[英]How to use Struct with a *variable name?
private:
// data containing character strings
// shared by Strings when copying/assigning
struct SharedData
{
char *data; // 0-terminated char array
size_t n; // number of non-0 characters in string
size_t count; // reference count, how many Strings share this object?
};
SharedData *shared; //here i don't understand how to use.
How do I use n? 如何使用n?
do I just do this 我只是这样做吗
shared -> n = 3;
I keep getting segmentation faults so i don't know what i am doing. 我不断出现细分错误,所以我不知道自己在做什么。 I want to grab the length of a string and then pass it to n to be stored
我想获取一个字符串的长度,然后将其传递给n进行存储
Your class contains a pointer to SharedData. 您的类包含一个指向 SharedData的指针 。 You need to make that pointer point to something, presumably by doing this
您需要使指针指向某物,大概是通过这样做
shared = new SharedData();
shared->n = 3;
// etc.
Same thing is true of data inside shared 共享内部的数据也是如此
shared->data = new char[100];
strcpy(shared->data, ...);
I have a feeling this is going to be quite a hard exercise for you if you don't have a good grasp of pointers yet. 如果您还没有很好地掌握指针,我感觉这对您来说将是一项艰巨的练习。
You should allocate some memory first: 您应该先分配一些内存:
SharedData *shared = new SharedData;
shared->n = 3;
Better use something like this: 最好使用这样的东西:
struct SharedData {
SharedData(size_t Capacity) : data(0), capacity(Capacity), length(0), count(1) {
data = new char[capacity];
}
~SharedData() {
if (--count <= 0) delete [] data;
}
char *data; // 0-terminated char array
size_t length; // number of non-0 characters in string
size_t capacity;
size_t count; // reference count, how many Strings share this object?
};
SharedData* shared = new SharedData(1000);
Edit: Of course this short example lacks of copy constructor and handle reference counting in appropriate manner. 编辑:当然,这个简短的示例缺少复制构造函数,并且无法以适当的方式处理引用计数。 But this is not subject of this answer.
但这不是此答案的主题。
Modifying an un-allocated point in memory is undefined behavior. 修改内存中的未分配点是未定义的行为。
You must allocate memory for shared
or set it to a valid address. 您必须为
shared
分配内存或将其设置为有效地址。
class Class
{
private:
SharedData *shared;
...
public:
Class() : shared(new SharedData()) {}
~Class() { delete shared; }
void doSomething() { shared->n = 3; }
};
Try not to use bare pointers when you can use smart pointers: 当可以使用智能指针时,请尽量不要使用裸指针:
class Class
{
private:
std::unique_ptr<SharedData> shared;
or
std::shared_ptr<SharedData> shared;
...
public:
Class() : shared(new SharedData()) {}
void doSomething() { shared->n = 3; }
};
Are you using a C++11 compiler? 您正在使用C ++ 11编译器吗? Why don't you make it a bit easier?
您为什么不轻松一点?
struct SharedData
{
std::string data;
size_t count; // reference count, how many Strings share this object?
};
std::shared_ptr<SharedData> shared = std::make_shared<SharedData>();
If you don't need the actual count of the number of referrers, you just want to know if there is anyone referencing your data, simply use a std::shared_ptr<std::string>
. 如果您不需要实际的引荐来源人数计数,您只想知道是否有人在引用您的数据,只需使用
std::shared_ptr<std::string>
。 It will keep track of references and destroy the string object when all the references are gone. 当所有引用消失时,它将跟踪引用并销毁字符串对象。
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