C# 中的 StringBuilder 编组问题
我正在尝试使用 C++ dll 来编辑 C# 中的 StringBuilder 对象。我的 C++ 代码如下所示：
extern "C" __declspec(dllexport) void __stdcall PrintHead(char* myString)
{
myString = "testIsOkey";
}
我的 C# 代码为：
[DllImport("StringEdit.dll", CharSet = CharSet.Ansi, SetLastError = true, ExactSpelling = false)]
public static extern void PrintHead([MarshalAs(UnmanagedType.LPStr)] StringBuilder stringBuilder);
private void button1_Click(object sender, EventArgs e)
{
StringBuilder stringBuilder = new StringBuilder("123456");
PrintHead(stringBuilder);
}
调用 PrintHead 后，我期望看到 stringBuilder 对象的值从 "123456" 更改为 "testIsOkey" ，但它没有改变。我不知道我在哪里犯了错误。
感谢您的帮助。
I am trying to use a C++ dll to edit my StringBuilder object in C#. My C++ code looks like this:
extern "C" __declspec(dllexport) void __stdcall PrintHead(char* myString)
{
myString = "testIsOkey";
}
and my C# code is:
[DllImport("StringEdit.dll", CharSet = CharSet.Ansi, SetLastError = true, ExactSpelling = false)]
public static extern void PrintHead([MarshalAs(UnmanagedType.LPStr)] StringBuilder stringBuilder);
private void button1_Click(object sender, EventArgs e)
{
StringBuilder stringBuilder = new StringBuilder("123456");
PrintHead(stringBuilder);
}
After PrintHead is called, i am expecting to see that the stringBuilder object's value is changed from "123456" to "testIsOkey" , but it does not change. I can't figure out where do i make a mistake.
Thanks for your help.
如果你对这篇内容有疑问，欢迎到本站社区发帖提问 参与讨论，获取更多帮助，或者扫码二维码加入 Web 技术交流群。
绑定邮箱获取回复消息
由于您还没有绑定你的真实邮箱，如果其他用户或者作者回复了您的评论，将不能在第一时间通知您！
发布评论
评论（2）
这不是正确的 C++ 代码。它只是更改传递给函数的指针。这没有任何副作用。修复：
但永远不要像这样编写互操作代码，C++ 函数可以通过这种方式轻松破坏垃圾收集堆。这正是您的代码中发生的情况，StringBuilder 的容量不够。您应该添加一个额外的参数来提供传递的缓冲区的大小。修复：
为该额外参数传递字符串构建器的容量，如下所示：
That's not correct C++ code. It merely changes the pointer that was passed to the function. This has no side effects whatsoever. Fix:
But never write interop code like this, the C++ function can easily destroy the garbage collected heap this way. Which is exactly what happens in your code, the StringBuilder's Capacity isn't enough. You should add an extra argument that provides the size of the passed buffer. Fix:
Pass the string builder's Capacity for that extra argument, like this:
是否必须将其标记为
ref或使用其他一些属性，以便 .NET 知道编组应该以两种方式进行？Doesn't it have to be marked
refor with some other attribute, so that .NET knows that the marshalling should occur both ways?