CODEWITHSUNDEEP
c++structmemcpy
tmighty
tmighty

Reputation: 11399

C++ Using memcpy to fill a vector in a struct

I would like to fill a struct using memcpy.

The struct is declared like this:

struct udtFeatures
{
    vector<unsigned char>ByteFeatures;
};

And this is where I would like fill the bytes:

void clsMapping::FeedFeaturesFromMap(udtFeatures &uFeatures,int uOtherIndex)
{
    int iBytePos=this->Content()[uOtherIndex].ByteStart;
    int iByteCount=this->Content()[uOtherIndex].ByteCount;

    memcpy(uFeatures.ByteFeatures, &((char*)(m_pVoiceData))[iBytePos],iByteCount);
}

However memcpy does not like this.

The compiler says:

No matching conversion function found for 

std::vector<unsigned char, std::allocator<unsigned char>> in void *.

I guess it is because it .ByteFeatures is just a pointer?

How could I do this?

Upvotes: 1

Views: 3318

Answers (4)

fatihk
fatihk

Reputation: 7919

uFeatures.ByteFeatures should be &uFeatures.ByteFeatures[0]

Upvotes: 0

Mike Seymour
Mike Seymour

Reputation: 254581

I guess it is because it .ByteFeatures is just a pointer?

No, it's because it isn't just a pointer. It's a vector.

How could I do this?

If you want a pointer to the array managed by the vector, then that's uFeatures.ByteFeatures.data() or &uFeatures.ByteFeatures[0]. Alternatively, you might consider using std::copy instead.

In either case, make sure the vector is large enough before copying things into it.

Upvotes: 5

Martin Perry
Martin Perry

Reputation: 9527

You cant fill std::vector using memcpy (Well.. there is a way, but for you is better to think it as if not). Use std::copy or fill it by yourself.

Upvotes: 0

Some programmer dude
Some programmer dude

Reputation: 409256

It would be possible to use memcpy to initialize a std::vector, but not advisable.

Instead use std::copy:

std::copy(&m_pVoiceData[iBytePos], &m_pVoiceData[iBytePos + iByteCount],
          std::back_inserter(uFeatures.ByteFeatures));

Upvotes: 0

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