Ale Ale - 1 year ago 163
C++ Question

Vector: initialization or reserve?

I know the size of a vector, which is the best procedure to initialize it?:

option 1

vector<int> vec(3); //in .h; //in .cpp; //in .cpp; //in .cpp


vector<int> vec; //in .h
vec.reserve(3); //in .cpp
vec.push_back(var1); //in .cpp
vec.push_back(var2); //in .cpp
vec.push_back(var3); //in .cpp

I guess the option 2 is better than 1. is it? other options?

Answer Source

Both variants have different semantics, i.e. you are comparing apples and oranges.

The first gives you a vector of n default-initialized values, the second variant reserves the memory, but does not initialize them.

Choose what better fits your needs, i.e. what is "better" in a certain situation.

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