Defining a variable in switch statement

[Rahul]

Hi,
Is the following correct? Here i have declaread a char array in case 1:
and am using the same in case 2:
first I tried another definition of ch in case 2: assuming that if i=2
then char ch[] will not get allocated in case 1:. But the compiler gave
me (re-definition error) so i removed it and now its working fine.
Is it correct as per the standard?

switch (i)
{
case 1:
char ch[12];
strcpy(ch, "case 1\n");
cout<<ch;
break;
case 2:
strcpy(ch, "case 2\n"); //Can i use it here, when i=2, why
should the compiler allocate
// the variable shich is
declared in the case which is not true.
cout<<ch;
break;

default:
strcpy(ch, "default\n"); // Is it ok here also?
cout<<ch;
}

 

[Forest]

You can use { and } to meet your requirement.

[example]

switch ( i )
{
case 1:
{
char ch[1];
//...
break;
}
case 2:
{
char ch[2];
//...
break;
}
//...
}

[end example]

 

[Rahul]

You can use { and } to meet your requirement.

[example]

switch ( i )
{
case 1:
{
char ch[1];
//...
break;
}
case 2:
{
char ch[2];
//...
break;
}
//...
}

[end example]

Hi,
Is the following correct? Here i have declaread a char array in case 1:
and am using the same in case 2:
first I tried another definition of ch in case 2: assuming that if i=2
then char ch[] will not get allocated in case 1:. But the compiler gave
me (re-definition error) so i removed it and now its working fine.
Is it correct as per the standard?

switch (i)
{
case 1:
char ch[12];
strcpy(ch, "case 1\n");
cout<<ch;
break;
case 2:
strcpy(ch, "case 2\n"); //Can i use it here, when i=2, why
should the compiler allocate
// the variable shich is
declared in the case which is not true.
cout<<ch;
break;

default:
strcpy(ch, "default\n"); // Is it ok here also?
cout<<ch;
}

That I have done, But I wanted to know is the above behaviour as per
the standards and is guranteed to work always?

 

[Forest]

It is valid I think. You can just consider *case statement* as a
*label*.

You can use { and } to meet your requirement.

[example]

switch ( i )
{
case 1:
{
char ch[1];
//...
break;
}
case 2:
{
char ch[2];
//...
break;
}
//...
}

[end example]

Hi,
Is the following correct? Here i have declaread a char array in case 1:
and am using the same in case 2:
first I tried another definition of ch in case 2: assuming that if i=2
then char ch[] will not get allocated in case 1:. But the compiler gave
me (re-definition error) so i removed it and now its working fine.
Is it correct as per the standard?

switch (i)
{
case 1:
char ch[12];
strcpy(ch, "case 1\n");
cout<<ch;
break;
case 2:
strcpy(ch, "case 2\n"); //Can i use it here, when i=2, why
should the compiler allocate
// the variable shich is
declared in the case which is not true.
cout<<ch;
break;

default:
strcpy(ch, "default\n"); // Is it ok here also?
cout<<ch;
}

That I have done, But I wanted to know is the above behaviour as per
the standards and is guranteed to work always?

 

[Jakob Bieling]

Hi,
Is the following correct? Here i have declaread a char array in case
1: and am using the same in case 2:
first I tried another definition of ch in case 2: assuming that if i=2
then char ch[] will not get allocated in case 1:. But the compiler
gave me (re-definition error) so i removed it and now its working
fine.
Is it correct as per the standard?

Afaik, no. The initialization of 'ch' might be skipped when 'i' is
2.

switch (i)
{
case 1:
char ch[12];
strcpy(ch, "case 1\n");
cout<<ch;
break;
case 2:
strcpy(ch, "case 2\n"); //Can i use it here, when i=2, why
should the compiler allocate
// the variable shich is
declared in the case which is not true.
cout<<ch;
break;

default:
strcpy(ch, "default\n"); // Is it ok here also?
cout<<ch;
}

hth

 

[Jakob Bieling]

You can use { and } to meet your requirement.

Please do not top-post. Always place it below the relevant part of
the message you are replying to. It just makes live easier for most of
us, as we are used to reading articles/books from top to bottom and not
from bottom to top.

regards

 

[Michiel.Salters]

Hi,
Is the following correct? Here i have declaread a char array in case
1: and am using the same in case 2:
first I tried another definition of ch in case 2: assuming that if i=2
then char ch[] will not get allocated in case 1:. But the compiler
gave me (re-definition error) so i removed it and now its working
fine.
Is it correct as per the standard?

Afaik, no. The initialization of 'ch' might be skipped when 'i' is
2.

There is no initialization of 'ch' in the first place. So it's correct,
but similar code which /does/ initialize a variable in case 1 will
have a problem.

HTH,
Michiel Salters

 

[Jakob Bieling]

Jakob Bieling wrote:

switch (i)
{
case 1:
char ch[12];
strcpy(ch, "case 1\n");
cout<<ch;
break;

Afaik, no. The initialization of 'ch' might be skipped when 'i'
is 2.

There is no initialization of 'ch' in the first place. So it's

What about default initialization? The elements of the array need to
be initialized with something, even if it's an unspecified value, no?

regards

 

[Default User]

It is valid I think. You can just consider *case statement* as a
*label*.

Please don't top-post. Your reply belongs following or interspersed
with properly trimmed quotes. See the newsgroup FAQ:
<http://www.parashift.com/c++-faq-lite/how-to-post.html#faq-5.4> or
<http://www.caliburn.nl/topposting.html>



Brian

 

[Default User]

(e-mail address removed) wrote:

What about default initialization? The elements of the array need
to be initialized with something, even if it's an unspecified value,
no?

No, and in fact most automatic variables are not initialized. Using
such a variable is undefined behavior.





Brian

 

[Jakob Bieling]

No, and in fact most automatic variables are not initialized. Using
such a variable is undefined behavior.

True, that I knew. Thanks for pointing it out!

 

[Default User]

No, and in fact most automatic variables are not initialized. Using
such a variable is undefined behavior.

That statement isn't very good. You can do an number of things with
with the variable itself, such as assign to it or take its address. I
should have said using the VALUE of such a variable is undefined
behavior.



Brian