问题描述
之间是否存在差异（int i = 0;某些条件; i ++）
{....}
和
for（int i = 0;某些条件; ++ i）？
{....}
似乎没有，通过一些实验，但我认为值得
检查因为j ++和++ j通常意味着不同的东西在
语言++ c。
非常感谢，
Paul Epstein
你的意思是......性能，语义，...的差异？？
从语义上看，存在差异，因为在第一种情况下
临时对象被创建。
速度和性能可能有差异，也可能没有差别。它取决于你使用的C ++实现，优化等等的
干杯
-
Mateusz Loskot
你的意思是......性能，语义，......的差异？？
从语义上看，存在差异，因为在第一种情况下
临时对象被创建。
速度和性能可能有差异，也可能没有差别。它取决于您使用的C ++实现，优化等等
一般来说（和Cline等人的常见问题解答书同意： Q23.08），则应该使用前缀增量。原理是
，后缀运算符需要复制操作数，
递增操作数，然后返回副本的值;前缀
运算符只需要递增操作数并返回其值。
你的意思是......性能，语义，......的差异？在语义上，有区别因为在第一种情况下临时
对象已创建。
速度和性能可能有差异，也可能没有差别。它取决于您使用的C ++实现，优化等。
一般来说（和Cline等人的常见问题解答书同意：Q23.08），
如果操作数
的先前值被丢弃，则应该使用前缀增量，如上例所示。理由是
后缀运算符需要复制操作数，增加
操作数，然后返回副本的值;前缀运算符只是
需要递增操作数并返回其值。
出于兴趣，标准要求后缀版本是否需要* b $ b * *来制作副本？显然，它不会为int产生任何
的差异（我希望优化编译器在这里生成
相同的代码），但是在增量时一个具有非平凡的
复制构造函数的对象，它可能会有所作为。
-
Lionel B
Is there any difference between
for(int i = 0; some condition; i++)
{....}
and
for(int i = 0; some condition; ++i) ?
{....}
It seems not, by some experimenting, but I thought it was worth
checking since j++ and ++j usually mean different things in the
language ++c .
Thanks a lot,
Paul Epstein
You mean difference in...performance, semantic,...?
Semantically, there is a difference because in the first case
temporary object is created.
There may or may not be difference in speed and performance. it depends
on C++ implementation you use, optimization, etc.
Cheers
--
Mateusz Loskot
http://mateusz.loskot.net
You mean difference in...performance, semantic,...?
Semantically, there is a difference because in the first case
temporary object is created.
There may or may not be difference in speed and performance. it depends
on C++ implementation you use, optimization, etc.
Generally speaking (and the FAQ book from Cline et al concurs:
Q23.08), one should use the prefix increment if the previous value of
the operand is discarded, as in the example above. The rationale is
that the postfix operator needs to make a copy of the operand,
increment the operand, then return the value of the copy; the prefix
operator merely needs to increment the operand and return its value.
You mean difference in...performance, semantic,...?
Semantically, there is a difference because in the first case temporary
object is created.
There may or may not be difference in speed and performance. it depends
on C++ implementation you use, optimization, etc.
Generally speaking (and the FAQ book from Cline et al concurs: Q23.08),
one should use the prefix increment if the previous value of the operand
is discarded, as in the example above. The rationale is that the
postfix operator needs to make a copy of the operand, increment the
operand, then return the value of the copy; the prefix operator merely
needs to increment the operand and return its value.
Out of interest, does the standard mandate that the postfix version is
*required* to make a copy? Obviously it''s not going to make any
difference for an int (and I''d expect an optimising compiler to generate
identical code here), but when incrementing an object with a non-trivial
copy constructor it potentially could make a difference.
--
Lionel B
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