copy part of vector 1 to vector 2

Hi,

I am trying to copy vector to vector as follow:

Code:

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std::vector<unsigned char> vec1;

//insert some values into vec1

std::vector<unsigned char> vec2;


//now i wanto to copy 2 bytes from vec1 starting at index 5., why do i need to know how many bytes from the end of vec1?? can't i just specify how many bytes i want to copy from starting index?

std::copy(vec1.begin()+5, vec1.end()-??, vec2.begin());

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Quote:

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Originally Posted by mce

why do i need to know how many bytes from the end of vec1?

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You don't, but you do need to know that vec1 has the elements that you want to copy.

Quote:

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Originally Posted by mce

can't i just specify how many bytes i want to copy from starting index?

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Yes, e.g.,

Code:

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std::vector<unsigned char> vec1;
// insert some values into vec1
// ...

// copy 2 bytes from vec1 starting at index 5.
std::vector<unsigned char> vec2(vec1.begin() + 5, vec1.begin() + 7);

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Same idea applies for std::copy, except that you will need pass std::back_inserter(vec2) as the third argument, otherwise you will be copying to elements that don't exist.

TQ so much, don know why my mind just got stuck when i was shown the example of copy using begin() and end()..... sighhhhhhhhh