将std :: wstring转换为SQLWCHAR * [英] Converting std::wstring to SQLWCHAR *

问题描述

我有一个C ++程序，动态创建一个查询字符串，然后传递到使用ODBC连接到数据库的 SQLExecDirect 调用。

I have a C++ program that is dynamically creating a query string which will then be passed to a SQLExecDirect call to connect to a database using ODBC. I'm having trouble passing the variable from one function to another, so I think I must be missing something basic?

在 ConstructQuery

In the ConstructQuery function (which returns type SQLWCHAR *), I have:

std::wstring test = L"test string"; //This test string will actually be several concatenated strings
SQLWCHAR *statement = (SQLWCHAR *)test.c_str();
std::wcout << statement;
return statement;

这样会按预期打印语句变量。但是当我将变量传递给我的主要函数，像这样：

This prints the statement variable as expected. But when I pass the variable to my main function like this:

SQLStatement = ConstructQuery(SQLStatement);
std::wcout << SQLStatement;

我没有输出。

如果不是 statement =（SQLWCHAR *）test.c_str（）;

我使用： statement = Ltest string;

通过罚款，但是我不能在函数的早期部分动态创建测试字符串查询。

The variable passes fine, but then I am not able to dynamically create the "test string" query in the earlier part of the function.

我很难找到很多约 SQLWCHAR 。我猜我可能会转换 std :: wstring 到 SQLWCHAR * 不正确？另一种选择是重写函数，使所有 wstring 都是 SQLWCHAR * ，并以这种方式进行连接 -

I was having a hard time finding out much about SQLWCHAR. I'm guessing that I may be converting std::wstring to SQLWCHAR * incorrectly? Another option would be to rewrite the function so that all of the wstring are SQLWCHAR * and do the concatenation that way - but I'm not sure that's possible and even if it was I don't think it's preferred?

推荐答案

您返回的是一个指向在函数ConstructQuery结束时超出作用域的局部变量的指针。可能最容易通过值返回 std :: wstring ，然后从那里开始工作。

You are returning a pointer to a local variable that goes out of scope at the end of the function ConstructQuery. It might be easiest to return a std::wstring by value and then work from there.

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