A question on string literals

[junky_fellow]

char *str1 = "Hello";
char arr1[] = { "Hello" };
char arr2[] = { 'H', 'e', 'l', 'l', 'o' };

Is it legal to modify str1, arr1 and arr2 ?

[Sriram Rajagopalan]

1.char *str1 = "Hello";

Generally the string literals would be stored in the read only data
section of the resulting object code, post compilation. So, modifying
the contents of the memory location addressed by "str1" would result in
seg fault. This might be compiler dependent though.

Although, "str1" itself can be modified.

The following is valid:
char *str1 = "Hello";
str1 = 0; // Allowed

2.char arr1[] = { "Hello" };

Contents of the memory addressed by "arr1" can be modified. "arr1"
itself cannot be modified.

That is the following is invalid:
char arr1[] = { "Hello" };
arr1 = 0; // Not allowed.

3. char arr2[] = { 'H', 'e', 'l', 'l', 'o' };

Same comments as above for "arr2" hold true here.

-Sriram.

[Krishanu Debnath]

junky_fel...@ya hoo.co.in wrote:

char *str1 = "Hello";
char arr1[] = { "Hello" };
char arr2[] = { 'H', 'e', 'l', 'l', 'o' };

Is it legal to modify str1, arr1 and arr2 ?

This is a FAQ. Read Question 1.32

http://www.eskimo.com/~scs/C-faq/faq.html

Krishanu

[Suman]

ju**********@ya hoo.co.in wrote:

char *str1 = "Hello";
char arr1[] = { "Hello" };
char arr2[] = { 'H', 'e', 'l', 'l', 'o' };

Is it legal to modify str1, arr1 and arr2 ?

FAQ 6.2 should be a good place to start.

To quote the draft:

The declaration
char arr1[] = { "Hello" };
defines a 'plain' char array object (of unknown size) `arr1' whose
elements
are initialized with character string literal. Array contents
are modifiable. This declaration is identical to
char arr2[] = { 'H', 'e', 'l', 'l', 'o' };
as well as
char arr3[] = { 'H', 'e', 'l', 'l', 'o', '\0' };

OTOH,
char *str1 = "Hello";
defines str1 with type 'pointer to char' and initializes it
to point to an object with type 'array of char' with length
6 whose elements are initialized with a character string literal.
If an attempt is made to use p to modify the contents of the array,
the behavior is undefined.

[Default User]

ju**********@ya hoo.co.in wrote:

char arr2[] = { 'H', 'e', 'l', 'l', 'o' };

This case has no string literal, in fact no string at all. It's an
array of five characters without a null terminator.


Brian

[Mark]

"Default User" <de***********@ yahoo.com> wrote in message
news:3l******** *****@individua l.net...

ju**********@ya hoo.co.in wrote:

char arr2[] = { 'H', 'e', 'l', 'l', 'o' };

This case has no string literal, in fact no string at all. It's an
array of five characters without a null terminator.

No, it's an array of six characters and it DOES have a null terminator.

[Kevin J. Phillips]

Mark wrote:

char arr2[] = { 'H', 'e', 'l', 'l', 'o' };

This case has no string literal, in fact no string at all. It's an
array of five characters without a null terminator.

No, it's an array of six characters and it DOES have a null terminator.

% cat foo.c
#include <stdio.h>

int main(void)
{
char foo[] = { 'H', 'e', 'l', 'l', 'o' };

printf("%u\n", (unsigned)(size of foo));
return 0;
}
% gcc -Wall -ansi -pedantic foo.c
% ./a.out
5

[Default User]

Mark wrote:

"Default User" <de***********@ yahoo.com> wrote in message
news:3l******** *****@individua l.net...

ju**********@ya hoo.co.in wrote:

char arr2[] = { 'H', 'e', 'l', 'l', 'o' };

This case has no string literal, in fact no string at all. It's an
array of five characters without a null terminator.

No, it's an array of six characters and it DOES have a null
terminator.

Wanna bet?

Brian

[Mark McIntyre]

On 9 Aug 2005 02:09:27 -0700, in comp.lang.c ,
ju**********@ya hoo.co.in wrote:

char *str1 = "Hello";
you can modify str1 (change where it points) but not what it currently
points to.
char arr1[] = { "Hello" };
char arr2[] = { 'H', 'e', 'l', 'l', 'o' };

These are identical objects. You can modify what is inside them, but
not change arr1 or arr2.
--
Mark McIntyre
CLC FAQ <http://www.eskimo.com/~scs/C-faq/top.html>
CLC readme: <http://www.ungerhu.com/jxh/clc.welcome.txt >

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[Eric Sosman]

Mark McIntyre wrote:

On 9 Aug 2005 02:09:27 -0700, in comp.lang.c ,
ju**********@ya hoo.co.in wrote:

char *str1 = "Hello";

you can modify str1 (change where it points) but not what it currently
points to.

char arr1[] = { "Hello" };
char arr2[] = { 'H', 'e', 'l', 'l', 'o' };

These are identical objects. [...]

To quote Default User, elsethread: "Wanna bet?"

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