c++ - ADO Recordset Field Value to C++ vector/array(捕获指针值)

Question

我正在尝试通过 Visual C++ (express) 查询 SQL Server (Express) 并将生成的数据集存储到 C++ vector 中(数组也很好)。为此，我研究了 ADO 库并在 MSDN 上找到了大量帮助。简而言之，引用 msado15.dll 库并使用这些功能(尤其是 ADO 记录绑定(bind)，它需要 icrsint.h)。简而言之，我已经能够查询数据库并使用 printf() 显示字段值；但是当我尝试将字段值加载到 vector 中时遇到了麻烦。

我最初尝试通过将所有内容转换为 char* 来加载值(由于多次类型转换错误后绝望)，结果发现最终结果是一个指针 vector ，它们都指向相同的内存地址。接下来(这是下面提供的代码)我试图分配内存位置的值，但最终只得到内存位置第一个字符的 vector 。简而言之，我需要帮助理解如何传递由 Recordset 字段值 (rs.symbol) 指针存储的整个值(在传递给 vector 时)，而不仅仅是第一个字符？在这种情况下，从 SQL 返回的值是字符串。

#include "stdafx.h"
#import "msado15.dll" no_namespace rename("EOF", "EndOfFile")
#include "iostream"
#include <icrsint.h>
#include <vector>
int j;
_COM_SMARTPTR_TYPEDEF(IADORecordBinding, __uuidof(IADORecordBinding));
inline void TESTHR(HRESULT _hr) { if FAILED(_hr) _com_issue_error(_hr); }
class CCustomRs : public CADORecordBinding {
    BEGIN_ADO_BINDING(CCustomRs)
        ADO_VARIABLE_LENGTH_ENTRY2(1, adVarChar, symbol, sizeof(symbol), symbolStatus, false)
        END_ADO_BINDING()
public:
    CHAR symbol[6];
    ULONG symbolStatus;
};
int main() {
    ::CoInitialize(NULL);
    std::vector<char> tickers;
    try {
        char sym;
        _RecordsetPtr pRs("ADODB.Recordset");
        CCustomRs rs;
        IADORecordBindingPtr picRs(pRs);
        pRs->Open(L"SELECT symbol From Test", L"driver={sql server};SERVER=(local);Database=Securities;Trusted_Connection=Yes;", 
            adOpenForwardOnly, adLockReadOnly, adCmdText);
        TESTHR(picRs->BindToRecordset(&rs));
        while (!pRs->EndOfFile) {
            // Process data in the CCustomRs C++ instance variables.
//Try to load field value into a vector
            printf("Name = %s\n",
                (rs.symbolStatus == adFldOK ? rs.symbol: "<Error>"));


//This is likely where my mistake is
sym = *rs.symbol;//only seems to store the first character at the pointer's address


            // Move to the next row of the Recordset.   Fields in the new row will 
            // automatically be placed in the CCustomRs C++ instance variables.
//Try to load field value into a vector
            tickers.push_back (sym); //I can redefine everything as char*, but I end up with an array of a single memory location...
            pRs->MoveNext();
        }
    }
    catch (_com_error &e) {
        printf("Error:\n");
        printf("Code = %08lx\n", e.Error());
        printf("Meaning = %s\n", e.ErrorMessage());
        printf("Source = %s\n", (LPCSTR)e.Source());
        printf("Description = %s\n", (LPCSTR)e.Description());
    }
    ::CoUninitialize();
//This is me running tests to ensure the data passes as expected, which it doesn't
    std::cin.get();
    std::cout << "the vector contains: " << tickers.size() << '\n';
    std::cin.get();
    j = 0;
    while (j < tickers.size()) {
        std::cout << j << ' ' << tickers.size() << ' ' << tickers[j] << '\n';
        j++;
    }
    std::cin.get();
}

感谢您提供的任何指导。

Answer 1

A std::vector<char*>不起作用，因为相同的缓冲区用于所有记录。所以当pRs->MoveNext()被调用时，新的内容被加载到缓冲区中，覆盖之前的内容。

您需要复制内容。

我建议使用 std::vector<std::string> :

std::vector<std::string> tickers;
...

    tickers.push_back(std::string(rs.symbol));