向量:初始化还是保留? [英] Vector: initialization or reserve?
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问题描述
我知道向量的大小,这是初始化向量的最佳方法吗?
I know the size of a vector, which is the best way to initialize it?
选项1:
vector<int> vec(3); //in .h
vec.at(0)=var1; //in .cpp
vec.at(1)=var2; //in .cpp
vec.at(2)=var3; //in .cpp
选项2:
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
我猜想,Option2比Option1更好。是吗?还有其他选择吗?
I guess, Option2 is better than Option1. Is it? Any other options?
推荐答案
两个变体都有不同的语义,即您要比较苹果和橘子。
Both variants have different semantics, i.e. you are comparing apples and oranges.
第一个为您提供n个默认初始化值的向量,第二个变量保留内存,但不初始化它们。
The first gives you a vector of n default-initialized values, the second variant reserves the memory, but does not initialize them.
选择什么会更适合您的需求,即在特定情况下更好的东西。
Choose what better fits your needs, i.e. what is "better" in a certain situation.
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