Say I have a std::vector named myVec.
I don't know the exact size it will reach, so i use only myVec.push_back(...).
Can I rely on the fact that after I have pushed_back, size()-1 will give me the index of that last element? Thanks.
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G.Rassovsky
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Yes, *iff* you used `push_back`. – Some programmer dude Jul 24 '14 at 09:53
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That is why for safety use the iterator, instead of using indexes to access elements in a vector. – DumbCoder Jul 24 '14 at 11:25
2 Answers
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You have two separate questions. In the title you ask:
Does std::vector size()-1 ALWAYS give the index of the last element?
No. It does not give the index of the last element if the vector is empty.
Can I rely on the fact that after I have pushed_back, size()-1 will give me the index of that last element?
Yes, if the vector is not empty, then size() - 1 is guaranteed to be the index of the last element.
The Paramagnetic Croissant
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Yes, thanks for pointing that out... I meant only on non-empty vectors and after push_backs, but I can see how the question can be misleading. – G.Rassovsky Jul 24 '14 at 10:00
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For non-empty vectors yes, size()-1 is the index of the last element.
Wojtek Surowka
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@arturn Not sure what is your point. After calling `resize(100)` the vector size is 100, and its last index is 99, which is also `size() - 1`. – Wojtek Surowka Oct 15 '22 at 21:23
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@arturn In C++ null normally means null pointer, or 0 character ending C-style strings. Here we have a vector of int8_t, so talking about nulls may be misleading. The vector after resize will have all elements of the default value zero. – Wojtek Surowka Oct 17 '22 at 12:43