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I've seen some C++ code like this:
std::vector<int> vec;
vec.clear();
vec.push_back(42);
What is the purpose (if any) of clearing the vector right after creating it?
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The vector (like all standard containers) owns the objects inside it. So it is responsible for destroying them. Note: If you vector contains pointers then it owns the pointers (not what the pointers point at). So these need to be deleted.
vector::clear() clear() function is used to remove all the elements of the vector container, thus making it size 0.
The standard mandates that the capacity does not change with a clear as reserve guarantees that further adding of elements do not relocate until the requested capacity is reached. This directly enforces clear to not reduce the capacity.
The C++ function std::vector::clear() destroys the vector by removing all elements from the vector and sets size of vector to zero.
It serves no purpose - the vector is already created in an empty state.
If you are lucky, your compiler will optimize away this redundant call entirely - recent versions of both gcc and clang do exactly that.
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