2 straight forward Questions

[Michael]

Righty,
1: Is there a standard library that contain matrices and complex numbers. I
need to find eigen values of a 3x3 matrix.

2: Is there a way of getting the pointer to the start of an array from the
data stored in a std vector. I load loads of floats into a vector at the
moment to store vertex infomration for openGL, but to render them, I need to
pass a pointer to the beginning of the array to OpenGL, not a vector. At the
moment I'm just compying them into another array, but this seems like a bit
of a waste:

vector<float> vertices;

//Copy data into 'vertices'

Then before rendering I have to :
float* pVertexArray = new float[vertices.size()];
for(int i=0;i< vertices.size() ;i++) pVertexArray[i] = vertices[i];
But this seems silly!

Thanks Mike.

[John Harrison]

"Michael" <sl***********@ hotmail.com> wrote in message
news:c7******** **@hercules.bti nternet.com...

Righty,
1: Is there a standard library that contain matrices and complex numbers. I need to find eigen values of a 3x3 matrix.
There are complex numbers in the header file <complex>

std::complex<do uble> c(1.0, 2.0);
std::complex<do uble> d = c*c;

etc.

There are no matrices as such. But you have a lot of options. You could
write a simple class that does all you need (I think that would be best). Or
you could use a vector of vectors. Of you could use valarray.

2: Is there a way of getting the pointer to the start of an array from the data stored in a std vector.
Yes.
I load loads of floats into a vector at the
moment to store vertex infomration for openGL, but to render them, I need to pass a pointer to the beginning of the array to OpenGL, not a vector. At the moment I'm just compying them into another array, but this seems like a bit of a waste:

vector<float> vertices;

//Copy data into 'vertices'

Then before rendering I have to :
float* pVertexArray = new float[vertices.size()];
for(int i=0;i< vertices.size() ;i++) pVertexArray[i] = vertices[i];
But this seems silly!

Right, just do this

some_function(& vectices[0]);

john

[Jeff Schwab]

Michael wrote:

Righty,
1: Is there a standard library that contain matrices
No, but there are plenty of third-party libraries available, many of
them open source. Try Google.
and complex numbers.
#include <complex>
I need to find eigen values of a 3x3 matrix.

2: Is there a way of getting the pointer to the start of an array from the
data stored in a std vector.

&v[0]; // Not sure the standard mandates this, but I think there's a DR.

[Sharad Kala]

"Michael" <sl***********@ hotmail.com> wrote in message
news:c7******** **@hercules.bti nternet.com...

Righty,
1: Is there a standard library that contain matrices and complex numbers. I
need to find eigen values of a 3x3 matrix.
There is std::complex class (#include <complex>)
No class as such for matrices but you could take a look at valarray.
2: Is there a way of getting the pointer to the start of an array from the
data stored in a std vector. I load loads of floats into a vector at the
moment to store vertex infomration for openGL, but to render them, I need to
pass a pointer to the beginning of the array to OpenGL, not a vector. At the
moment I'm just compying them into another array, but this seems like a bit
of a waste:

vector<float> vertices;

//Copy data into 'vertices'

Then before rendering I have to :
float* pVertexArray = new float[vertices.size()];
for(int i=0;i< vertices.size() ;i++) pVertexArray[i] = vertices[i];

&vec[0] will give you the pointer to the first element.

-Sharad

[Jeff Schwab]

Jeff Schwab wrote:

Michael wrote:

Is there a way of getting the pointer to the start of an array
from the data stored in a std vector.

&v[0]; // Not sure the standard mandates this, but I think there's a DR.

OK, it's (23.2.4.1) in the 2003 normative document.

[Michael]

Guys does this not violate the idea of encapsulation, you are making
assumptions about the implmentation that the data is stored contiguosly and
tightly packed?? Or is it just OK cos thats what the vector class is defined
as?
Mike
"Sharad Kala" <no************ *****@yahoo.com > wrote in message
news:c7******** ****@ID-221354.news.uni-berlin.de...

"Michael" <sl***********@ hotmail.com> wrote in message
news:c7******** **@hercules.bti nternet.com...

Righty,
1: Is there a standard library that contain matrices and complex numbers. I need to find eigen values of a 3x3 matrix.

There is std::complex class (#include <complex>)
No class as such for matrices but you could take a look at valarray.

2: Is there a way of getting the pointer to the start of an array from the data stored in a std vector. I load loads of floats into a vector at the
moment to store vertex infomration for openGL, but to render them, I need to pass a pointer to the beginning of the array to OpenGL, not a vector. At the moment I'm just compying them into another array, but this seems like a bit of a waste:

vector<float> vertices;

//Copy data into 'vertices'

Then before rendering I have to :
float* pVertexArray = new float[vertices.size()];
for(int i=0;i< vertices.size() ;i++) pVertexArray[i] = vertices[i];

&vec[0] will give you the pointer to the first element.

-Sharad

[John Harrison]

"Michael" <sl***********@ hotmail.com> wrote in message
news:c7******** **@hercules.bti nternet.com...

Guys does this not violate the idea of encapsulation, you are making
assumptions about the implmentation that the data is stored contiguosly and tightly packed?? Or is it just OK cos thats what the vector class is defined as?

The standard guarantees that the data is stored contiguously.

john

[Siemel Naran]

"John Harrison" <jo************ *@hotmail.com> wrote in message
news:c759t5$ilk h5$1@ID-

"Michael" <sl***********@ hotmail.com> wrote in message

I need to
pass a pointer to the beginning of the array to OpenGL, not a vector

some_function(& vectices[0]);

This will fail for a vector of zero elements. If you know for certain
you'll have data, fine. Otherwise try

some_function(v ectices.size() ? &vectices[0] : NULL);

[Jeff Schwab]

Siemel Naran wrote:

"John Harrison" <jo************ *@hotmail.com> wrote in message
news:c759t5$ilk h5$1@ID-

"Michael" <sl***********@ hotmail.com> wrote in message

I need to
pass a pointer to the beginning of the array to OpenGL, not a vector

some_function (&vectices[0]);

This will fail for a vector of zero elements. If you know for certain
you'll have data, fine. Otherwise try

some_function(v ectices.size() ? &vectices[0] : NULL);

Right-o. Another special case (other than an empty vector) is a
specialization like std::vector<boo l>. I'm not sure what happens in
that case.

[Sharad Kala]

"Michael" <sl***********@ hotmail.com> wrote in message
news:c7******** **@hercules.bti nternet.com...

Guys does this not violate the idea of encapsulation, you are making
assumptions about the implmentation that the data is stored contiguosly and
tightly packed?? Or is it just OK cos thats what the vector class is defined
as?

The 2003 "technical corrigendum" 23.2.4[1] says "The elements of a vector are
stored contiguously".