l******e
发帖数: 94 | 1 I found this question in CareerCup. someone there says ++a is faster, but i
don't know why?
Anybody can tell me the reason? | t*s
发帖数: 1504 | 2 a++ is faster
because a is closer to your finger, + is further away
when you type a++, you first type a, at the same time, your other hand has
already moved half way to +, so it saved significant time.
on the other hand, when you type ++a, your left hand is simply hanged there,
there is sync overhead.
i
【在 l******e 的大作中提到】
: I found this question in CareerCup. someone there says ++a is faster, but i
: don't know why?
: Anybody can tell me the reason?
| b***n
发帖数: 3 | 3 ft
there,
【在 t*s 的大作中提到】
: a++ is faster
: because a is closer to your finger, + is further away
: when you type a++, you first type a, at the same time, your other hand has
: already moved half way to +, so it saved significant time.
: on the other hand, when you type ++a, your left hand is simply hanged there,
: there is sync overhead.
:
: i
| l******e
发帖数: 94 | 4 tong ft. anyone here can tell me the real reason.
【在 b***n 的大作中提到】
: ft
:
: there,
| i****c
发帖数: 102 | 5 funny,haha
there,
【在 t*s 的大作中提到】
: a++ is faster
: because a is closer to your finger, + is further away
: when you type a++, you first type a, at the same time, your other hand has
: already moved half way to +, so it saved significant time.
: on the other hand, when you type ++a, your left hand is simply hanged there,
: there is sync overhead.
:
: i
| a****1
发帖数: 61 | 6 good reason. i usually type a++ rather than ++a.
there,
【在 t*s 的大作中提到】
: a++ is faster
: because a is closer to your finger, + is further away
: when you type a++, you first type a, at the same time, your other hand has
: already moved half way to +, so it saved significant time.
: on the other hand, when you type ++a, your left hand is simply hanged there,
: there is sync overhead.
:
: i
| c*****g
发帖数: 119 | 7 old question
http://www.parashift.com/c++-faq-lite/operator-overloading.html#faq-13.15
i
【在 l******e 的大作中提到】
: I found this question in CareerCup. someone there says ++a is faster, but i
: don't know why?
: Anybody can tell me the reason?
| m****0
发帖数: 30 | 8 ++a does not require allocating a temp variable while a++ does. | f**********n
发帖数: 3 | 9 no big deal, the compiler will optimize it
【在 m****0 的大作中提到】
: ++a does not require allocating a temp variable while a++ does.
| m****0
发帖数: 30 | 10 How does compiler optimize it in C++? | | | r***u
发帖数: 320 | 11 a++ is faster?
a++ read firstly, and then write.
++a is first write.
so cpu have to wait several cycles. (data hazard in Computer Architecture)
i
【在 l******e 的大作中提到】
: I found this question in CareerCup. someone there says ++a is faster, but i
: don't know why?
: Anybody can tell me the reason?
| m****0
发帖数: 30 | 12 Totally wrong!
This is c and c++ -- high level programming language.
In fact, for some programming language, there is no difference between pre-
increment and post-increment. However, in c++, when you learn operator
overloading, you will see the difference.
A typical implementation of post-increment is like this:
SomeType SomeType::operator++(int)
{
SomeType temp(*this); // save current object
operator++(); // increment internal state using pre-increment
return temp; /
【在 r***u 的大作中提到】
: a++ is faster?
: a++ read firstly, and then write.
: ++a is first write.
: so cpu have to wait several cycles. (data hazard in Computer Architecture)
:
: i
| k****z
发帖数: 550 | 13 This is overloading, a different question.
For the ++ operator for primitive types, compiler should have optimized it.
Anybody know the answer for primitive types?
【在 m****0 的大作中提到】
: Totally wrong!
: This is c and c++ -- high level programming language.
: In fact, for some programming language, there is no difference between pre-
: increment and post-increment. However, in c++, when you learn operator
: overloading, you will see the difference.
: A typical implementation of post-increment is like this:
: SomeType SomeType::operator++(int)
: {
: SomeType temp(*this); // save current object
: operator++(); // increment internal state using pre-increment
| r***u
发帖数: 320 | 14 you know there is efficiency issue in high language? compiler optimization
can't do everything.
【在 m****0 的大作中提到】
: Totally wrong!
: This is c and c++ -- high level programming language.
: In fact, for some programming language, there is no difference between pre-
: increment and post-increment. However, in c++, when you learn operator
: overloading, you will see the difference.
: A typical implementation of post-increment is like this:
: SomeType SomeType::operator++(int)
: {
: SomeType temp(*this); // save current object
: operator++(); // increment internal state using pre-increment
| m****0
发帖数: 30 | 15 You replied wrong person.
【在 r***u 的大作中提到】
: you know there is efficiency issue in high language? compiler optimization
: can't do everything.
| f*********y
发帖数: 43 | 16 for C, no difference, as I understand.
for class(STL etc) in C++, ++a is more efficient.
i
【在 l******e 的大作中提到】
: I found this question in CareerCup. someone there says ++a is faster, but i
: don't know why?
: Anybody can tell me the reason?
| c******e
发帖数: 82 | 17 Correct answer.
【在 f*********y 的大作中提到】
: for C, no difference, as I understand.
: for class(STL etc) in C++, ++a is more efficient.
:
: i
| x****u
发帖数: 44466 | 18 如果用的是任何C++标准iterator加上任何商用编译器，答案必然是一样。如果排除任
何一个前提，答案是不确定，hoho。
一定要看Inside C++ Object Model，Effective C++说的话没错，但是有强烈的误导性
。 |
|
