Question

我有一个非常小的选项处理功能，我需要经常输入这个功能。所以我不能分配矢量。我需要能够向向量添加一个元素并保存它，所以当我回到这个函数时它仍然是它们。

vector<sStruct> * loadFile(char *myTextFile)
{
    myStruct 
        sStruct; 
    vector<myStruct> 
        vectorAddress,
        vectorData;
vectorData = &vectorAddress;
    string 
        feild1, feild2, feild3, feild4;

    ifstream 
        *inFile = new ifstream;

    inFile->open( myTextFile, ios::in );


    if ( !inFile->good() )
    {
         cout << "? File Doesnt Exist! " << endl;
    }

    while ( !inFile->eof() )
    {

// reading a file deliimted  by commas hi,hello,hey,1234
//...
         getline( *inFile, feild1, ',' );
         sStruct.m_1 = field1;
         getline( *inFile, feild2, ',' );
         sStruct.m_2 = field2;
         getline( *inFile, field3, ',' );
         sStruct.m_3; = feild3
         getline( *inFile, feild4 );
         sStruct.m_4 = feield4;

// saving each member of the struct in the vector
    vectorAddress.push_back( sStruct );

    }

    inFile->clear();
    inFile->close();

    cout << vectorAddress.size() << endl;
    delete inFile;  
//
   (*vectorData) = vectorAddress;
    return vectorData;
}

// This function tries despretly to add another element saved in struct member varaible
// to the end of the vector. I need the information from the first function to be here. What i think im trying to do is refer to the same address in memory.


vector<sStruct> *  addElement(vector<sStruct> *vAddElement)
{    
    myStruct sAddElement;  // referring to the same struct.
    vector<sStruct> vectorAddress;
    vAddElement = &vectorAddress;

    cout << "Enter a String: ";
    cin  >> sAddElement.feild1  // save user spec in struct member

    vectorAddress.push_back( sAddElement );
    cout << vectorAddress.size() << endl;
    (*vAddElement) = vectorAddress;
    return vAddElement;
}

我试图在不改变功能签名的情况下这样做。

Answer 1

首先，对这类事物使用引用，它减少了不必要的代码，不能为NULL。

在问题上，要添加到矢量，使用push_back或其他一些添加到矢量的方法，你所做的就是尝试分配给矢量：

vector<sStruct> *addElement(vector<sStruct> &vAddElement) {
    myStruct sAddElement;  // referring to the same struct.

    cout << "Enter a String: ";
    cin  >> sAddElement.feild1  // save user spec in struct member

    vAddElement.push_back(sAddElement);
    cout << vectorAddress.size() << endl;

    return &vAddElement; // since you said you must return a pointer (which is silly)
                         // we'll return the address of the object passed in.
}

编辑：为什么你这么多指针（根本没有）你的绝对没有必要用于任何动态分配或获取成员地址的程序。通常的堆栈分配和通过引用传递将允许您使用一半代码（并且正确）执行相同的工作。

编辑：此外，您的循环已损坏，您无法正确测试EOF，直到您尝试读取后。这样做更容易：

while(getline(file, line)) { /* process line */ }

修改

你的这段代码也与你的想法差不多，我会为你推荐，所以你知道：

vector<sStruct> *addElement(vector<sStruct> *vAddElement) { myStruct sAddElement; // ... vector<sStruct> vectorAddress; // creates a new *vector* on the stack vAddElement = &vectorAddress; // makes vAddElement point to the new vector // but does *not* effect the vector whose // address you passed // ... vectorAddress.push_back( sAddElement ); // adds an element to the new vector cout << vectorAddress.size() << endl; // it's size will always be 1, // since you just added the first element (*vAddElement) = vectorAddress; // does absolutely nothing, you are assigning // the new vector to itself return vAddElement; // erroneously returns a pointer to the new vector // it was allocated on the stack and no longer exists // after the return, **never do that ** }

将信息保存在从func到func的向量中

1 个答案: