Clash Royale CLAN TAG#URR8PPP

set static variable in function only once

So I was wondering if it is possible to set a static variable inside a function scope only once. For example consider this function:

void projectPointIntoPlane(const Affine3f& plane2xy, Vector3f& p)

static Matrix3f P;
P << Vector3f::UnitX(), Vector3f::UnitY(), Vector3f::Zero();

p = plane2xy.inverse() * P * plane2xy * p;



I would like to set P only once and not at every function call, how can I achive this?

3 Answers
3

Instead of declaring P and thereafter initializing it separately, you can initialize it in the declaration, using the finished() method of CommaInitializer:

P

finished()

CommaInitializer

static const Matrix3f P =
(Matrix3f() << Vector3f::UnitX(), Vector3f::UnitY(),
Vector3f::Zero()).finished();


With this approach, you can also declare P as const.

P

const

finished()

You could use a lambda that returns the right value. Since it's in the initialization expression, it's only called once:

void projectPointIntoPlane(const Affine3f& plane2xy, Vector3f& p)

static Matrix3f P =
Matrix3f P;
P << Vector3f::UnitX(), Vector3f::UnitY(), Vector3f::Zero();
return P;
();

p = plane2xy.inverse() * P * plane2xy * p;



Something along these lines:

static Matrix3f P;
static bool dummy = (
(P << Vector3f::UnitX(), Vector3f::UnitY(), Vector3f::Zero()),
true);


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