初始化 vector<doubles> c++ 的向量
声明：本页面是StackOverFlow热门问题的中英对照翻译，遵循CC BY-SA 4.0协议，如果您需要使用它，必须同样遵循CC BY-SA许可，注明原文地址和作者信息，同时你必须将它归于原作者（不是我）：StackOverFlow
原文地址: http://stackoverflow.com/questions/7519215/
Warning: these are provided under cc-by-sa 4.0 license. You are free to use/share it, But you must attribute it to the original authors (not me):
StackOverFlow
initializing a vector of vector<doubles> c++
提问by smilingbuddha
Hi I want to initialize a size 9 vector whose elements are vectors of the size, say 5. I want to initialize all the elements to the zero vector.
嗨，我想初始化一个大小为 9 的向量，其元素是大小的向量，比如 5。我想将所有元素初始化为零向量。
Is this way correct?
这种方式正确吗？
vector<double> z(5,0);
vector< vector<double> > diff(9, z);
OR is there a shorter way to do this?
或者有没有更短的方法来做到这一点？
回答by bdonlan
You could potentially do this in a single line:
您可以在一行中完成此操作：
vector<vector<double> > diff(9, vector<double>(5));
You might also want to consider using boost::multi_arrayfor more efficient storage and access (it avoids double pointer indirection).
您可能还想考虑使用boost::multi_array来提高存储和访问效率（它避免了双指针间接访问）。
回答by Kerrek SB
You can put it all in one line:
您可以将所有内容放在一行中：
vector<vector<double>> diff(9, vector<double>(5));
This avoids the unused local variable.
这避免了未使用的局部变量。
(In pre-C++11 compilers you need to leave a space, > >.)
（在 C++11 之前的编译器中，您需要留一个空格，> >.）
回答by Mark B
vector< vector<double> > diff(9, std::vector<double>(5, 0));
vector< vector<double> > diff(9, std::vector<double>(5, 0));
However in the specific case where the sizes are known at compile time you coulduse a C array:
但是，在编译时已知大小的特定情况下，您可以使用 C 数组：
double diff[9][5] = { { 0 } };
double diff[9][5] = { { 0 } };
回答by R. Martinho Fernandes
If the sizes are fixed, you can go with std::arrayinstead:
如果尺寸是固定的，您可以std::array改为：
std::array<std::array<double,5>,9> diff = {};
回答by riwalk
Pretty sure this will work:
很确定这会起作用：
vector< vector<double> > diff(9, vector<double>(5,0));
