调整结构中的向量的大小

Question

I have defined two struct s

class foo() {
public:
    struct spatialEntry {
        bool block;
        CoherenceState_t state;
    };

    struct accumulationEntry {
        uint64_t offset;
        std::vector<spatialEntry> pattern;
    };

    std::vector<int> v;
    std::list<accumulationEntry> accumulationTable;

    foo() {
        v.resize(16);
    }
};

Now I want to initialize the size of std::vector<spatialEntry> to 16 like v . How can I do that?

Answer 1

Just define a constructor for the class which contains that member and then resize() as:

class foo() {
public:
   //...
   struct accumulationEntry 
   {
       uint64_t offset;
       std::vector<spatialEntry> pattern;
       accumulationEntry()
       {
            pattern.resize(16);  //<--------- this is what you want?
       }
    };
    std::vector<int> v;
    std::list< accumulationEntry > accumulationTable;
    foo()
    {
       v.resize(16);
    }
};

But then if you use resize , then it is better to do that as :

       accumulationEntry() : pattern(16)  //<--- note this
       {
            //pattern.resize(16);
       }

That is, use member-initialization list. Do the same for foo also.

Answer 2

accumulationEntry is just a type. You don't yet have an object of that type, so there is no std::vector<spatialEntry> to resize. Presumably you will be adding accumulationEntry s to your accumulationTable . You might do that like this:

accumulationTable.push_back(accumulationEntry());

Once you have done that, you can resize the vector contained in, for example, the 0th element like so:

accumulationTable[0].pattern.resize(16);

Alternatively, you could provide a constructor for accumulationEntry that resizes its pattern member:

struct accumulationEntry {
  // ...
  accumulationEntry()
  {
    pattern.resize(16);
  }
};

Answer 3

class foo() {
public:
 struct spatialEntry {
   bool block;
   CoherenceState_t state;
 };
 struct accumulationEntry {
 accumulationEntry()
     : pattern(16)  //  Calling pattern's c'tor
 {
 }
   uint64_t offset;
   std::vector<spatialEntry> pattern;
 };
 std::vector<int> v;
 std::list< accumulationEntry > accumulationTable;
 foo()
 {
    v.resize(16);
 }
};