Different ways of declaring strings

[bintom]

What are the differences between the following methods of declaring
strings?

char string1[20] = "C++ forum";
char* string2 = "C++ forum";

I know that the first uses the array notation, whereas the second uses
pointer notation. But apart from that what are the implications /
dangers, etc. if any.

 

[Gennaro Prota]

What are the differences between the following methods of declaring
strings?

char string1[20] = "C++ forum";
char* string2 = "C++ forum";

I know that the first uses the array notation, whereas the second uses
pointer notation. But apart from that what are the implications /
dangers, etc. if any.

It's not just notation: string1 is an array of chars, while string2 is a
pointer to char. A string-literal, such as "C++ forum", denotes an
object of static duration. For this reason there's no danger in writing
e.g.:

char const * f()
{
return "something" ;
}

but the following is a recipe for disaster:

char const * f()
{
char const arr[] = "something" ;
return arr ; // DON'T DO THIS!
}

In your first example you use the static duration object just as a
source to initialize string1 (in fact, it is likely that the compiler
will optimize away that source), whereas in the second one you directly
point to it (its first character, actually; and it may be the same
string literal object of the first line, or not; the implementation must
document this). Since attempting to modify the object corresponding to a
string literal yields undefined behavior you should add const:

char const * string2 = "C++ forum" ;

Omitting the const is allowed for backward-compatibility but deprecated.
Of course, you can modify string1, instead.

 

[Maxim Yegorushkin]

What are the differences between the following methods of declaring
strings?

char string1[20] = "C++ forum";
char* string2 = "C++ forum";

I know that the first uses the array notation, whereas the second uses
pointer notation. But apart from that what are the implications /
dangers, etc. if any.

In the first case there is one object: an (initialised) array.

In the second case there are two objects: a string literal (which is a
char const[] array) and a pointer to it.

 

[Hendrik Schober]

What are the differences between the following methods of declaring
strings?

char string1[20] = "C++ forum";
char* string2 = "C++ forum";

<nitpick1>
This /defines/ strings.

[...]
1. size of string1 is 20, so as Gennaro mentioned the 10 last array
elements fill with null character, but the size of *string2 is 10.

<nitpick2>
The size of '*string2' is 1 (as it points to a 'char'). The size
of 'string2', OTOH, is the size of a 'char*' (4 on my system).

[...]
Saeed Amrollahi

Schobi

 

[Saeed Amrollahi]

What are the differences between the following methods of declaring
strings?
char string1[20] = "C++ forum";
char* string2 = "C++ forum";

  <nitpick1>
  This /defines/ strings.

[...]
1. size of string1 is 20, so as Gennaro mentioned the 10 last array
elements fill with null character, but the size of *string2 is 10.

  <nitpick2>
  The size of '*string2' is 1 (as it points to a 'char'). The size
  of 'string2', OTOH, is the size of a 'char*' (4 on my system).

[...]
  Saeed Amrollahi

  Schobi

Sorry for some confusion. I mean in array case the size of string1 is
20, but in pointer case the size of
string literal which string2 points is 10 (9 bytes for "C++ forum" and
an additional byte
for '\0')

- Saeed Amrollahi

 

[James Kanze]

What are the differences between the following methods of
declaring strings?

char string1[20] = "C++ forum";

This declares an array of char, initialized with
{
'C', '+', '+', ' ', 'f',
'o', 'r', 'u', 'm', '\0',
'\0', '\0', '\0', '\0', '\0',
'\0', '\0', '\0', '\0', '\0'
} ;

char* string2 = "C++ forum";

This is really incorrect, and requires a deprecated conversion
in order for it to compile. It's the equivalent of declaring a
static char const hidden[ 10 ] =
{
'C', '+', '+', ' ', 'f',
'o', 'r', 'u', 'm', '\0'
} ;
and initializing string2 with its address.

Neither are used to declare "strings" in C++; one defines an
array of char, and the other a pointer to char. To declare a
string:
std::string string1( "C++ forum" ) ;
..

I know that the first uses the array notation, whereas the
second uses pointer notation. But apart from that what are the
implications / dangers, etc. if any.

The implication is that they are two very different statements,
declaring different types of objects.

 

[Gennaro Prota]

What are the differences between the following methods of
declaring strings?

char string1[20] = "C++ forum";

This declares an array of char, initialized with
{
'C', '+', '+', ' ', 'f',
'o', 'r', 'u', 'm', '\0',
'\0', '\0', '\0', '\0', '\0',
'\0', '\0', '\0', '\0', '\0'
} ;

Adding some historical information (usually a special quality of
yours, the fact that the last elements are initialized to zero was
clarified with C90's TC2.

<http://www.open-std.org/jtc1/sc22/wg14/www/docs/tc2.htm>

(the fix to subclause 6.5.7). C++03 isn't in sync (i.e., it leaves the
case as uncertain as the original ISO C did) and, last time I checked,
the working draft isn't, either.