3.3 自增/自减操作符,和Side effects
from http://www.learncpp.com/cpp-tutorial/33-incrementdecrement-operators-and-side-effects/
一个变量自增1与自减1是如此的平常,以至于在C中它们有了自己的操作符。每一个操作符都有两个版本——前缀与后缀。
Operator | Symbol | Form | Operation |
---|---|---|---|
Prefix increment | ++ | ++x | Increment x, then evaluate x |
Prefix decrement | –– | ––x | Decrement x, then evaluate x |
Postfix increment | ++ | x++ | Evaluate x, then increment x |
Postfix decrement | –– | x–– | Evaluate x, then decrement x |
如:
1: int x = 5;
2: int y = ++x; // x is now equal to 6, and 6 is assigned to y
1: int x = 5;
2: int y = x++; // x is now equal to 6, and 5 is assigned to y
再举一例来显示前置与后置之间的差别:
1: int x = 5, y = 5;
2: cout << x << " " << y << endl;
3: cout << ++x << " " << --y << endl; // prefix
4: cout << x << " " << y << endl;
5: cout << x++ << " " << y-- << endl; // postfix
6: cout << x << " " << y << endl;
结果为:
5 5 6 4 6 4 6 4 7 3
Side effects
A side effect is a result of an operator, expression, statement, or function that presists even after the operator, expression, statement, or function has finished being evaluated.
(能不能解释为,表达式,函数,或语句等求值以后的结果)
如:
1: x = 5;
是有用的。
而:
1: int x = 5;
2: int nValue = Add(x, ++x);
C++并没有定义函数中哪个参数先被求值。可能产生两种结果:1、Add(5,6) 2、Add(6,6).
一个通用的规则是避免使用会引起类似结果的操作符。所有的赋值操作符、自增自减。会引起side effect的操作符因该放在独立的语句中。
有谁能解释一下side effects不??
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