Is it possible sentence?

[Alex]

Hi,

I have a question regarding to string variable.

Please look at below example.
------------------------------
#define STR "ABC"

char *testStr
testStr = STR;
------------------------------

I think above example have no problem.
But I don't know where "ABC" is exist.
Does C compiler make a memory for STR?

-Alex-

[Vijay Kumar R Zanvar]

"Alex" <dr******@korea .com> wrote in message news:7a******** *************** ***@posting.goo gle.com...

Hi,

I have a question regarding to string variable.

Please look at below example.
------------------------------
#define STR "ABC"

char *testStr
testStr = STR;
This is perfectly correct if it appears inside a function. A statement
in C must always be within a compound block.
------------------------------

I think above example have no problem.
But I don't know where "ABC" is exist.
Does C compiler make a memory for STR?

Your question, in general, is about storage of string literals. The answer
varies under the following situations:

* The Standard recommends the string literal to be a read-only; thus,
allows sharing copies of string with identical text. In this
case, the implementation may store the sting in the code section,
or any other read-only section. This method helps perform some
optimizations.

* Many implementation provide extensions which are, generally, non
portable. One such extension is writable string literals. The
string is, then, stored in the program's static region. Thus, there
would be different copies of string literal of identical text.

Many compilers provide option to control the behaviour of character string
literals. For example, gcc provide a compiler switch, -fwritable-strings, to
store strings in writable data section. By default, GCC merges duplicate
strings, whereas, Borland's Turbo C/C++ doesn't. It provides the following
switches:

-d merge duplicate string on
-d- merge duplicate string off

Many compilers provide pragmas to control, but these are non portable.
The Standard(C99) specifies only few pragmas that are portable, and is out of
scope here.
-Alex-

--
Vijay Kumar R Zanvar
My Home Page - http://www.geocities.com/vijoeyz/

[Vijay Kumar R Zanvar]

"Vijay Kumar R Zanvar" <vi*****@global edgesoft.com> wrote in message news:2j******** *****@uni-berlin.de...

"Alex" <dr******@korea .com> wrote in message news:7a******** *************** ***@posting.goo gle.com...

Hi,

I have a question regarding to string variable.

Please look at below example.
------------------------------
#define STR "ABC"

char *testStr
Ah..missing semicolon.
testStr = STR;

[Chris Dollin]

Alex wrote:

I have a question regarding to string variable.

Please look at below example.
------------------------------
#define STR "ABC"

char *testStr
(missing ;)
testStr = STR;
(illegal at top level; assume we rewrite to

chat *testStr = STR;
)
------------------------------

I think above example have no problem.
But I don't know where "ABC" is exist.
Somewhere. Somewhere where it will be valid for the
entire program run. You don't need to know where.
Does C compiler make a memory for STR?

Yes, but irrelevant; STR is a preprocessor symbol and is not visible
at run-time (and need not and usually is not in compiled object code).

--
Chris "electric hedgehog" Dollin
C FAQs at: http://www.faqs.org/faqs/by-newsgrou...mp.lang.c.html
C welcome: http://www.angelfire.com/ms3/bchambl...me_to_clc.html

[Irrwahn Grausewitz]

dr******@korea. com (Alex) wrote:

Hi,

I have a question regarding to string variable.

Please look at below example.
------------------------------
#define STR "ABC"

char *testStr
testStr = STR;
------------------------------

I think above example have no problem.
But I don't know where "ABC" is exist.
Does C compiler make a memory for STR?

No. First, every occurrence of STR is literally replaced with "ABC"
by the C preprocessor. Later in translation "ABC", like every source
code string literal, is translated into an anonymous array object
(in C the term 'object' means 'region of data storage which can hold
values').

Regards
--
Irrwahn Grausewitz (ir*******@free net.de)
welcome to clc: http://www.ungerhu.com/jxh/clc.welcome.txt
clc faq-list : http://www.faqs.org/faqs/C-faq/faq/
clc OT guide : http://benpfaff.org/writings/clc/off-topic.html

[Dan Pop]

In <7a************ **************@ posting.google. com> dr******@korea. com (Alex) writes:

I have a question regarding to string variable.

Please look at below example.
------------------------------
#define STR "ABC"

char *testStr;
testStr = STR;
------------------------------

I think above example have no problem.
Indeed, it is correct (after fixing an obvious typo).
But I don't know where "ABC" is exist.
It is typically stored in either the data segment or the text segment
of the program. If you can change it at runtime without crashing the
program, then it's probably in the data segment. If the program crashes,
it's in the text segment. Let's see:

fangorn:~/tmp 192> cat test.c
#define STR "ABC"

int main()
{
char *testStr;
testStr = STR;
*testStr = 0;
return *testStr;
}
fangorn:~/tmp 193> gcc test.c
fangorn:~/tmp 194> ./a.out
Segmentation fault

So, it was in the text segment on my system/compiler combo.
Some compilers allow the user to control this aspect:

fangorn:~/tmp 195> gcc -fwritable-strings test.c
fangorn:~/tmp 196> ./a.out
fangorn:~/tmp 197> echo $status
0
Does C compiler make a memory for STR?

The STR identifier exists only during the preprocessing phase. By the
time the proper compilation starts, it has already been replaced by the
"ABC" string literal, so the compiler doesn't even get to "see" it.

Dan
--
Dan Pop
DESY Zeuthen, RZ group
Email: Da*****@ifh.de

[Ralmin]

"Dan Pop" <Da*****@cern.c h> wrote:

dr******@korea. com (Alex) writes:

#define STR "ABC"

char *testStr;

Note: the semicolon in the above line was added by Dan, and was not in
Alex's original post.

Dan, lest anyone accuse you of turning into another ERT, please strictly
uphold the rules of quoting. The most one should do to quoted text is to
snip out parts or to reflow the text for a consistent line length. It is not
acceptable to silently make additions, changes or improvements to someone's
code. At the least, the quote symbol on that line (>) should be removed to
indicate changes were made.

--
Simon.

[Jack Klein]

On Tue, 22 Jun 2004 17:30:17 +0530, "Vijay Kumar R Zanvar"
<vi*****@global edgesoft.com> wrote in comp.lang.c:

"Alex" <dr******@korea .com> wrote in message news:7a******** *************** ***@posting.goo gle.com...

Hi,

I have a question regarding to string variable.

Please look at below example.
------------------------------
#define STR "ABC"

char *testStr
testStr = STR;

This is perfectly correct if it appears inside a function. A statement
in C must always be within a compound block.

------------------------------

I think above example have no problem.
But I don't know where "ABC" is exist.
Does C compiler make a memory for STR?

Your question, in general, is about storage of string literals. The answer
varies under the following situations:

* The Standard recommends the string literal to be a read-only; thus,

The Standard makes no recommendations at all as to whether string
literals should be read-only or not. C++ defines string literals as
having type array of const char, but C does not. A C string literal
has the type of array of char, no const.

Modifying a string literal in C is undefined behavior because the
standard specifically states that it is, not because the characters
may or may not be read-only.

--
Jack Klein
Home: http://JK-Technology.Com
FAQs for
comp.lang.c http://www.eskimo.com/~scs/C-faq/top.html
comp.lang.c++ http://www.parashift.com/c++-faq-lite/
alt.comp.lang.l earn.c-c++
http://www.contrib.andrew.cmu.edu/~a...FAQ-acllc.html

[Jack Klein]

On 22 Jun 2004 13:25:48 GMT, Da*****@cern.ch (Dan Pop) wrote in
comp.lang.c:

In <7a************ **************@ posting.google. com> dr******@korea. com (Alex) writes:

I have a question regarding to string variable.

Please look at below example.
------------------------------
#define STR "ABC"

char *testStr;
testStr = STR;
------------------------------

I think above example have no problem.
Indeed, it is correct (after fixing an obvious typo).

But I don't know where "ABC" is exist.

It is typically stored in either the data segment or the text segment

Who says C programs have data segments and text segments? Chapter and
verse.
of the program. If you can change it at runtime without crashing the
program, then it's probably in the data segment. If the program crashes,
it's in the text segment. Let's see:

Let's not. A strictly conforming program can't tell what happens when
a string literal is changed, since it ceases to be strictly conforming
when it tries to perform the change.

In most of the environments where the code I get paid to write
executes, the undefined behavior of attempting to modify a string
literal is ... nothing at all. The EPROM or Flash device in which the
string literal is stored is totally unaffected by anything the
processor can do to it in normal execution.

--
Jack Klein
Home: http://JK-Technology.Com
FAQs for
comp.lang.c http://www.eskimo.com/~scs/C-faq/top.html
comp.lang.c++ http://www.parashift.com/c++-faq-lite/
alt.comp.lang.l earn.c-c++
http://www.contrib.andrew.cmu.edu/~a...FAQ-acllc.html

[Dan Pop]

In <db************ *************** ***@news.terane ws.com> "Ralmin" <ne**@ralminNOS PAM.cc> writes:

"Dan Pop" <Da*****@cern.c h> wrote:

dr******@korea. com (Alex) writes:

> #define STR "ABC"
>
> char *testStr;

Note: the semicolon in the above line was added by Dan, and was not in
Alex's original post.

Why would anyone bother to note such an irrelevant detail? Does it make
any difference to the OP question or to my reply?
Dan, lest anyone accuse you of turning into another ERT, please strictly
uphold the rules of quoting. The most one should do to quoted text is to
snip out parts or to reflow the text for a consistent line length. It is not
acceptable to silently make additions, changes or improvements to someone's
code. At the least, the quote symbol on that line (>) should be removed to
indicate changes were made.
Did you read the rest of my post with your brain engaged? Here's the
relevant part:
I have a question regarding to string variable.

Please look at below example.
------------------------------
#define STR "ABC"

char *testStr;
testStr = STR;
------------------------------

I think above example have no problem.

Indeed, it is correct (after fixing an obvious typo).
^^^^^^^^^^^^^^^ ^^^^^^^^^^^^^^^
In your humble opinion, what was the purpose of the parenthetical
remark underlined above?

The intent of the OP was perfectly clear, despite the missing semicolon
in the original code. If I had any good reason to suspect that the OP
omitted it *by ignorance*, I would have pointed out the syntax error.
In the absence of any such reason, it was more constructive to fix the
code AND mention that I've fixed it, rather than waste time uselessly
pointing out the missing semicolon. I keep forgetting semicolons myself,
on a regular basis, because my brain is focused on more important things
when typing C code.

It is not the first time I'm correcting trivial typos in posted code
and expect a much harsher reply the next time you choose to make a
fuss out of it.

Dan
--
Dan Pop
DESY Zeuthen, RZ group
Email: Da*****@ifh.de