned long)&((type *)0)->mem))
#define YUIWONGORGPOSIX_DOWNCAST YUIWONGORGPOSIX_CONTAINER_OF

c impl. 多态: 函数指针

sort

冒泡排序
快速排序
选择排序

see TODO

size

size of empty class: 1
size of empty struct: 1
note: sizeof(double): 8
sizeof addr type <=> size of size type
sizeof win x86_64 long: 4 but addr type is 8. other same to addr type
see https://yuiwong.org/gitweball/?p=cpp-basics.git;a=tree

misc

stl std::map 实现: 红黑树
stl std::vector 调整大小
iterator / iterator 模式
- 提供一种方法顺序访问一个聚合对象中各个元素而又不需暴露该对象的内部表示
- see https://yuiwong.org/gitweball/?p=cpp-basics.git;a=tree
- iterators
template TODO
typename and classname TODO
typedef TODO
typealias TODO
空值类型: void
sometype *restrict someptr — restrict:

所有修改该指针所指向内存中内容的操作都必须通过该指针或者直接来自该指针的值
(例如 pointer + 1)

* gcc clang .. c++: `__restrict__`
* vc++ .. c++: `__restrict` and `__declspec(restrict)`
* c99 `memcpy`:
`void * memcpy(void *restrict dest, const void *restrict src, size_t n);`
`restrict` => let `memcpy()` 可以假定两个内存区域没有重叠.
=> 使用 `memcpy()` 时, 您必须确保没有重叠区域. 这是程序员的任务的一部分.
* see <https://yuiwong.org/gitweball/?p=cpp-basics.git;a=tree>

memcpy and memmove
- memcpy: 不能重叠
- memmove: 先复制到临时缓冲
- see https://yuiwong.org/gitweball/?p=cpp-basics.git;a=tree
__attribute__(GNU), __declspec(ms) and #pragma: 编译器工具到语言的扩展
- Attributes 属性
  C++11 provides a standardized syntax for compiler/tool extensions
  to the language.
  Such extensions were traditionally specified using #pragma directive
  or vendor-specific keywords (like __attribute__ for GNU
  and __declspec for Microsoft).
- see https://yuiwong.org/gitweball/?p=cpp-basics.git;a=tree
explicit (显式)
- explicit 是避免构造函数的参数自动转换为类对象的标识符
  => 必须要显示地调用构造函数
  => 即类似看到效果: 避免了创建临时对象
  (实际并没有看到调用两次 ctor 而是避免了自动转换)
- see https://yuiwong.org/gitweball/?p=cpp-basics.git;a=tree
union TODO
assign operator: 注意: 需要判断是否是本身特别不是通过构造函数实现时
stream operator TODO
cast operator TODO
subscript 即 [] operator
- std::map: 没有 idx 下标操作, 有 key 下标操作
- std::list 无下标操作
- std::set 无下标操作
c++ struct 可以有构造函数、普通函数访问修饰继承等像 class 一样
static var 会初始化 (包括作用域内)

c++ advanced

智能指针
- see TODO
设计模式
- see TODO
虚函数虚函数表虚函数表地址 and 运行时多态 TODO
虚析构函数 TODO
子类析构父类析构 TODO
container TODO
collection TODO
stl c++11 and above multi-threading
- <atomic> atomic (header)
- <thread> thread (header)
- <mutex> mutex (header)
- <condition_variable> condition variable (header)
- <future> future (header)
- see TODO
optional, nullopt_t, nullopt TODO
nullptr_t, nullptr TODO
any TODO
var.. TODO
forward TODO

typeid (header <typeinfo>) 用于类型检查 => rtti

example

const std::type_info& ti1 = typeid(A);
const std::type_info& ti2 = typeid(A);
assert(&ti1 == &ti2); /* not guaranteed */
assert(ti1.hash_code() == ti2.hash_code()); /* guaranteed */
assert(std::type_index(ti1) == std::type_index(ti2)); /* guaranteed */

see TODO

cast
- 隐式转换
- 显式转换
- const_cast
- static_cast
- reinterpret_cast
- dynamic_cast
- cast_operator 转换操作符 (e.x. std::nullptr)
some more casts
- downcast: downcast parent to sub(child)
- upcast: upcast sub(child) to parent
- sidecase: cast to 兄弟类
- see TODO

M	T	W	T	F	S	S
					1	2
3	4	5	6	7	8	9
10	11	12	13	14	15	16
17	18	19	20	21	22	23
24	25	26	27	28	29	30
31

c++ 11 and above enum

how to cpp (coding)

list

simple thing should be simple

about ostream

indent

80

no garbage

1 space

block statement

path

lower and upper

prefix

plusplus

when to declare

how to assign init

should dump when need

how to debug by output log

no flag

further

my c++ .. yuiwong.org .. c++

tips

c++ !!!

polymorphism 多态

sort

size

misc

c++ advanced

see also