在 C++ 中初始化结构数组
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Initialization of an array of structs in C++
提问by JustKash
If I have a struct like below:
如果我有一个像下面这样的结构：
typedef struct MyStruct {
char **str;
int num;
} MyStruct;
Is there a way for me to initialize an array of this structures. Perhaps like below:
有没有办法让我初始化这个结构的数组。也许像下面：
const MyStruct MY_STRUCTS[] = {
{
{"Hello"},
1
},
{
{"my other string"},
3
},
};
Ultimately I would like to have a constantly declared array of structs inside a C++ class. How can this be done? Is it possible to have a privately declared member that is pre-initialized?
最终，我希望在 C++ 类中有一个不断声明的结构数组。如何才能做到这一点？是否可以有一个预先初始化的私有声明成员？
回答by Kerrek SB
Sure, you'd write it like this:
当然，你会这样写：
#include <string>
#include <vector>
struct MYStruct
{
std::vector<std::string> str;
int num;
};
MyStruct const data[] = { { { "Hello", "World" }, 1 }
, { { "my other string" }, 3 }
};
Unless I'm misunderstanding and you actually just want numto count the number of elements. Then you should just have:
除非我误解了你实际上只想num计算元素的数量。那么你应该只需要：
std::vector<std::string> data[] = { { "Hello" }
, { "my", "other", "string" }
};
And you can recover the element sizes with data[0].size(), data[1].size(), etc.
你可以恢复与该元件的尺寸data[0].size()，data[1].size()等等。
If everything is determined statically and you just want a compact reference, you still need to provide storage, but everything is virtually the same as in C:
如果一切都是静态确定的，而您只想要一个紧凑的引用，您仍然需要提供存储空间，但一切都与 C 中的几乎相同：
namespace // internal linkage
{
char const * a0[] = { "Hello" };
char const * a1[] = { "my", "other", "string" };
// ...
}
struct Foo
{
char const ** data;
std::size_t len;
};
Foo foo[] = { { a0, 1 }, { a1, 3 } };
Since the size is std::distance(std::begin(a0), std::end(a0)), you could simplify the last part with a macro that just takes a0as an argument. And instead of handwriting Foo, you might just use std::pair<char const **, std::size_t>.
由于大小为std::distance(std::begin(a0), std::end(a0))，您可以使用仅a0作为参数的宏来简化最后一部分。而不是手写Foo，您可能只使用std::pair<char const **, std::size_t>.
回答by Mats Petersson
You mean something like this:
你的意思是这样的：
// In some headerfile:
// 在一些头文件中：
class X
{
private:
static const MyStruct MY_STRUCTS[];
};
// in some .cpp file:
// 在一些 .cpp 文件中：
const X::MyStruct MY_STRUCTS[] = { { {"Hello"}, 1}, { "Other String"} , 3 } };
That assumes, however, that you have a char *str;, since char **str;requires a secondary variable to take the address off. Or, you could use std::vector<string>, and that would solve the problem.
但是，这假设您有一个char *str;, 因为char **str;需要一个辅助变量来取消地址。或者，您可以使用std::vector<string>, 这样就可以解决问题。
回答by Dietmar Kühl
You can use something like
你可以使用类似的东西
class foo {
MyStruct array[2];
public:
foo()
: array{ { "a", 1 }, { "b", 2 }}
{
}
};
assuming you struct's first member is actually char const*rather than char**as you initialization example suggests.
假设您struct的第一个成员实际上是char const*而不是char**您初始化示例所建议的那样。
