矢量push_back不在类对象中工作

时间:2012-06-28 14:23:12

标签: c++ vector push-back

我正在制作各种各样的层次结构,并且无法在向量中添加元素。我简化了代码,仍然无法按预期向向量添加元素。层次结构如下:

Pdb>链>字符串

Pdb和Chain是类名,字符串是属于Chain的向量的名称。我不能push_back为字符串添加字符串。您可以更好地查看我的代码:

连锁课:

class Chain {
  string chain_id;
  vector<string> strings;

public:
  Chain(string id_) { chain_id = id_; }
  vector<string> GetStrings() { return strings; }
  void AddString(string s) { 
    cout << "Size of strings BEFORE push_back in AddString: " << strings.size() << endl;
    strings.push_back(s); 
    cout << "Size of strings AFTER push_back in AddString: " << strings.size() << endl;
  }
  string GetChainId() { return chain_id; }
};

Pdb类:

class Pdb {
  string pdb_id;
  vector<Chain> chains;

public:
  Pdb(string id_) { pdb_id = id_; }
  vector<Chain> GetChains() { return chains; }
  void AddChain(Chain c) { chains.push_back(c); }
  string GetPdbId() { return pdb_id; }
};

主:

int main () {

  vector<Pdb> pdbs;
  pdbs.push_back(Pdb("1ubq"));
  cout << "\n\t1. " << pdbs[0].GetPdbId() << endl;
  pdbs[0].AddChain(Chain("A"));
  cout << "\n\t2. " << pdbs[0].GetChains()[0].GetChainId() << endl;
  pdbs[0].GetChains()[0].AddString("Whateva");
  cout << "\n\t3. Size of strings after AddString in main: " << pdbs[0].GetChains()[0].GetStrings().size() << endl;
  return 0;
}

输出:

1. 1ubq

2. A
Size of strings BEFORE push_back in AddString: 0
Size of strings AFTER push_back in AddString: 1

3. Size of strings after AddString in main: 0

正如您所看到的,AddString函数正在向AddString函数本身添加一个元素,但是当我将GetStrings返回main时,执行AddString后,字符串为空。我不明白为什么会这样。任何帮助将不胜感激。

1 个答案:

答案 0 :(得分:4)

问题是您返回该成员的副本,而不是成员本身:

vector<Chain> GetChains()

应该是

vector<Chain>& GetChains()

为此工作。

我必须指出,你严重违反了单一责任原则。你直接对会员进行操作,这不是一个好主意。考虑更换:

pdbs[0].GetChains()[0].AddString("Whateva");

类似

pdbs[0].AddStringToChain(0,"Whateva");