2d arrays!

[raashid bhatt]

#include <stdio.h>

int main(int argc, char **argv)
{

char i[][10] = {"welcome", "nelcome"};
// pointer to the array of chars
char (*p)[] = {"Welcoem", "welcome"}; //dosent work

// array of pointer to chars
char *s[] = {"welcome", "welcome"}; // works strange!
return 0;
}

[John Bode]

On Aug 21, 8:53 am, raashid bhatt <[e-mail]:

#include <stdio.h>

int main(int argc, char **argv)
{

char i[][10] = {"welcome", "nelcome"};
// pointer to the array of chars
char (*p)[] = {"Welcoem", "welcome"}; //dosent work

p is a pointer to an array; as such, it is expecting an array address,
not 2-d array initializer.

What you're looking for is something like this:

char (*p)[] = &"Welcome"; // note the presence of the & operator

Alternately, something like this:

char a[] = "Welcome";
char (*p)[] = &a;

// array of pointer to chars
char *s[] = {"welcome", "welcome"}; // works strange!

String literals are stored as arrays of char; if a string literal
appears anywhere other than as an operator to & or sizeof, the usual
array conversions come into play (i.e., the reference to the string is
converted to type char*, and the value of the reference is set to
point to the first character in the string).

So your initializer can be seen as two objects of type char*.

return 0;

}

You really, really, *REALLY* need to get a good C reference manual,
because you've been asking some very basic questions that are best
answered by such a reference. My main reference is Harbison &
Steele's "C: A Reference Manual" (currently 5th edition). Whatever
you get, go there *first*, and if something still doesn't make sense,
feel free to ask here.

[raashid bhatt]

feel free to ask here.

Thanks a lot Man at last u understood my prob

[jameskuyper]

John Bode wrote:

On Aug 21, 8:53 am, raashid bhatt <[e-mail]:

....

char (*p)[] = {"Welcoem", "welcome"}; //dosent work

p is a pointer to an array; as such, it is expecting an array address,
not 2-d array initializer.

What you're looking for is something like this:

char (*p)[] = &"Welcome"; // note the presence of the & operator

I doubt that he's looking for code which violates a constraint. The
operand of & must be an lvalue.

[jameskuyper]

raashid bhatt wrote:

#include <stdio.h>

int main(int argc, char **argv)
{

char i[][10] = {"welcome", "nelcome"};
// pointer to the array of chars
char (*p)[] = {"Welcoem", "welcome"}; //dosent work

// array of pointer to chars
char *s[] = {"welcome", "welcome"}; // works strange!
return 0;
}

John Bode has already discussed why 'p' doesn't work. However, it
would still be helpful if you could show us what you want to do with
these objects.

I would strongly recommend declaring 's' as "const char*s[]", because
the memory its elements point at is memory you cannot safely write to.
Declaring it 'const' will make most attempts to mis-use it into errors
that the compiler can warn you about. So long as you don't need to
write to that memory, I'd recommend using 's'. Therefore, I'm curious
about why you think that it "works strange!". Could you give an
example of what's strange about the way it works?

If you need to be able to change the contents of the strings you're
working with, I'd recommend using 'i'. However, there are situations
where you might want to also define the following:

char *i_ptr[] = {&i[0], &i[1]};

[Harald van =?UTF-8?b?RMSzaw==?=]

On Thu, 21 Aug 2008 12:12:11 -0700, jameskuyper wrote:

John Bode wrote:

>What you're looking for is something like this:

char (*p)[] = &"Welcome"; // note the presence of the & operator

I doubt that he's looking for code which violates a constraint. The
operand of & must be an lvalue.

String literals are lvalues. 6.5.1p4: "A string literal is a primary
expression. It is an lvalue with type as detailed in 6.4.5."

Interestingly, at least one compiler agrees with you, though:

test.c:2: Error: Address-of operator applied to something that is not an
lvalue
char (*p)[] = &"Welcome";
^ here

I should probably go and report that as a bug.

[jameskuyper]

Harald van D©¦k wrote:

On Thu, 21 Aug 2008 12:12:11 -0700, jameskuyper wrote:

John Bode wrote:

What you're looking for is something like this:

char (*p)[] = &"Welcome"; // note the presence of the & operator

I doubt that he's looking for code which violates a constraint. The
operand of & must be an lvalue.

String literals are lvalues. 6.5.1p4: "A string literal is a primary
expression. It is an lvalue with type as detailed in 6.4.5."

Interestingly, at least one compiler agrees with you, though:

test.c:2: Error: Address-of operator applied to something that is not an
lvalue
char (*p)[] = &"Welcome";
^ here

You're right - after drilling Raashid on the fact that there are three
situations in which lvalues with array type are not automatically
converted into pointers to the first element, I should have remembered
that string literals are the third exception. It's not an exception
that comes up very often, in my experience.

[pete]

ja*********@verizon.net wrote:

Harald van D©¦k wrote:

>On Thu, 21 Aug 2008 12:12:11 -0700, jameskuyper wrote:

>>John Bode wrote:
What you're looking for is something like this:

char (*p)[] = &"Welcome"; // note the presence of the & operator
I doubt that he's looking for code which violates a constraint. The
operand of & must be an lvalue.

String literals are lvalues. 6.5.1p4: "A string literal is a primary
expression. It is an lvalue with type as detailed in 6.4.5."

Interestingly, at least one compiler agrees with you, though:

test.c:2: Error: Address-of operator applied to something that is not an
lvalue
char (*p)[] = &"Welcome";
^ here

You're right - after drilling Raashid on the fact that there are three
situations in which lvalues with array type are not automatically
converted into pointers to the first element, I should have remembered
that string literals are the third exception. It's not an exception
that comes up very often, in my experience.

You're wrong again.

It's the address operator that is suppressing the conversion.

The special rule for string literals,
is when they are initializers for an array,
as in:

char array[] = "Welcome";

--
pete