lifetime of char[]?

[Stefan Ram]

In the following example:

{ const char * concat =( stdstring + stdstring_ ).c_str(); ... }

it seems that the value of c_str() is a pointer to a
temporary char array. Now, that POINTER is used to
initialize the variable »concat«.

There might be a rule that a temporary can be used to
initialize an object with automatic storage duration, and
then the lifetime of that temporary is extended to the
lifetime of that automatic object.

But what about the temporary char ARRAY pointed to by the
pointer »concat«? Is there a rule that extends its lifetime
too? After all, it is not the same as the POINTER to it,
so another rule would be needed to extend its lifetime too.

So, can »concat« safely (portably) be dereferenced in this
block to get access to the concatenation of the C++-strings
as a C-string?

 

[Melzzzzz]

On 9 Nov 2013 01:18:25 GMT

In the following example:

{ const char * concat =( stdstring + stdstring_ ).c_str(); ... }


So, can »concat« safely (portably) be dereferenced in this
block to get access to the concatenation of the C++-strings
as a C-string?

No.

 

[Öö Tiib]

In the following example:

{ const char * concat =( stdstring + stdstring_ ).c_str(); ... }

it seems that the value of c_str() is a pointer to a
temporary char array. Now, that POINTER is used to
initialize the variable »concat«.

Yes, and pointlessly so. Smart enough tool could warn. It is
useless pointer on very next line. That works:

{
std::string& ref =( stdstring + stdstring_ );
const char* concat = ref.c_str();
// ...
} // <- ref is valid until here and so is concat

But generally ... avoid raw pointers.

 

[Alf P. Steinbach]

Yes, and pointlessly so. Smart enough tool could warn. It is
useless pointer on very next line. That works:

{
std::string& ref =( stdstring + stdstring_ );
const char* concat = ref.c_str();
// ...
} // <- ref is valid until here and so is concat

But generally ... avoid raw pointers.

The above won't compile.

But

"std::string const&"

or

"std::string&&"

would.

The easiest and safest solution is to store the concatenation result in
a std::string, since that's the string class used in the code.


Cheers,

- Alf (nitpicking)

 

[Öö Tiib]

That is wrong Mr Homophobic Bigot; it needs to be reference to const.

Thanks for correcting, Mr Foulmouthed Fagot, that was a typo. OP
needed const but I mistyped it somehow.