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deepak.sethi@gmail.com
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 Posted: Tue Aug 16, 2005 2:35 pm Post subject: Specifying Initial bucket size in hash_map |
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I am interested in specifying the Initial bucket size for hash_map
declared in the class.
There is no member function to do so except the constructor.
For eg
Class A
{
hash_map <int,string> h;
}
The default size is 100 and i want to create "h" with a initial size
1000.
I cannot use
"hash_map <int,string> h(100);" in the .h file as this is static
initialization.
Do i have to use the Constructor of class A or is there any other way.
Kindly provide psuedo-code
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mlimber
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| Posted: Wed Aug 17, 2005 8:53 am Post subject: Re: Specifying Initial bucket size in hash_map |
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[email]deepak.sethi (AT) gmail (DOT) com[/email] wrote:
| Quote: | I am interested in specifying the Initial bucket size for hash_map
declared in the class.
There is no member function to do so except the constructor.
For eg
Class A
{
hash_map <int,string> h;
}
The default size is 100 and i want to create "h" with a initial size
1000.
I cannot use
"hash_map <int,string> h(100);" in the .h file as this is static
initialization.
Do i have to use the Constructor of class A or is there any other way.
Kindly provide psuedo-code
|
You need to use the constructor to initialize members. You can use the
member initialization list like this:
class A
{
public:
A( size_t bucketSize = 1000 )
: h( bucketSize )
{}
private:
hash_map <int,string> h;
}
Cheers! --M
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jrm
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| Posted: Wed Aug 17, 2005 8:55 am Post subject: Re: Specifying Initial bucket size in hash_map |
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You can initialize h in A's ctor:
class A
{
public:
A() :
h(1000)
{
}
size_t foo() const { return h.bucket_count(); }
private:
hash_map<int, string> h;
};
int main()
{
A a;
cout<
return 0;
}
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Ali Çehreli
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| Posted: Thu Aug 18, 2005 1:06 pm Post subject: Re: Specifying Initial bucket size in hash_map |
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<deepak.sethi (AT) gmail (DOT) com> wrote
| Quote: | I am interested in specifying the Initial bucket size for hash_map
declared in the class.
There is no member function to do so except the constructor.
|
That means that you have to provide the bucket size at construction time.
| Quote: | For eg
Class A
{
hash_map <int,string> h;
}
The default size is 100 and i want to create "h" with a initial size
1000.
I cannot use
"hash_map <int,string> h(100);" in the .h file as this is static
initialization.
Do i have to use the Constructor of class A or is there any other way.
|
Since h is constructed during the construction of A, and you have to provide
the size at that time, that would be the best time :)
A::A()
:
h(100)
{}
Another method would be to use a member function to initialize h:
void A::initialize_h(int size)
{
h = hash_map<int, string>(size);
}
Since the above clears the contents of h, you may want to copy the contents
to a temporary hash_map of size 'size' before doing the assignment. Also
renaming the function to 'resize_h':
void A::resize_h(int size)
{
hash_map<int, string> new_h(size);
// copy the old contents to new_h here
// (Your hash_map may have a constructor to achieve this.)
h = new_h;
}
Ali
[ See http://www.gotw.ca/resources/clcm.htm for info about ]
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