Dear list,
I am using std::vector<boo l> (bit_vector) to store my bit sequence. To
access the same sequence from C (to expose to a python module), I need
to know the pointer and offset of vector::<bool>: :iterator (or
reference). However, given a std::vector<boo l> a, all a.begin(), a[0]
etc are instances of a proxy class so I can not do things like
&*a.begin(). Is there a safe way to get the information I need?
Many thanks in advance.
Bo
8  3540 
* Bo Peng:
I am using std::vector<boo l> (bit_vector) to store my bit sequence. To
access the same sequence from C (to expose to a python module), I need
to know the pointer and offset of vector::<bool>: :iterator (or
reference). However, given a std::vector<boo l> a, all a.begin(), a[0]
etc are instances of a proxy class so I can not do things like
&*a.begin(). Is there a safe way to get the information I need?
Something like
void python( int const bitValues[], int nValues );
void callPython( std::vector<boo l> const& bits )
{
std::vector<int > const values( bits.begin(), bits.end() );
python( &values[0], safe_cast<int>( values.size() ) );
}
where "safe_cast" is your favorite safe cast from one integral type to
another, presumably aborting or throwing an exception if the value can't
be represented by the destination type.
--
A: Because it messes up the order in which people normally read text.
Q: Why is it such a bad thing?
A: Top-posting.
Q: What is the most annoying thing on usenet and in e-mail?
Bo Peng wrote: I am using std::vector<boo l> (bit_vector) to store my bit sequence. To
access the same sequence from C (to expose to a python module), I need
to know the pointer and offset of vector::<bool>: :iterator (or
reference). However, given a std::vector<boo l> a, all a.begin(), a[0]
etc are instances of a proxy class so I can not do things like
&*a.begin(). Is there a safe way to get the information I need?
No. Bits have no separate address.
V
Victor Bazarov wrote: Bo Peng wrote:
I am using std::vector<boo l> (bit_vector) to store my bit sequence. To
access the same sequence from C (to expose to a python module), I need
to know the pointer and offset of vector::<bool>: :iterator (or
reference). However, given a std::vector<boo l> a, all a.begin(), a[0]
etc are instances of a proxy class so I can not do things like
&*a.begin(). Is there a safe way to get the information I need?
No. Bits have no separate address.
Really? What I need is actually the starting point of the bits. I.e.,
&*vec.begin( ) if the vector is not vector<bool>. It should not be too
diffcult since bit_vector always starts from the beginning of a WORD.
Cheers,
Bo
Bo Peng wrote: Victor Bazarov wrote:
Bo Peng wrote:
I am using std::vector<boo l> (bit_vector) to store my bit sequence.
To access the same sequence from C (to expose to a python module), I
need to know the pointer and offset of vector::<bool>: :iterator (or
reference). However, given a std::vector<boo l> a, all a.begin(), a[0]
etc are instances of a proxy class so I can not do things like
&*a.begin(). Is there a safe way to get the information I need?
No. Bits have no separate address.
Really? What I need is actually the starting point of the bits. I.e.,
&*vec.begin( ) if the vector is not vector<bool>. It should not be too
diffcult since bit_vector always starts from the beginning of a WORD.
There is no requirement that 'vector<bool>' keeps its bits in the same
array, same value, or same {whatever_other _collection_you _can_think_of}.
So, if you _know_ that those bits are a contiguous representation of some
kind of integral value (or whatever you think they are), you know already
where and/or how to get them.
All I can suggest is to repackage them as you need them, just like Alf
explained.
V
Victor Bazarov wrote: All I can suggest is to repackage them as you need them, just like Alf
explained.
The problem is that the goal of this python module is to *expose* the
underlying vector<bool> (other vectors are easy and have been done) and
allow users to read/write the vector directly. For example
v = getVector(); # return a python object v
print v
print v[2]
v[0] = 1
v[3] = 0
Bo
> For that you need to provide a wrapper to the python side.
Exactly. I have already working code for other vectors. The python
wrapper object knows vector type and starting pointer and can correctly
read/write vector items. In the case of vector<bool>, I am unable to get
the starting address.
The only way out may be extending python in C++, instead of C. I mean,
store a vector reference directly instead of pointer. I really do not
know how to do this since all examples of extending Python is written in C.
Cheers,
Bo
* Bo Peng: Victor Bazarov wrote:
All I can suggest is to repackage them as you need them, just like Alf
explained.
The problem is that the goal of this python module is to *expose* the
underlying vector<bool> (other vectors are easy and have been done) and
allow users to read/write the vector directly. For example
v = getVector(); # return a python object v
print v
print v[2]
v[0] = 1
v[3] = 0
For that you need to provide a wrapper to the python side.
--
A: Because it messes up the order in which people normally read text.
Q: Why is it such a bad thing?
A: Top-posting.
Q: What is the most annoying thing on usenet and in e-mail?
On Tue, 31 Jan 2006 18:54:00 -0600, Bo Peng <bp***@rice.edu > wrote:
For that you need to provide a wrapper to the python side.
Exactly. I have already working code for other vectors. The python
wrapper object knows vector type and starting pointer and can correctly
read/write vector items. In the case of vector<bool>, I am unable to get
the starting address.
vector<bool> is an exception to all other vectors. You cannot access
its storage directly like a buffer, neither in C++ nor in any other
language. As the C++ standard says, the reference returned by
vector<bool>::o perator[] is some kind of proxy class that lets you
read and write individual bool elements, but that's all.
If you can't do it in C++, "extending Python" won't help, either.
The only way out may be extending python in C++, instead of C. I mean,
store a vector reference directly instead of pointer. I really do not
know how to do this since all examples of extending Python is written in C.
Cheers,
Bo
--
Bob Hairgrove No**********@Ho me.com This thread has been closed and replies have been disabled. Please start a new discussion. Similar topics | |
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