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Jason
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 Posted: Wed Oct 19, 2005 8:49 am Post subject: const string & and static char array |
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Hi,
I didn't understand how come I can call Foo::m1 with a static
char[] parameter. I am using Visual C++ 6.0 and never tried this on
another compiler. Is this a compiler bug?
class Foo
{
public:
void m1(const string& str);
};
class Settings
{
public:
static char Setting1[256];
};
// in the code
Foo foo;
foo.m1(Settings::Setting1); // why there is no error? is there an
implicit conversion?
Jason
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Allan W
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| Posted: Thu Oct 20, 2005 11:14 am Post subject: Re: const string & and static char array |
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Jason wrote:
| Quote: | class Foo {
public:
void m1(const string& str);
};
class Settings {
public:
static char Setting1[256];
};
// in the code
Foo foo;
foo.m1(Settings::Setting1); // why there is no error?
// is there an implicit conversion?
|
Yes. See the standard, 21.3.1/5 -- one of the constructors of
string is:
basic_string(const charT* s, const Allocator&A = Allocator());
So your character array is converted to a char* for the first
parameter, and the string's default allocator is being used as
the second.
Why does that surprise you?
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Sebastian Redl
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| Posted: Thu Oct 20, 2005 11:21 am Post subject: Re: const string & and static char array |
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Jason wrote:
| Quote: | // in the code
Foo foo;
foo.m1(Settings::Setting1); // why there is no error? is there an
implicit conversion?
|
There is. char[] is implicitely converted to const char *. std::string has a
constructor that takes a const char *, which is used as a conversion
constructor to construct a temporary std::string object that the reference
gets bound to.
--
Sebastian Redl
[ See http://www.gotw.ca/resources/clcm.htm for info about ]
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Ben Hutchings
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| Posted: Thu Oct 20, 2005 12:06 pm Post subject: Re: const string & and static char array |
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Jason <bumperman_jc (AT) hotmail (DOT) com> wrote:
| Quote: | Hi,
I didn't understand how come I can call Foo::m1 with a static
char[] parameter. I am using Visual C++ 6.0 and never tried this on
another compiler. Is this a compiler bug?
|
It's not a bug.
| Quote: | class Foo
{
public:
void m1(const string& str);
};
class Settings
{
public:
static char Setting1[256];
};
// in the code
Foo foo;
foo.m1(Settings::Setting1); // why there is no error? is there an
// implicit conversion?
|
There are built-in implicit conversions from char[n] (for any size n)
to char * and from char * to const char *, and std::string has a
constructor that takes const char * and isn't declared explicit. So
there is an implicit conversion from char[256] to std::string.
--
Ben Hutchings
Having problems with C++ templates? Your questions may be answered by
<http://womble.decadentplace.org.uk/c++/template-faq.html>.
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unspammable@gmail.com
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| Posted: Thu Oct 20, 2005 12:56 pm Post subject: Re: const string & and static char array |
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std::string has a copy constructor that accepts a char pointer.
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Jack Klein
Guest
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| Posted: Thu Oct 20, 2005 1:57 pm Post subject: Re: const string & and static char array |
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On 19 Oct 2005 04:49:30 -0400, "Jason" <bumperman_jc (AT) hotmail (DOT) com>
wrote in comp.lang.c++.moderated:
| Quote: | Hi,
I didn't understand how come I can call Foo::m1 with a static
char[] parameter. I am using Visual C++ 6.0 and never tried this on
another compiler. Is this a compiler bug?
class Foo
{
public:
void m1(const string& str);
};
class Settings
{
public:
static char Setting1[256];
};
// in the code
Foo foo;
foo.m1(Settings::Setting1); // why there is no error? is there an
implicit conversion?
Jason
|
There is a constructor for std::string that accepts a C string as a
source parameter. This constructor is being invoked to create a
temporary std::string, which is bound to the constant reference for
the duration of the function call, and destroyed when the function
returns.
--
Jack Klein
Home: http://JK-Technology.Com
FAQs for
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Carlos Moreno
Guest
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| Posted: Thu Oct 20, 2005 7:36 pm Post subject: Re: const string & and static char array |
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[email]unspammable (AT) gmail (DOT) com[/email] wrote:
| Quote: | std::string has a copy constructor that accepts a char pointer.
|
No it doesn't.
If it accepts a char pointer, then it is *not* a copy constructor.
Carlos
--
[ See http://www.gotw.ca/resources/clcm.htm for info about ]
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