高效的字符串反转代码 [英] Highly efficient string reversal code

问题描述

你好，我是一位经验丰富的专家C程序员，我写了这个代码来反转一个字符串。
我想你们都可以从中学到一些东西！


int reverse（char * reverseme）{

int retval = - 1;

if（retval！= NULL）{

int len = strlen（retval）{

if（len> 0）{

int half = len>> 1;

for（; retval< half; retval ++）{

reverseme [retval] ^ = reverseme [ len-（retval + 1）];

reverseme [len-（retval + 1）] = reverseme [retval];

reverseme [retval] ^ = reverseme [len - （retval + 1）];

}

}

}

返回retval;

}


-Phil / CERisE

解决方案

做************** @ ymail.com 写道：
< blockquote class =post_quotes>
你好，我是一位经验丰富的专家C程序员

不，你不是。

我写了

此代码用于反转字符串。我想你们都可以从中学到一些东西！

我对此表示怀疑。你应该重新考虑一下。它不是，因为你主题

声称高效。

2008年9月22日14:42，在comp。 lang.c，做************** @ ymail。 com

（do**************@ymail.com）写道：

你好，我是一位经验丰富的专家C程序员

显然，你是自负的，并且

b）错误

我写了

此代码用于反转字符串。

我/是/对不起，包括你和你的雇主。

我想你可以所有学习

来自它！

我确定你是对的。毕竟，/ I /得知你比你声称的C程序员要少得多。

int reverse（char * reverseme）{

int retval = -1;

if（retval！= NULL）

无用测试，因为retval被初始化（并且从未改变）到一个不等于NULL的值

{

int len = strlen（retval）

第一次真正的失败。 retval是一个整数，并且

strlen（）的参数是一个指向char的指针。使用字符串长度时，您无法从

获得有效结果。一个整数。


第二次失败：你没有#include声明

strlen（）函数的标题。因此，您的编译器没有将上述

赋值标记为错误（不兼容类型的参数）

{

if（len> 0）

那么，字符串长度是多少？整数？什么时候它会大于零？
$ blockquote class =post_quotes>
{

int half = len>> 1 ;

样式黑客：为了更清楚地知道半数代表什么类型的数字

，你应该将其编码为

int half = len / 2;

当然，由于len是无意义的值，因此一半也将是

无意义的值。

for（; retval< half; retval ++）{

reverseme [retval] ^ = reverseme [len-（retval + 1）] ;

第一次迭代时未定义的行为，当retval == -1

reverseme [-1]超出范围时。

reverseme [len-（retval + 1）] = reverseme [retval];

第一次迭代时未定义的行为 - 同样的原因

reverseme [retval] ^ = reverseme [len-（RETVAL + 1）];

第一次迭代时未定义的行为 - 同样的原因


另外，你搞砸了xor技巧 ，和/ / / $ / $
字符串末尾的值无效。


头端现在包含一个0x00的数组（最多

错误计算的中点），而尾端包含头端xor尾部的

结果。

}

}

}

返回retval;

此返回值的用途是什么？

}


-Phil / CERisE

-

Lew Pitcher


Master Codewright& amp ; JOAT-in-training |已注册的Linux用户＃112576
http://pitcher.digitalfreehold.ca/ |可根据要求提供GPG公钥

---------- Slackware - 因为我知道我在做什么。 ------

做**************@ymail.com 写道：

你好，我是一位经验丰富的专家C程序员[...]

s / C程序员/ PLONKed巨魔/

-
Er ********* @ sun.com

Hello, I''m a highly experienced expert C programmer and I''ve written
this code to reverse a string in place. I think you could all learn
something from it!

int reverse(char* reverseme){
int retval=-1;
if(retval!=NULL){
int len=strlen(retval){
if(len>0){
int half=len>>1;
for(;retval<half;retval++){
reverseme[retval]^=reverseme[len-(retval+1)];
reverseme[len-(retval+1)]=reverseme[retval];
reverseme[retval]^=reverseme[len-(retval+1)];
}
}
}
return retval;
}

-Phil/CERisE

解决方案

do**************@ymail.com wrote:

Hello, I''m a highly experienced expert C programmer

No, you are not.

and I''ve written
this code to reverse a string in place. I think you could all learn
something from it!

I doubt it. You should rethink it. It is not, as you subject line
claims "highly efficient".

On September 22, 2008 14:42, in comp.lang.c, do**************@ymail.com
(do**************@ymail.com) wrote:

Hello, I''m a highly experienced expert C programmer

Apparently, you are
a) egotistical, and
b) wrong

and I''ve written
this code to reverse a string in place.

I am /so/ sorry, both for you and your employer.

I think you could all learn
something from it!

I''m sure that you are right. After all, /I/ learned that you are much less
than the C programmer that you claim to be.

int reverse(char* reverseme){
int retval=-1;
if(retval!=NULL)

Useless test, as retval was initialized (and never altered) to a value
that will not equate to NULL

{
int len=strlen(retval)

First real failure. retval is an integer, and the argument to
strlen() is a pointer-to-char. You can''t get a valid result from
taking the "string length" of an integer.

Second failure: you did not #include the header that declares the
strlen() function. Thus, your compiler did not flag the above
assignment as an error (argument of incompatable type)

{
if(len>0)

So, what is the "string length" of an integer? And when would it be
greater than zero?

{
int half=len>>1;

Style hack: To be clearer to the intent of what sort of number
half represents, you should have coded this as
int half = len / 2;
Of course, since len is a nonsense value, half will also be a
nonsense value.

for(;retval<half;retval++){
reverseme[retval]^=reverseme[len-(retval+1)];

Undefined behaviour on first iteration, when retval == -1
reverseme[-1] is out of bounds.

reverseme[len-(retval+1)]=reverseme[retval];

Undefined behaviour on first iteration - same reason

reverseme[retval]^=reverseme[len-(retval+1)];

Undefined behaviour on first iteration - same reason

Plus, you''ve screwed up the "xor trick", and wiped out /both/
ends of the string with invalid values.

The head end now contains an array of 0x00 (up to
the ill-computed "midpoint"), while the tail end contains the
results of the head end xor the tail end.

}
}
}
return retval;

Of what use is this return value?

}

-Phil/CERisE

--
Lew Pitcher

Master Codewright & JOAT-in-training | Registered Linux User #112576
http://pitcher.digitalfreehold.ca/ | GPG public key available by request
---------- Slackware - Because I know what I''m doing. ------

do**************@ymail.com wrote:

Hello, I''m a highly experienced expert C programmer [...]

s/C programmer/PLONKed troll/

--
Er*********@sun.com

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