Passing array by reference

[john]

Guys,

quick question - got a function like:

void CalculateApproach(float (&Params)[4], double (&ObjectPos)[3],
double (&VehiclePos)[4], double (&NewPos)[4])


OK, the seconds argument should come from an array but this array is
bigger than the expected 3 i.e it has 10 elements but I only need 4,5
and 6 so I tried something like:

CalculateApproach(fAppParams, &dFeatures[4], dCurVehPos, dNewVehPos);

but it fails for me. Am I trying to do something that is not allowed and
hence should just make new array[3] and copy my values in and then pass
it into the function or can someone give me hint towards the syntax i
should be using if it can work?



Cheers,


John.

 

[Victor Bazarov]

Guys,

quick question - got a function like:

void CalculateApproach(float (&Params)[4], double (&ObjectPos)[3],
double (&VehiclePos)[4], double (&NewPos)[4])


OK, the seconds argument should come from an array but this array is
bigger than the expected 3 i.e it has 10 elements but I only need 4,5
and 6 so I tried something like:

CalculateApproach(fAppParams, &dFeatures[4], dCurVehPos, dNewVehPos);

but it fails for me. Am I trying to do something that is not allowed

Yes, essentially.

and hence should just make new array[3] and copy my values in and
then pass it into the function or can someone give me hint towards
the syntax i should be using if it can work?

You could try forcing it with a cast...

void foo(int (&ar)[3])
{
ar[0] = 1;
ar[1] = 11;
ar[2] = 111;
}
#include <cassert>
int main()
{
typedef int (*pArrayOf3int)[3];
int array[10] = {};
foo(*pArrayOf3int(array + 5));
assert(array[5] == 1);
assert(array[6] == 11);
assert(array[7] == 111);
}

V

 

[Carl Barron]

Guys,

quick question - got a function like:

void CalculateApproach(float (&Params)[4], double (&ObjectPos)[3],
double (&VehiclePos)[4], double (&NewPos)[4])


OK, the seconds argument should come from an array but this array is
bigger than the expected 3 i.e it has 10 elements but I only need 4,5
and 6 so I tried something like:

CalculateApproach(fAppParams, &dFeatures[4], dCurVehPos, dNewVehPos);

but it fails for me. Am I trying to do something that is not allowed and
hence should just make new array[3] and copy my values in and then pass
it into the function or can someone give me hint towards the syntax i
should be using if it can work?

typedef double DoubleFour[4];
typedef double DoubleThree[3];

void CalculateApproach(DoubleFour &,DoubleThree &,DoubleFour
&,DoubleFor &);

CalculateApproach(fAppParams, (DoubleThree &)(dFeatures[4]),
dCurVehPOs,dNewVehPos);

this should work, as an array must be decayable to a pointer so the
cast is only to tell the compiler what is going on. A reinterpret_cast
will be needed and this is a strong warning that it might not be
portable.

 

[Jim Langston]

Guys,

quick question - got a function like:

void CalculateApproach(float (&Params)[4], double (&ObjectPos)[3], double
(&VehiclePos)[4], double (&NewPos)[4])


OK, the seconds argument should come from an array but this array is
bigger than the expected 3 i.e it has 10 elements but I only need 4,5 and
6 so I tried something like:

CalculateApproach(fAppParams, &dFeatures[4], dCurVehPos, dNewVehPos);

Calculateapproache( float&* fAppParams, double& dFeatures[4], double&*
dcurVehPos, double&* dNewVehPos )

but it fails for me. Am I trying to do something that is not allowed and
hence should just make new array[3] and copy my values in and then pass it
into the function or can someone give me hint towards the syntax i should
be using if it can work?



Cheers,


John.

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[Victor Bazarov]

Guys,

quick question - got a function like:

void CalculateApproach(float (&Params)[4], double (&ObjectPos)[3],
double (&VehiclePos)[4], double (&NewPos)[4])


OK, the seconds argument should come from an array but this array is
bigger than the expected 3 i.e it has 10 elements but I only need
4,5 and 6 so I tried something like:

CalculateApproach(fAppParams, &dFeatures[4], dCurVehPos, dNewVehPos);

Calculateapproache( float&* fAppParams, double& dFeatures[4], double&*
dcurVehPos, double&* dNewVehPos )

The OP's line looks like a function call, and yours looks like
a declaration. Are you sure that's what he's asking about?

[..]

V

 

[john]

Guys,

quick question - got a function like:

void CalculateApproach(float (&Params)[4], double (&ObjectPos)[3],
double (&VehiclePos)[4], double (&NewPos)[4])


OK, the seconds argument should come from an array but this array is
bigger than the expected 3 i.e it has 10 elements but I only need 4,5
and 6 so I tried something like:

CalculateApproach(fAppParams, &dFeatures[4], dCurVehPos, dNewVehPos);

but it fails for me. Am I trying to do something that is not allowed and
hence should just make new array[3] and copy my values in and then pass
it into the function or can someone give me hint towards the syntax i
should be using if it can work?



Cheers,


John.

Thanks guys, the cast worked. I thought I could use a cast but was
unsure about the syntax but using the typedef sorted it!

Thanks again.


John.

 

[Jim Langston]

Guys,

quick question - got a function like:

void CalculateApproach(float (&Params)[4], double (&ObjectPos)[3],
double (&VehiclePos)[4], double (&NewPos)[4])


OK, the seconds argument should come from an array but this array is
bigger than the expected 3 i.e it has 10 elements but I only need
4,5 and 6 so I tried something like:

CalculateApproach(fAppParams, &dFeatures[4], dCurVehPos, dNewVehPos);

Calculateapproache( float&* fAppParams, double& dFeatures[4], double&*
dcurVehPos, double&* dNewVehPos )

The OP's line looks like a function call, and yours looks like
a declaration. Are you sure that's what he's asking about?

Actually, no. And re-reading I think I answered a question he didn't ask.

 

[Mathias Gaunard]

void CalculateApproach(float (&Params)[4], double (&ObjectPos)[3],
double (&VehiclePos)[4], double (&NewPos)[4])

OK, the seconds argument should come from an array but this array is
bigger than the expected 3 i.e it has 10 elements but I only need 4,5
and 6 so I tried something like:

CalculateApproach(fAppParams, &dFeatures[4], dCurVehPos, dNewVehPos);

but it fails for me. Am I trying to do something that is not allowed

Yes.
The type of &dFeatures[4] is double*, with certainly isn't an array of
three doubles or a reference to one, but only a pointer to a double.

and
hence should just make new array[3] and copy my values in and then pass
it into the function

That's a possible solution.

or can someone give me hint towards the syntax i
should be using if it can work?

You could use some reinterpret_casts, but that's evil too.
The correct way would probably be to design your function differently.