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Jakob Bieling
Guest
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 Posted: Sat Feb 28, 2004 4:17 pm Post subject: Q: Using an extern const size_t? |
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Hi,
I have the following scenario:
--- file1.cpp ---
size_t const array_size = 10;
--- end file1.cpp ---
--- file2.cpp ---
class test
{
int m_nums [array_size];
};
--- end file2.cpp ---
My compiler, VC++7.1, complains about not having a constant expression
for the array. Why can the array size not be 'calculated' at compile-time?
Or is it just a bug in VC++?
Thanks!
--
jb
(replace y with x if you want to reply by e-mail)
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Jakob Bieling
Guest
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| Posted: Sat Feb 28, 2004 4:21 pm Post subject: Re: Using an extern const size_t? |
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"Jakob Bieling" <netsurf (AT) gmy (DOT) net> wrote
I forgot a line:
--- file1.cpp ---
size_t const array_size = 10;
--- end file1.cpp ---
--- file2.cpp ---
extern size_t const array_size;
class test
{
int m_nums [array_size];
};
--- end file2.cpp ---
Sorry about that
--
jb
(replace y with x if you want to reply by e-mail)
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John Harrison
Guest
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| Posted: Sat Feb 28, 2004 4:22 pm Post subject: Re: Using an extern const size_t? |
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"Jakob Bieling" <netsurf (AT) gmy (DOT) net> wrote
| Quote: | Hi,
I have the following scenario:
--- file1.cpp ---
size_t const array_size = 10;
--- end file1.cpp ---
--- file2.cpp ---
|
I guessing that you missed out
extern const size_t array_size;
here.
| Quote: | class test
{
int m_nums [array_size];
};
--- end file2.cpp ---
My compiler, VC++7.1, complains about not having a constant expression
for the array. Why can the array size not be 'calculated' at compile-time?
Or is it just a bug in VC++?
|
Put
size_t const array_size = 10;
in a header file and include that header file in file1.cpp and file2.cpp.
This is OK because in C++ constants have internal linkage by default so you
won't get an error about array_size being declared twice.
john
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Jakob Bieling
Guest
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| Posted: Sat Feb 28, 2004 4:29 pm Post subject: Re: Using an extern const size_t? |
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"John Harrison" <john_andronicus (AT) hotmail (DOT) com> wrote
| Quote: |
"Jakob Bieling" <netsurf (AT) gmy (DOT) net> wrote in message
news:c1qeta$ig9$00$1 (AT) news (DOT) t-online.com...
Hi,
I have the following scenario:
--- file1.cpp ---
size_t const array_size = 10;
--- end file1.cpp ---
--- file2.cpp ---
I guessing that you missed out
extern const size_t array_size;
here.
|
Yes, see my reply to myself ;)
| Quote: | class test
{
int m_nums [array_size];
};
--- end file2.cpp ---
My compiler, VC++7.1, complains about not having a constant
expression
for the array. Why can the array size not be 'calculated' at
compile-time?
Or is it just a bug in VC++?
Put
size_t const array_size = 10;
in a header file and include that header file in file1.cpp and file2.cpp.
This is OK because in C++ constants have internal linkage by default so
you
won't get an error about array_size being declared twice.
|
Right, but why does the above example not work? Theoretically, it
should, or what am I missing?
--
jb
(replace y with x if you want to reply by e-mail)
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Artie Gold
Guest
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| Posted: Sat Feb 28, 2004 5:47 pm Post subject: Re: Using an extern const size_t? |
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Jakob Bieling wrote:
| Quote: | "John Harrison" <john_andronicus (AT) hotmail (DOT) com> wrote in message
news:c1qf7i$1m1avc$1 (AT) ID-196037 (DOT) news.uni-berlin.de...
"Jakob Bieling" <netsurf (AT) gmy (DOT) net> wrote in message
news:c1qeta$ig9$00$1 (AT) news (DOT) t-online.com...
Hi,
I have the following scenario:
--- file1.cpp ---
size_t const array_size = 10;
--- end file1.cpp ---
--- file2.cpp ---
I guessing that you missed out
extern const size_t array_size;
here.
Yes, see my reply to myself ;)
class test
{
int m_nums [array_size];
};
--- end file2.cpp ---
My compiler, VC++7.1, complains about not having a constant
expression
for the array. Why can the array size not be 'calculated' at
compile-time?
Or is it just a bug in VC++?
Put
size_t const array_size = 10;
in a header file and include that header file in file1.cpp and file2.cpp.
This is OK because in C++ constants have internal linkage by default so
you
won't get an error about array_size being declared twice.
Right, but why does the above example not work? Theoretically, it
should, or what am I missing?
|
You are missing the fact that the value of `array_size' will not be
known until link time (as it is defined in a different translation unit).
HTH,
--ag
--
Artie Gold -- Austin, Texas
"Yeah. It's an urban legend. But it's a *great* urban legend!"
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Jakob Bieling
Guest
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| Posted: Sat Feb 28, 2004 6:05 pm Post subject: Re: Using an extern const size_t? |
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"Artie Gold" <artiegold (AT) austin (DOT) rr.com> wrote
| Quote: | --- file1.cpp ---
size_t const array_size = 10;
--- end file1.cpp ---
--- file2.cpp ---
extern const size_t array_size;
class test
{
int m_nums [array_size];
};
--- end file2.cpp ---
Right, but why does the above example not work? Theoretically, it
should, or what am I missing?
You are missing the fact that the value of `array_size' will not be
known until link time (as it is defined in a different translation unit).
|
Oh .. makes sense now, yes!
Thanks!
--
jb
(replace y with x if you want to reply by e-mail)
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