char *a="this is a string";
char a[]="this is a string";
first is a pointer while second is an array.Tell me more differences
char a[]="this is a string";
first is a pointer while second is an array.Tell me more differences
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Re: plz tell me the difference
"jeniffer" <zenith.of.perf ection@gmail.co m> wrote in message
news:1146211433 .676652.125630@ j33g2000cwa.goo glegroups.com.. .[color=blue]
> char *a="this is a string";
> char a[]="this is a string";
> first is a pointer while second is an array.Tell me more differences
>[/color]
Questions 1.32 and 6.2 and their answers should help. If not, tell us why
not.
Rod Pemberton
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Re: plz tell me the difference
char *a declares a pointer to a string. So, to say char *a = "this is
a string", puts the address of the first letter of the string into the
pointer a. So, that first "t" is located somewhere in memory, the
pointer a contains the address.
[color=blue]
> char *a="this is a string";[/color]
If you wrote printf("char = %d",a); you would see the address
where a has been stored
If you wrote printf("char = %c",*a); you would see what value was
at that address.
flank
Comment
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Re: plz tell me the difference
"char *a="this is a string"
Here the string literals " this is a string " is stored in data
segment & you are making pointer variable "a" to point this location
but "a" can be changed to point to any other location in a program.
char a[]="this is a string";
but here you can't change pointer of the variable "a" to other
location in the program.
i hope this help you....
jeniffer wrote:[color=blue]
> char *a="this is a string";
> char a[]="this is a string";
> first is a pointer while second is an array.Tell me more differences[/color]
Comment
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Re: plz tell me the difference
"char *a="this is a string"
Here the string literals " this is a string " is stored in data
segment & you are making pointer variable "a" to point this location
but "a" can be changed to point to any other location in a program.
char a[]="this is a string";
but here you can't change pointer of the variable "a" to other
location in the program.
i hope this help you....
jeniffer wrote:[color=blue]
> char *a="this is a string";
> char a[]="this is a string";
> first is a pointer while second is an array.Tell me more differences[/color]
Comment
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Re: plz tell me the difference
AG opined:
[color=blue]
> char *a declares a pointer to a string. So, to say char *a = "this
> is a string", puts the address of the first letter of the string into
> the pointer a. So, that first "t" is located somewhere in memory,
> the pointer a contains the address.[/color]
So far so good, albeit somewhat less than precise...
[color=blue][color=green]
>> char *a="this is a string";[/color]
> If you wrote printf("char = %d",a); you would see the address
> where a has been stored[/color]
No, you wouldn't.
You'd see (if you're lucky) whatever your implementation thinks a
pointer interpreted as an `int` looks like. In fact, you get Undefined
Behaviour, as "%d" tells `printf()` to expect an `int`, when in fact
you're passing `char *`. UB essentially means: all bets are off, duck
or grouse!
Also, since you didn't terminate output with '\n', you may end up
getting absolutely no output at all.
You could output a pointer (as represented by your implementation) if
you used "%p" instead. How, and whether it relates to memory
addresses, is another matter.
[color=blue]
> If you wrote printf("char = %c",*a); you would see what value
> was at that address.[/color]
This will work as expected, yes (apart from missing '\n', that is).
--
The trouble with a kitten is that
When it grows up, it's always a cat
-- Ogden Nash.
<http://clc-wiki.net/wiki/Introduction_to _comp.lang.c>
Comment
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Re: plz tell me the difference
code break opined:
[color=blue]
>
> "char *a="this is a string"
> Here the string literals " this is a string " is stored in data
> segment & you are making pointer variable "a" to point this location
> but "a" can be changed to point to any other location in a program.[/color]
C knows not of "data segment", nor does it say where exactly the string
is stored. It's important to note that you're not allow to modify it.
[color=blue]
> char a[]="this is a string";
>
> but here you can't change pointer of the variable "a" to other
> location in the program.[/color]
Wrong.
In this case `a` is not a pointer, but an array. It is correct that you
can't make `a` refer to something else, but that is true of any
variable you declare. As it is not declared `const` the contents of
this array can be modified.
Also, in the line above, the string is used to initialise array `a`
(including the terminating '\0'). It is not otherwise accessible from
the program.
[color=blue]
> i hope this help you....[/color]
Actually, no.
--
He's dead, Jim
-- McCoy, "The Devil in the Dark", stardate 3196.1
<http://clc-wiki.net/wiki/Introduction_to _comp.lang.c>
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Re: plz tell me the difference
jeniffer wrote:[color=blue]
> char *a="this is a string";
> char a[]="this is a string";
> first is a pointer while second is an array.Tell me more differences[/color]
I'm going to rewrite this a little:
char *ptr="this is a string";
char arr[]="this is a string";
In the above code, we're talking about 3 distinct objects: the string
literal "this is a string", the pointer ptr, and the array arr. The
following hypothetical memory map shows the state of each object after
initialization (best viewed with a fixed-size font):
Item Address Contents
---- ------- --------
literal 0x0800 "this is a string"
ptr 0x1000 0x0800
arr 0x2000 "this is a string"
The string literal has its own address in memory, and may not be
writable (i.e., you may not be allowed to write to the bytes between
0x0800 and 0x0811; assume that you can't).
The pointer ptr contains the address of the string literal. Since the
literal may not be writable, you may not write to *ptr or ptr[n];
however, you can assign a new value to ptr (i.e., ptr=NULL,
ptr=&arr[0], ptr=malloc(16), etc.), and if this new value points to
writable memory, you may then also write to *ptr or ptr[n].
The array arr contains a *copy* of the contents of the string literal.
The array contents are writable, so you can write to *arr or arr[n];
however, the array object itself is not writable, so you may not write
arr=NULL, or arr="this is a string", or arr=p, etc.
Comment
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Re: plz tell me the difference
"AG" <andrewkgentile @gmail.com> writes:[color=blue]
> char *a declares a pointer to a string. So, to say char *a = "this is
> a string", puts the address of the first letter of the string into the
> pointer a. So, that first "t" is located somewhere in memory, the
> pointer a contains the address.[/color]
Strictly speaking, char *a declares a pointer to a char, not a pointer
to a string. That pointer-to-char can, and commonly does, point to
the first character of a string (a sequence of chars terminated by a
'\0'), and can be used to access the entire string. Referring to a as
a "pointer to a string" is a common verbal shorthand, and a useful
one, but it's not literally correct.
More generally, it's common to use a pointer-to-FOO to point to the
first element of an array of FOO:
FOO arr[10];
FOO *ptr = arr; /* or, equivalently, FOO *ptr = &arr[0]; */
but it's *also* possible to have a pointer to an array, which is
distinct from a pointer to the array's first element:
FOO (*arr_ptr)[10] = &arr;
Calling ptr a "pointer to an array" blurs this distinction.
Incidentally, pointers to arrays are rarely useful. It's usually more
useful to have a pointer to the first element of an array, and keep
track of the length separately rather than hard-wiring a fixed length
into an pointer-to-array type.
--
Keith Thompson (The_Other_Keit h) kst-u@mib.org <http://www.ghoti.net/~kst>
San Diego Supercomputer Center <*> <http://users.sdsc.edu/~kst>
We must do something. This is something. Therefore, we must do this.
Comment
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Re: plz tell me the difference
Keith Thompson wrote:[color=blue]
>
> "AG" <andrewkgentile @gmail.com> writes:[color=green]
> > char *a declares a pointer to a string.
> > So, to say char *a = "this is a string",
> > puts the address of the first letter of the string into the
> > pointer a. So, that first "t" is located somewhere in memory, the
> > pointer a contains the address.[/color]
>
> Strictly speaking, char *a declares a pointer to a char, not a pointer
> to a string. That pointer-to-char can, and commonly does, point to
> the first character of a string (a sequence of chars terminated by a
> '\0'), and can be used to access the entire string. Referring to a as
> a "pointer to a string" is a common verbal shorthand, and a useful
> one, but it's not literally correct.[/color]
(a) is a "pointer to a string" according to the definition
in the standard for "pointer to a string".
I don't think it would be wrong to say that
char *a = "this is a string";
declares a pointer with a value unequal to NULL.
The point being, that there are other aspects
to an initialised declaration, besides the type.
--
pete
Comment
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Re: plz tell me the difference
pete <pfiland@mindsp ring.com> writes:[color=blue]
> Keith Thompson wrote:[color=green]
>> "AG" <andrewkgentile @gmail.com> writes:[color=darkred]
>> > char *a declares a pointer to a string.
>> > So, to say char *a = "this is a string",
>> > puts the address of the first letter of the string into the
>> > pointer a. So, that first "t" is located somewhere in memory, the
>> > pointer a contains the address.[/color]
>>
>> Strictly speaking, char *a declares a pointer to a char, not a pointer
>> to a string. That pointer-to-char can, and commonly does, point to
>> the first character of a string (a sequence of chars terminated by a
>> '\0'), and can be used to access the entire string. Referring to a as
>> a "pointer to a string" is a common verbal shorthand, and a useful
>> one, but it's not literally correct.[/color]
>
> (a) is a "pointer to a string" according to the definition
> in the standard for "pointer to a string".[/color]
You're right. C99 7.1.1 says:
A _pointer to a string_ is a pointer to its initial (lowest
addressed) character.
If you interpret the phrase literally, it's a useful shorthand but not
strictly correct. Since the standard provides a definition for it, I
concede the point.
--
Keith Thompson (The_Other_Keit h) kst-u@mib.org <http://www.ghoti.net/~kst>
San Diego Supercomputer Center <*> <http://users.sdsc.edu/~kst>
We must do something. This is something. Therefore, we must do this.
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