strcat() - 未名空间MITBBS历史存档

国际科技财经博客移民网络热点娱乐民生时事公众号

Redian新闻

>未名空间

>Programming - 葵花宝典

strcat()

strcat()# Programming - 葵花宝典

C*Q2008-03-09 08:03

1 楼

【以下文字转载自 Immigration 讨论区】
发信人: CandyQQ (甜甜糖), 信区: Immigration
标题: 配偶加入485申请的问题
发信站: BBS 未名空间站 (Wed Oct 29 21:40:13 2008)
比如说主申请人的绿卡申请priority date是2006年10月份，在2007年7月份那拨已经提
交了485. 如果现在马上结婚的话，配偶可不可以也提交485? (考虑到现在排期只有排
到2004年)

i*p2008-03-09 08:03

2 楼

char s1[] = "Hello ";
char s2[] = "world";
char *s3;
s3 = strcat(s1, s2);
It is Ok. Both s1 and s3 will be "Hello world".
char *s1 = "Hello ";
char s2[] = "world";
char *s3;
s3 = strcat(s1, s2);
It is runtime error. Can you explain?

s*x2008-03-09 08:03

3 楼

同问~ thx

P*e2008-03-09 08:03

4 楼

strcat(char*, const char*)
s1必须是char *;
char *s1 = "hello";
s1是指向 const char*的，因为s1是desti

【在 i**p 的大作中提到】

: char s1[] = "Hello ";
: char s2[] = "world";
: char *s3;
: s3 = strcat(s1, s2);
: It is Ok. Both s1 and s3 will be "Hello world".
: char *s1 = "Hello ";
: char s2[] = "world";
: char *s3;
: s3 = strcat(s1, s2);
: It is runtime error. Can you explain?

i*p2008-03-09 08:03

5 楼

Do you mean
char *s1 = "hello"; s1 points to a const string?

【在 P********e 的大作中提到】

: strcat(char*, const char*)
: s1必须是char *;
: char *s1 = "hello";
: s1是指向 const char*的，因为s1是desti

P*e2008-03-09 08:03

6 楼

恩

【在 i**p 的大作中提到】

: Do you mean
: char *s1 = "hello"; s1 points to a const string?

d*22008-03-09 08:03

7 楼

you totally mess up the memory. s1 must be allocated with enough space first
.

i*p2008-03-09 08:03

8 楼

How about
char s1[] = "hello";
I think the size of s1 has been set to 6. how does it work?

【在 P********e 的大作中提到】

: 恩

i*p2008-03-09 08:03

9 楼

How does it work?
char s1[] = "Hello ";
char s2[] = "world";
char *s3;
s3 = strcat(s1, s2);
Both s1 and s3 will be "Hello world".

【在 i**p 的大作中提到】

: How about
: char s1[] = "hello";
: I think the size of s1 has been set to 6. how does it work?

d*22008-03-09 08:03

10 楼

it does not work. any c programmer writes this way should be hanged.

【在 i**p 的大作中提到】

: How does it work?
: char s1[] = "Hello ";
: char s2[] = "world";
: char *s3;
: s3 = strcat(s1, s2);
: Both s1 and s3 will be "Hello world".

i*p2008-03-09 08:03

11 楼

I run it by VC. It prints both s1 and s3 as "hello world".

【在 d****2 的大作中提到】

:
: it does not work. any c programmer writes this way should be hanged.

t*t2008-03-09 08:03

12 楼

运行结果正确不代表你的程序就是正确的

【在 i**p 的大作中提到】

: I run it by VC. It prints both s1 and s3 as "hello world".

i*p2008-03-09 08:03

13 楼

then what tool can help us to find this programming error?

【在 t****t 的大作中提到】

: 运行结果正确不代表你的程序就是正确的

d*22008-03-09 08:03

14 楼

that is a good research question. MSFT will be very interested to fix their
crappy code base.

【在 i**p 的大作中提到】

: then what tool can help us to find this programming error?

i*p2008-03-09 08:03

15 楼

A good compiler should at least give a waring, but VC++ does not.

their

【在 d****2 的大作中提到】

:
: that is a good research question. MSFT will be very interested to fix their
: crappy code base.

d*22008-03-09 08:03

16 楼

google buffer overflow.

【在 i**p 的大作中提到】

: A good compiler should at least give a waring, but VC++ does not.
:
: their

c*t2008-03-09 08:03

17 楼

Just forget using strcat function. sprintf and strcpy are
less error prone.

【在 i**p 的大作中提到】

: A good compiler should at least give a waring, but VC++ does not.
:
: their

t*t2008-03-09 08:03

18 楼

name a compiler that will give a warning for this.

【在 i**p 的大作中提到】

: A good compiler should at least give a waring, but VC++ does not.
:
: their

m*e2008-03-09 08:03

19 楼

It's not ok. You just got lucky.

【在 i**p 的大作中提到】

: A good compiler should at least give a waring, but VC++ does not.
:
: their

O*d2008-03-09 08:03

20 楼

如果你把s1和s2中间插一个，看看能不能运行。再看一看_s1变成了什么。
char s1[] = "Hello ";
char _s1[] = "whatever";
char s2[] = "world";
char *s3;
s3 = strcat(s1, s2);
printf("s1 %s _s1 %s\n", s1, _s1);

【在 i**p 的大作中提到】

: I run it by VC. It prints both s1 and s3 as "hello world".

i*p2008-03-09 08:03

21 楼

I know what all of you talk about. see my original post. My qustion is s1[]
and *s1 have different result, which means *s1 is more protective than s1[].
Why not make them the same?
char s1[] = "Hello ";
char *s1 = "Hello ";

【在 O*******d 的大作中提到】

: 如果你把s1和s2中间插一个，看看能不能运行。再看一看_s1变成了什么。
: char s1[] = "Hello ";
: char _s1[] = "whatever";
: char s2[] = "world";
: char *s3;
: s3 = strcat(s1, s2);
: printf("s1 %s _s1 %s\n", s1, _s1);

d*22008-03-09 08:03

22 楼

char [] has space allocated on stack
char * is a pointer to static text area, write protected.
BTW, char [] and char * are different thing. Compiler does some translation
for you so you won't notice the difference most of time. Try sizeof(s1) in
both cases and you will know why.

i*p2008-03-09 08:03

23 楼

Of course, s1[] and *s1 are different. I have seen lots of programmer tried
to do something like “strcpy (s2, s1, sizeof(s1))” with s1 defined as *s1.
When is happened, I partly blame the programmer and mostly blame why C does
not do something to prevent this from the beginning or a latter improvement
. Anyway, this is a dangerous pitfall for a beginner and mostly to be an
interview question.
For the strcat(), it is much easier to generate a compiler warning or
runtime error for s1[] than *s1, b

【在 d****2 的大作中提到】

: char [] has space allocated on stack
: char * is a pointer to static text area, write protected.
: BTW, char [] and char * are different thing. Compiler does some translation
: for you so you won't notice the difference most of time. Try sizeof(s1) in
: both cases and you will know why.

t*t2008-03-09 08:03

24 楼

在你指责一个语言有这样那样的问题的时候, 有必要考虑语言设计时的历史环境. 为了
保持高速度, C语言里本来就没有数组边界检查, 更何况数组在函数调用里自动退化为指
针,数组尺寸信息早就没有了.
嫌C语言不安全的话,有很多更安全的语言可以用.就算是C++, 也有string class.
不过, 会在strcpy()里写上三个参数的, 可以想见你连门都没入. (FYI, 有三个参数的
那个叫做strncpy().) 门都没入的人还是虚心一点的好, 不要连纸上谈兵都谈不来,被人
笑掉大牙.

tried
s1.
does
improvement
an

【在 i**p 的大作中提到】

: Of course, s1[] and *s1 are different. I have seen lots of programmer tried
: to do something like “strcpy (s2, s1, sizeof(s1))” with s1 defined as *s1.
: When is happened, I partly blame the programmer and mostly blame why C does
: not do something to prevent this from the beginning or a latter improvement
: . Anyway, this is a dangerous pitfall for a beginner and mostly to be an
: interview question.
: For the strcat(), it is much easier to generate a compiler warning or
: runtime error for s1[] than *s1, b

d*22008-03-09 08:03

25 楼

funny, OP is asking beginner questions yet acts like a pro wannabe. no wonder such forums are boring. compiler is harder than you think.

i*p2008-03-09 08:03

26 楼

小屁孩拣了个大包子，乐得找不到了北。老哥虽民工出身，码砖的事早就不干了。听说
过大博士不知道１０００００００是负几吗？没听说过只能说你太嫩。我到是在民工
学徒其间老听到同道笑话师傅打字没他快，你也就和他有一比了。

为指
被人

【在 t****t 的大作中提到】

: 在你指责一个语言有这样那样的问题的时候, 有必要考虑语言设计时的历史环境. 为了
: 保持高速度, C语言里本来就没有数组边界检查, 更何况数组在函数调用里自动退化为指
: 针,数组尺寸信息早就没有了.
: 嫌C语言不安全的话,有很多更安全的语言可以用.就算是C++, 也有string class.
: 不过, 会在strcpy()里写上三个参数的, 可以想见你连门都没入. (FYI, 有三个参数的
: 那个叫做strncpy().) 门都没入的人还是虚心一点的好, 不要连纸上谈兵都谈不来,被人
: 笑掉大牙.
:
: tried
: s1.

m*e2008-03-09 08:03

27 楼

Please take your troll somewhere else.

【在 i**p 的大作中提到】

: 小屁孩拣了个大包子，乐得找不到了北。老哥虽民工出身，码砖的事早就不干了。听说
: 过大博士不知道１０００００００是负几吗？没听说过只能说你太嫩。我到是在民工
: 学徒其间老听到同道笑话师傅打字没他快，你也就和他有一比了。
:
: 为指
: 被人

t*t2008-03-09 08:03

28 楼

虽然不知道你说的是啥,不过常来的都知道,我不是靠写程序吃饭的

【在 i**p 的大作中提到】

n*t2008-03-09 08:03

29 楼

你真是小母牛选美啊。

【在 i**p 的大作中提到】

i*p2008-03-09 08:03

30 楼

Please understand it is not shame to 靠写程序吃饭. My point is you pay more
attention to my example strcpy. Thank you anyway since you posted a lot for
this topic even though I do not agree most of your answer.

【在 t****t 的大作中提到】

: 虽然不知道你说的是啥,不过常来的都知道,我不是靠写程序吃饭的

f*y2008-03-09 08:03

31 楼

You guys don't mention s2 at all? It probably will be "orld".

【在 i**p 的大作中提到】

: Please understand it is not shame to 靠写程序吃饭. My point is you pay more
: attention to my example strcpy. Thank you anyway since you posted a lot for
: this topic even though I do not agree most of your answer.