3.4 sizeof, comma, and arithmetic if operators

from http://www.learncpp.com/cpp-tutorial/34-sizeof-comma-and-arithmetic-if-operators/

sizeof

Operator	Symbol	Form	Operation
Sizeof	sizeof	sizeof(type) sizeof(variable)	Returns size of type or variable in bytes

sizeof操作符返回以字节为单位的变量或是类型的大小。

如：

   1: #include <iostream>

   2:  

   3: int main()

   4: {

   5:     using namespace std;

   6:     cout << "bool:\t\t" << sizeof(bool) << " bytes" << endl;

   7:     cout << "char:\t\t" << sizeof(char) << " bytes" << endl;

   8:     cout << "wchar_t:\t" << sizeof(wchar_t) << " bytes" << endl;

   9:     cout << "short:\t\t" << sizeof(short) << " bytes" << endl;

  10:     cout << "int:\t\t" << sizeof(int) << " bytes" << endl;

  11:     cout << "long:\t\t" << sizeof(long) << " bytes" << endl;

  12:     cout << "float:\t\t" << sizeof(float) << " bytes" << endl;

  13:     cout << "double:\t\t" << sizeof(double) << " bytes" << endl;

  14:     cout << "long double:\t" << sizeof(long double) << " bytes" << endl;

  15:     return 0;

  16: }

 

 

comma

Operator	Symbol	Form	Operation
Comma	,	x, y	Evaluate x then y, return value of y

逗号操作符返回的是最右边的操作数。

   1: int x = 0;

   2: int y = 2;

   3: int z = (++x, ++y); // increment x and y

   4: cout << z << endl;

结果为

3

一般情况下不使用逗号操作符

 

Arithmetic if

Operator	Symbol	Form	Operation
Arithmetic if	?:	c ? x : y	If c is nonzero (true) then evaluate x, otherwise evaluate y

if (condition)

    x = some value

else

    x = some other value

等同于

x = (condition) ? some value : some other value;