在我们的c++课程中,他们建议不要再在新项目中使用c++数组。据我所知,Stroustroup本人建议不要使用数组。但是否存在显著的性能差异?
当前回答
两者之间的性能差异很大程度上取决于实现——如果你比较一个实现得很差的std::vector和一个优化的数组实现,数组会赢,但是反过来,vector会赢……
As long as you compare apples with apples (either both the array and the vector have a fixed number of elements, or both get resized dynamically) I would think that the performance difference is negligible as long as you follow got STL coding practise. Don't forget that using standard C++ containers also allows you to make use of the pre-rolled algorithms that are part of the standard C++ library and most of them are likely to be better performing than the average implementation of the same algorithm you build yourself.
也就是说,以我之见,vector在使用调试STL的调试场景中胜出,因为大多数具有适当调试模式的STL实现至少可以突出/清除人们在使用标准容器时所犯的典型错误。
哦,不要忘记数组和vector共享相同的内存布局,因此您可以使用vector将数据传递给需要基本数组的遗留C或c++代码。但是,请记住,在这种情况下,大多数赌注都是无效的,您将再次处理原始内存。
其他回答
有时候数组确实比向量好。如果你总是在操纵别人 固定长度的对象集合,数组更好。考虑下面的代码片段:
int main() {
int v[3];
v[0]=1; v[1]=2;v[2]=3;
int sum;
int starttime=time(NULL);
cout << starttime << endl;
for (int i=0;i<50000;i++)
for (int j=0;j<10000;j++) {
X x(v);
sum+=x.first();
}
int endtime=time(NULL);
cout << endtime << endl;
cout << endtime - starttime << endl;
}
X的向量在哪里
class X {
vector<int> vec;
public:
X(const vector<int>& v) {vec = v;}
int first() { return vec[0];}
};
X的数组版本为:
class X {
int f[3];
public:
X(int a[]) {f[0]=a[0]; f[1]=a[1];f[2]=a[2];}
int first() { return f[0];}
};
数组版本的main()将更快,因为我们避免了 每次在内部循环中“new”的开销。
(此代码由我发布到comp.lang.c++)。
两者之间的性能差异很大程度上取决于实现——如果你比较一个实现得很差的std::vector和一个优化的数组实现,数组会赢,但是反过来,vector会赢……
As long as you compare apples with apples (either both the array and the vector have a fixed number of elements, or both get resized dynamically) I would think that the performance difference is negligible as long as you follow got STL coding practise. Don't forget that using standard C++ containers also allows you to make use of the pre-rolled algorithms that are part of the standard C++ library and most of them are likely to be better performing than the average implementation of the same algorithm you build yourself.
也就是说,以我之见,vector在使用调试STL的调试场景中胜出,因为大多数具有适当调试模式的STL实现至少可以突出/清除人们在使用标准容器时所犯的典型错误。
哦,不要忘记数组和vector共享相同的内存布局,因此您可以使用vector将数据传递给需要基本数组的遗留C或c++代码。但是,请记住,在这种情况下,大多数赌注都是无效的,您将再次处理原始内存。
如果使用向量表示多维行为,则会对性能造成影响。
2d+向量会导致性能下降吗?
其要点是,每个子向量都有大小信息,因此会有少量开销,并且不一定会有数据序列化(与多维c数组不同)。这种串行化的缺乏可以提供比微优化更大的机会。如果你在做多维数组,最好扩展std::vector并滚动你自己的get/set/resize bits函数。
向量使用的内存比数组多一点,因为它们包含数组的大小。它们还会增加程序的硬盘大小,可能还会增加程序的内存占用。这些增加很小,但如果您使用的是嵌入式系统,则可能很重要。尽管这些差异很重要的大多数地方都是使用C而不是c++的地方。
STL is a heavily optimized library. In fact, it's even suggested to use STL in games where high performance might be needed. Arrays are too error prone to be used in day to day tasks. Today's compilers are also very smart and can really produce excellent code with STL. If you know what you are doing, STL can usually provide the necessary performance. For example by initializing vectors to required size (if you know from start), you can basically achieve the array performance. However, there might be cases where you still need arrays. When interfacing with low level code (i.e. assembly) or old libraries that require arrays, you might not be able to use vectors.