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cpy functions

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  cpy functions "Bill Cunningham" <nospam@nspam.invalid> - 2014-04-28 16:25 -0400
    Re: cpy functions John Gordon <gordon@panix.com> - 2014-04-28 20:42 +0000
      Re: cpy functions "Bill Cunningham" <nospam@nspam.invalid> - 2014-04-28 16:54 -0400
        Re: cpy functions Ben Bacarisse <ben.usenet@bsb.me.uk> - 2014-04-28 22:22 +0100
          Re: cpy functions "Bill Cunningham" <nospam@nspam.invalid> - 2014-04-28 17:26 -0400
        Re: cpy functions Richard <rgrdev_@gmail.com> - 2014-04-29 00:19 +0200
    Re: cpy functions Andrew Smallshaw <andrews@sdf.lonestar.org> - 2014-04-28 20:44 +0000
      Re: cpy functions Keith Thompson <kst-u@mib.org> - 2014-04-28 14:44 -0700
    Re: cpy functions Geoff <geoff@invalid.invalid> - 2014-04-28 13:55 -0700
      Re: cpy functions "Bill Cunningham" <nospam@nspam.invalid> - 2014-04-28 17:07 -0400
        Re: cpy functions Geoff <geoff@invalid.invalid> - 2014-04-28 14:13 -0700
          Re: cpy functions "Bill Cunningham" <nospam@nspam.invalid> - 2014-04-28 17:22 -0400
            Re: cpy functions "Bill Cunningham" <nospam@nspam.invalid> - 2014-04-28 17:32 -0400
            Re: cpy functions "Bill Cunningham" <nospam@nspam.invalid> - 2014-04-28 18:17 -0400
              Re: cpy functions jacob navia <jacob@spamsink.net> - 2014-04-29 00:43 +0200
                Re: cpy functions "Bill Cunningham" <nospam@nspam.invalid> - 2014-04-28 19:31 -0400
                  Re: cpy functions Ian Collins <ian-news@hotmail.com> - 2014-04-29 11:33 +1200
              Re: cpy functions Richard <rgrdev_@gmail.com> - 2014-04-29 02:27 +0200
            Re: cpy functions Barry Schwarz <schwarzb@dqel.com> - 2014-04-28 15:53 -0700
              Re: cpy functions "Bill Cunningham" <nosapm@nspam.invalid> - 2014-04-29 17:27 -0400
          Re: cpy functions Kaz Kylheku <kaz@kylheku.com> - 2014-04-28 21:55 +0000
            Re: cpy functions jacob navia <jacob@spamsink.net> - 2014-04-29 00:40 +0200
          Re: cpy functions Richard <rgrdev_@gmail.com> - 2014-04-29 00:20 +0200
        Re: cpy functions Ike Naar <ike@iceland.freeshell.org> - 2014-04-28 21:48 +0000
        Re: cpy functions Richard <rgrdev_@gmail.com> - 2014-04-29 00:20 +0200
        Re: cpy functions Barry Schwarz <schwarzb@dqel.com> - 2014-04-28 15:49 -0700
          Re: cpy functions "Bill Cunningham" <nospam@nspam.invalid> - 2014-04-28 19:33 -0400
      Re: cpy functions Ben Bacarisse <ben.usenet@bsb.me.uk> - 2014-04-28 22:13 +0100
    Re: cpy functions Keith Thompson <kst-u@mib.org> - 2014-04-28 14:19 -0700
      Re: cpy functions "Bill Cunningham" <nospam@nspam.invalid> - 2014-04-28 17:34 -0400
      Re: cpy functions "Bill Cunningham" <nospam@nspam.invalid> - 2014-04-28 17:44 -0400
        Re: cpy functions Barry Schwarz <schwarzb@dqel.com> - 2014-04-28 15:55 -0700
          Re: cpy functions Kaz Kylheku <kaz@kylheku.com> - 2014-04-28 23:19 +0000
            Re: cpy functions "Bill Cunningham" <nospam@nspam.invalid> - 2014-04-28 19:24 -0400
              Re: cpy functions "Bill Cunningham" <nospam@nspam.invalid> - 2014-04-28 19:26 -0400
                Re: cpy functions "Bill Cunningham" <nospam@nspam.invalid> - 2014-04-28 20:07 -0400
            Re: cpy functions "Bill Cunningham" <nosapm@nspam.invalid> - 2014-04-29 17:30 -0400
    Re: cpy functions Barry Schwarz <schwarzb@dqel.com> - 2014-04-28 15:43 -0700
      Re: cpy functions "Bill Cunningham" <nospam@nspam.invalid> - 2014-04-28 19:17 -0400
        Re: cpy functions "Bill Cunningham" <nospam@nspam.invalid> - 2014-04-28 19:35 -0400
    Re: cpy functions Michael Angelo Ravera <maravera@prodigy.net> - 2014-04-29 03:07 -0700
      Re: cpy functions Richard <rgrdev_@gmail.com> - 2014-04-29 12:59 +0200
        Re: cpy functions Ben Bacarisse <ben.usenet@bsb.me.uk> - 2014-04-29 13:58 +0100

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#43723 — cpy functions

    Is there a specific reason for using strcpy and memcpy for different 
uses? They look to me like the same thing.

Bill

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#43724

In <ljmdfj$su4$1@dont-email.me> "Bill Cunningham" <nospam@nspam.invalid> writes:

>     Is there a specific reason for using strcpy and memcpy for different 
> uses? They look to me like the same thing.

strcpy() takes two arguments.  memcpy() takes three arguments.  How can they
look the same?

-- 
John Gordon         Imagine what it must be like for a real medical doctor to
gordon@panix.com    watch 'House', or a real serial killer to watch 'Dexter'.

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#43728

"John Gordon" <gordon@panix.com> wrote in message 
news:ljmeg4$o59$1@reader1.panix.com...
> In <ljmdfj$su4$1@dont-email.me> "Bill Cunningham" <nospam@nspam.invalid> 
> writes:
>
>>     Is there a specific reason for using strcpy and memcpy for different
>> uses? They look to me like the same thing.
>
> strcpy() takes two arguments.  memcpy() takes three arguments.  How can 
> they
> look the same?
>
    You are ulminately moving values. If I've been understanding right. You 
can use casts with memcpy and pretty much move strings. Everything a value 
in memory. I have never used these two functions. I was just wondering if 
anyone out there has and what's the practical uses of having two functions 
that do the samething it seems to me anyway.

Bill
<shrug>

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#43738

"Bill Cunningham" <nospam@nspam.invalid> writes:

> "John Gordon" <gordon@panix.com> wrote in message 
> news:ljmeg4$o59$1@reader1.panix.com...
>> In <ljmdfj$su4$1@dont-email.me> "Bill Cunningham" <nospam@nspam.invalid> 
>> writes:
>>
>>>     Is there a specific reason for using strcpy and memcpy for different
>>> uses? They look to me like the same thing.
>>
>> strcpy() takes two arguments.  memcpy() takes three arguments.  How can 
>> they
>> look the same?
>>
>     You are ulminately moving values. If I've been understanding right. You 
> can use casts with memcpy and pretty much move strings.

No, you are not understanding correctly.  No cast is needed to copy a
string using memcpy.

> Everything a value 
> in memory. I have never used these two functions. I was just wondering if 
> anyone out there has

I wonder if there is anyone out there who has not -- they must be
amongst the most used C functions.  Anyway, the reasons to use one rather
than the other derive from the differences between them that are spelt
out in the specification or the man pages.  (I'm not being cryptic, I
just think there is more chance you'll remember the differences if you
find out for yourself.)

> and what's the practical uses of having two functions 
> that do the samething it seems to me anyway.

Read the man pages and try to work out why for yourself.  In fact, I'd
advice you not to read any more answers in the thread until you do,
because the strategy you seem to have been using so far (which is to ask
for explicit answers) does not seem to work for you.

-- 
Ben.

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#43739

"Ben Bacarisse" <ben.usenet@bsb.me.uk> wrote in message

> No, you are not understanding correctly.  No cast is needed to copy a
> string using memcpy.

 Right yes. That's a generic pointer I mispoke. No casts needed.

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#43757

"Bill Cunningham" <nospam@nspam.invalid> writes:

> "John Gordon" <gordon@panix.com> wrote in message 
> news:ljmeg4$o59$1@reader1.panix.com...
>> In <ljmdfj$su4$1@dont-email.me> "Bill Cunningham" <nospam@nspam.invalid> 
>> writes:
>>
>>>     Is there a specific reason for using strcpy and memcpy for different
>>> uses? They look to me like the same thing.
>>
>> strcpy() takes two arguments.  memcpy() takes three arguments.  How can 
>> they
>> look the same?
>>
>     You are ulminately moving values. If I've been understanding right. You 
> can use casts with memcpy and pretty much move strings. Everything a value 
> in memory. I have never used these two functions. I was just wondering
> if 

Yes you have Bill.

6/10


> anyone out there has and what's the practical uses of having two functions 
> that do the samething it seems to me anyway.
>
> Bill
> <shrug>
>

-- 
"Avoid hyperbole at all costs, its the most destructive argument on
the planet" - Mark McIntyre in comp.lang.c

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#43726

On 2014-04-28, Bill Cunningham <nospam@nspam.invalid> wrote:
>     Is there a specific reason for using strcpy and memcpy for different 
> uses? They look to me like the same thing.

strcpy() copys C strings - i.e. it stops as soon as it encounters
a terminating NULL character.  memcpy() copies the specified number
of bytes regardless of the contents of those bytes.

-- 
Andrew Smallshaw
andrews@sdf.lonestar.org

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#43746

Andrew Smallshaw <andrews@sdf.lonestar.org> writes:
> On 2014-04-28, Bill Cunningham <nospam@nspam.invalid> wrote:
>>     Is there a specific reason for using strcpy and memcpy for different 
>> uses? They look to me like the same thing.
>
> strcpy() copys C strings - i.e. it stops as soon as it encounters
> a terminating NULL character.  memcpy() copies the specified number
> of bytes regardless of the contents of those bytes.

NULL is (a macro that expands to) a null *pointer* constant.  You're
thinking of the null character (sometimes called NUL), '\0'.

(Unfortunately, due to a quirk in the way null pointer constants are
defined, you can sometimes get away with using NULL to represent a null
character.)

-- 
Keith Thompson (The_Other_Keith) kst-u@mib.org  <http://www.ghoti.net/~kst>
Working, but not speaking, for JetHead Development, Inc.
"We must do something.  This is something.  Therefore, we must do this."
    -- Antony Jay and Jonathan Lynn, "Yes Minister"

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#43729

On Mon, 28 Apr 2014 16:25:27 -0400, "Bill Cunningham"
<nospam@nspam.invalid> wrote:

>    Is there a specific reason for using strcpy and memcpy for different 
>uses? They look to me like the same thing.
>
>Bill
>

They are quite different.

As the name implies, strcpy expects a valid C string in the source
argument. A C string is a string of non-zero characters terminated by
a zero character. If it's not a valid C string it will copy
everything, including data you don't expect, up to the first zero
char, into the destination. This can overflow your destination,
leading to unexpected and unintended behavior in your program.

memcpy is somewhat more safe. Memcpy doesn't manipulate C strings,
only bytes, it knows nothing of zero termination it copies without
judgement of the content it's copying. It takes three arguments, a
destination, a source and a length. As long as length is <= the size
of destination the copy will only copy the number of bytes that
destination is expected to hold. Of course, you can still create
problems for yourself if the source and destinations overlap or if you
use a length greater than the destination.

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#43730

"Geoff" <geoff@invalid.invalid> wrote in message 
news:p4ftl9p41bj9nktk2b71lqfgbeuq2jseg0@4ax.com...

[...]

> memcpy is somewhat more safe. Memcpy doesn't manipulate C strings,
> only bytes, it knows nothing of zero termination it copies without
> judgement of the content it's copying. It takes three arguments, a
> destination, a source and a length. As long as length is <= the size
> of destination the copy will only copy the number of bytes that
> destination is expected to hold. Of course, you can still create
> problems for yourself if the source and destinations overlap or if you
> use a length greater than the destination.

char *a="String one";
char *b="String two";

memcpy(a,b,sizeof(a+b));

Is that a "strcpy" like representation? Atleast to an extent.

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#43732

On Mon, 28 Apr 2014 17:07:31 -0400, "Bill Cunningham"
<nospam@nspam.invalid> wrote:

>
>"Geoff" <geoff@invalid.invalid> wrote in message 
>news:p4ftl9p41bj9nktk2b71lqfgbeuq2jseg0@4ax.com...
>
>[...]
>
>> memcpy is somewhat more safe. Memcpy doesn't manipulate C strings,
>> only bytes, it knows nothing of zero termination it copies without
>> judgement of the content it's copying. It takes three arguments, a
>> destination, a source and a length. As long as length is <= the size
>> of destination the copy will only copy the number of bytes that
>> destination is expected to hold. Of course, you can still create
>> problems for yourself if the source and destinations overlap or if you
>> use a length greater than the destination.
>
>char *a="String one";
>char *b="String two";
>
>memcpy(a,b,sizeof(a+b));
WTF!---------------^^^

That is wrong on two levels:
1. You don't SUM two lengths to get the destination length.
2. You don't SUM two pointers to get the length of anything.

>
>Is that a "strcpy" like representation? Atleast to an extent.
>
No, it's not even close.
If you are going to use strings explicitly then use strcpy.

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#43737

"Geoff" <geoff@invalid.invalid> wrote in message 
news:psgtl9ptuqkd1bs2bo0a2nli40ujistbhe@4ax.com...

[...]


>>char *a="String one";
>>char *b="String two";
>>
>>memcpy(a,b,sizeof(a+b));
> WTF!---------------^^^
>
> That is wrong on two levels:
> 1. You don't SUM two lengths to get the destination length.
> 2. You don't SUM two pointers to get the length of anything.
>
>>
>>Is that a "strcpy" like representation? Atleast to an extent.
>>
> No, it's not even close.
> If you are going to use strings explicitly then use strcpy.

Sorry about my bad code. I am saying a "C String" *is* a bytestream. void* 
can take the char * and You can manipulate that 3rd parameter and use use 
memcpy. For example.

strtol (a,NULL,10)

is essentially
atoi(a)

excepting aoti doesn't return error code. So we need strtol. And you can 
course convert to all but some of the str in strtol.

strtol (a,b,10);

Am I getting this out? C Strings are /unraw/ C bytes. They can /somehow/ 
represent strings and be used like strcpy.

K That's I'm done. I can't really and any more.

Bill

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#43741

"Bill Cunningham" <nospam@nspam.invalid> wrote in message 
news:ljmgqh$m5k$1@dont-email.me...
>
> "Geoff" <geoff@invalid.invalid> wrote in message 
> news:psgtl9ptuqkd1bs2bo0a2nli40ujistbhe@4ax.com...
>
> [...]
>
>
>>>char *a="String one";
>>>char *b="String two";
>>>
>>>memcpy(a,b,sizeof(a+b));
>> WTF!---------------^^^
>>
>> That is wrong on two levels:
>> 1. You don't SUM two lengths to get the destination length.
>> 2. You don't SUM two pointers to get the length of anything.
>>
>>>
>>>Is that a "strcpy" like representation? Atleast to an extent.
>>>
>> No, it's not even close.
>> If you are going to use strings explicitly then use strcpy.
>
> Sorry about my bad code. I am saying a "C String" *is* a bytestream. void* 
> can take the char * and You can manipulate that 3rd parameter and use use 
> memcpy. For example.
>
> strtol (a,NULL,10)
>
> is essentially
> atoi(a)
>
> excepting aoti doesn't return error code. So we need strtol. And you can 
> course convert to all but some of the str in strtol.
>
> strtol (a,b,10);
>
> Am I getting this out? C Strings are /unraw/ C bytes. They can /somehow/ 
> represent strings and be used like strcpy.
>
> K That's I'm done. I can't really and any more.

    For some reason today. I can't type. That's supposed to read /raw/ 
bytes. Wheww.
-------
>> That is wrong on two levels:
>> 1. You don't SUM two lengths to get the destination length.
>> 2. You don't SUM two pointers to get the length of anything.

But if *I did* it right. :( Well do you see what I mean?

l8r 

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#43755

"Bill Cunningham" <nospam@nspam.invalid> wrote in message 
news:ljmgqh$m5k$1@dont-email.me...
>
> "Geoff" <geoff@invalid.invalid> wrote in message

> Sorry about my bad code. I am saying a "C String" *is* a bytestream. void* 
> can take the char * and You can manipulate that 3rd parameter and use use 
> memcpy. For example.
[...]

I'm not a C programmer. Just a wannabe and that's because the *nix system 
interface is in C. Otherwise C++ would probably be much simpler. But when 
you got a goal you have to take steps. I can sense C is very powerful and 
versatile.

Bill

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#43765

Le 29/04/2014 00:17, Bill Cunningham a écrit :
> I'm not a C programmer. Just a wannabe and that's because the *nix system
> interface is in C. Otherwise C++ would probably be much simpler.

11/10 Bill!

Of course C++ is simpler than C. Go spam comp.lang.c++, it is right 
around the corner, and it has much more people to spam than this one.

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#43780

"jacob navia" <jacob@spamsink.net> wrote in message 
news:ljmlje$298$3@speranza.aioe.org...
> Of course C++ is simpler than C. Go spam comp.lang.c++, it is right around 
> the corner, and it has much more people to spam than this one.

    And what would you do without me? Come on. I'm such a regular poster... 
You would remember me if I didn't post for 2 years. You need me!

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#43782

Bill Cunningham wrote:
> "jacob navia" <jacob@spamsink.net> wrote in message
> news:ljmlje$298$3@speranza.aioe.org...
>> Of course C++ is simpler than C. Go spam comp.lang.c++, it is right around
>> the corner, and it has much more people to spam than this one.
>
>      And what would you do without me? Come on. I'm such a regular poster...
> You would remember me if I didn't post for 2 years. You need me!

Bill the traffic generator?

-- 
Ian Collins

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#43792

"Bill Cunningham" <nospam@nspam.invalid> writes:

> "Bill Cunningham" <nospam@nspam.invalid> wrote in message 
> news:ljmgqh$m5k$1@dont-email.me...
>>
>> "Geoff" <geoff@invalid.invalid> wrote in message
>
>> Sorry about my bad code. I am saying a "C String" *is* a bytestream. void* 
>> can take the char * and You can manipulate that 3rd parameter and use use 
>> memcpy. For example.
> [...]
>
> I'm not a C programmer. Just a wannabe and that's because the *nix system 
> interface is in C. Otherwise C++ would probably be much simpler. But
> when 

C++ would be much simpler! LOL! You crack me up!

12/10

> you got a goal you have to take steps. I can sense C is very powerful and 
> versatile.
>
> Bill
>

-- 
"Avoid hyperbole at all costs, its the most destructive argument on
the planet" - Mark McIntyre in comp.lang.c

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#43768

On Mon, 28 Apr 2014 17:22:29 -0400, "Bill Cunningham"
<nospam@nspam.invalid> wrote:

<snip quoted text from a different author>

>Sorry about my bad code. I am saying a "C String" *is* a bytestream. void* 
>can take the char * and You can manipulate that 3rd parameter and use use 
>memcpy. For example.
>
>strtol (a,NULL,10)
>
>is essentially
>atoi(a)
>
>excepting aoti doesn't return error code. So we need strtol. And you can 

Don't you think it matters that atoi returns an int while strtol
returns a long?

>course convert to all but some of the str in strtol.
>
>strtol (a,b,10);

Sorry, I cannot make any sense of this.

-- 
Remove del for email

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#43845

"Barry Schwarz" <schwarzb@dqel.com> wrote in message

>>strtol (a,b,10);
>
> Sorry, I cannot make any sense of this.

    This is certainly deserving of a response. I have never used strtol like 
this. I have always used NULL as that second parameter. But I know the 2d 
parameter takes an "end pointer" which must be a char **. My example is 
probably sad. As I say I've never used an end pointer. Remember to I am 
*not* a C programmer. Just an amateur and have other things to do than be on 
usenet constantly watching clc or anything else. There are alot of seasoned 
programmers around here.
    But my understanding of strtol. That b would be a char ** though. To my 
understanding as an amateur.

    So much for struct addrinfo ;) right now.

Bill

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