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PeterVarain
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memcpy vector to array in QT

Hi everybody,

I have a small problem here... I need to copy the contents of a vector to a certain position in an array. However, memcpy returns the error "invalid conversion from int to void*"
Here's an example of what I'm trying to do:

QVector<qint16> Vector1(1024);
QVector<qint16> Vector2(1024);
QVector<qint16> Vector3(1024);

int HArr[1024][1024];

memcpy(HArr[0][0], &Vector1[0], 1024);
memcpy(HArr[0][1], &Vector2[0], 1024);
memcpy(HArr[0][2], &Vector3[0], 1024);

Can someone show me how to do this correctly ?

Thanks,
Peter

C++Linux

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sarabande

8/22/2022 - Mon
ASKER CERTIFIED SOLUTION
jkr

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mccarl

Oh yeah, plus what jkr says about the amount of data to memcpy.
mccarl

jkr, you still need to take the address of the first parameters
PeterVarain

ASKER
I've tried all the suggestions but I still get the same error...

Regards,
Peter
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SOLUTION
sarabande

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jkr

>>"invalid conversion from int to void*"

Aaah, I think everyone missed that little detail - you are not using the target arrays correctly, that should be
QVector<qint16> Vector1(1024);
QVector<qint16> Vector2(1024);
QVector<qint16> Vector3(1024);

short int HArr[1024][1024]; // 'short int' as the equivalent to 'quint16'

memcpy(HArr[0], Vector1.constData(), 1024 * sizeof(quint16));
memcpy(HArr[1], Vector2.constData(), 1024 * sizeof(quint16));
memcpy(HArr[2], Vector3.constData(), 1024 * sizeof(quint16));

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sarabande

thanks.

the last code of jkr also works cause  &HArr[0][0]  and HArr[0] both point to first element of the first row of HArr.

did you notice the

 if (sizeof(quint16) == sizeof(short int))

i added?

the point is that it is dangerous when using memcpy to calculate the size to copy from the elements of the right side when the left side elements have a different type.

a short int not necessarily must have 16 bits but could grow in future. so if a system would use a 64-bit int, it very likely would make short int 32-bit.

Sara
mccarl

I think both jkr and I deserve some of the points (in addition to sarabande) as jkr was the first person to get the correct pointer to copy from (http:#a35061677) and the correct size to copy (http:#a35061699) and I was the first person to get the correct destination pointer to copy to (http:#a35061698). Sara had the idea about checking for the size of the data items (http:#a35068086)
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sarabande

mccarl is right. i didn't see the 'Instead of'  in his solution or i would have refered to.

an equal split would be best.

Sara