C ++向量,返回与参数 [英] C++ vector, return vs. parameter
问题描述
可能重复:
如何返回一个对象 in C ++
我想知道以下三种方法是否有区别:
I am wondering if there is a difference between the three following approaches:
void FillVector_1(vector<int>& v) {
v.push_back(1); // lots of push_backs!
}
vector<int> FillVector_2() {
vector<int> v;
v.push_back(1); // lots of push_backs!
return v;
}
vector<int> FillVector_3() {
int tab[SZ] = { 1, 2, 3, /*...*/ };
return vector<int>(tab, tab + SZ);
}
推荐答案
最大的区别是第一种方式追加到现有内容,而另外两个填充空向量。 :)
The biggest difference is that the first way appends to existing contents, whereas the other two fill an empty vector. :)
我认为您要查找的关键字是返回值优化,这应该是相当普遍的(使用G ++,你必须专门关闭它,以防止应用)。也就是说,如果用法如下:
I think the keyword you are looking for is return value optimization, which should be rather common (with G++ you'll have to turn it off specifically to prevent it from being applied). That is, if the usage is like:
vector<int> vec = fill_vector();
那么很可能很容易没有副本(而且函数只是更容易使用)。
then there might quite easily be no copies made (and the function is just easier to use).
如果使用现有的向量
vector<int> vec;
while (something)
{
vec = fill_vector();
//do things
}
然后使用out参数避免创建的向量在一个循环和复制数据。
then using an out parameter would avoid creation of vectors in a loop and copying data around.
这篇关于C ++向量,返回与参数的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持IT屋!