[note] Effective C++ Chapter 1

Effective C++ Learning Note 1
(undergradute edition)

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View C++ as a Federal of PL

SubLanguage

C

• Blocks
• Statements
• preprocessor: kind of instructions. started with ‘#’
• built-in date types
• arrays(basic DS)
• pointers
• no templates, exceptions, and overloading

OO C++

classic practice of OOP

• classes
• encapsulation
• inheritance
• polymorphism
• dynamic binding(virtual function)

Template C++——generic programming

• templates
• TMP(Template metaprogramming, 模板元编程) seldom intefere each other

STL

• containers
• iterators
• algorithms
• functionals

different preferences

An example:

• in C-like and STL: pass-by-value
• in OOC or TC: pass-by-reference-to-const

sum-up

Effective rules vary in the sublanguages.

Prefer consts, enums, and inline to '#define’s

prefer compiler to preprocessor

from #defines to const

main reasons

preprocessor replace; compiler could repace(better tail-after, more visulization)

if not, the replaced ones are difficult to watch and debug. Especially when it’s in another file written not by myself.

two cases of const

• const pointer.

const char* const kBloggerName = "Honour-Van"

• in-class consts

class GamePlayer{
private:
    static const int NumTurns = 5; // only declaration
    int scores[NumTurns];          // using the const
}

On condition that we need to take address or compiler wrongly insisted, we need:

const int GamePlayer::NumTurns;

Tips: we seldom initialize vars in classess, except for consts
because we may declare several times, but only implement only once(during which we alloc the address to the vars.)

enum hack

if our attempt to initialize the const we stated above or use the static const to declare the array is FAILED(this is totally to blame for the foolish compiler), we can use the enum hack to compensate.

in the link on the runoob, enum hack is described as a seldom used technique.

advt:

• another kind of static const int var, without troubling CE.
• quite like #define(which means no unecessary memry alloc to it, thus, we cannot take its address), but has infinite scope.

Macro functions

macros look like functions but that don’t incur the overhead of a function call.

but macro functions often made things foobar.

an awful example:

// call f with the maximum of a and b
#define CALL_WITH_MAX(a, b) f((a) > (b) ? (a) : (b));
int a = 5, b = 0;
CALL_WITH_MAX(++a, b); // a is incremented twice
CALL_WITH_MAX(++a, b+10); // a is incremented once

possible BEST

using inline template functions

template<typename T>        // because we don't
inline void callWithMax(const T& a, const T& b)                         
                    // know what T is, we
{                   // pass by reference-to
f(a > b ? a : b); // const
}

Use const whenever possible

various usages in pointers

char greeting[] = "Hello";
char *p = greeting; // non-const pointer,non-const data
const char *p = greeting; // non-const pointer, const data
char * const p = greeting; // const pointer, non-const data
const char * const p = greeting; // const pointer, const data

the only key is the order of const and *,

• if the former is prior, it means that we cannot change the data by the pointer;
• else: we cannot point the pointer to another place.

but the order of const and data type doesn’t count:

void f1(const Widget *pw); // f1 takes a pointer to a constant Widget object
void f2(Widget const *pw); // so does f2

iterators:

iterator	pointer declr	figurative
const <T>::iterator it	T* const p	target
<T>::const_iterator cit	const T* p	camera

const functions

mainly when dealing with the user-type

pass-by-param

• value: unnecessary
• pointer: we have discussed before
• pass-by-reference: user-type necessary(to cut the cost of copying)

return type

• built-in type: unnecessary
• const user-type: cannot be used as lval
• const pointer or const reference: somtimes useful

members

often used as interface.
if we want to change a specific member in the const function, you’d use the mutable keyword

Initialization of Object(omitted)

• make sure local vars and user-class type vars be initialized.
• the constructing orders in the derived class.