P / Invoke和out参数 [英] P/Invoke and out parameter
问题描述
我遇到的问题很简单。
我在C DLL中有一个函数。我们称之为SomeFunction。这是SomeFunction的原型：
void SomeFunction（char * anArrayOfChars）;
其中anArrayOfChars是一个out参数。
我认为我所要做的就是声明如下：
[DllImport（" someDLL"，CharSet） = CharSet.Auto）]
public static extern void SomeFunction（StringBuilder sBuf）
并在Main函数中调用它：
StringBuilder sBuf = new StringBuilder（128）;
SomeFunction（sBuf）;
我应该有一个由某个函数填充的sBuf。
不幸的是，我得到以下异常：
对象引用未设置为对象的实例。我有什么想法吗？b $ b你做错了吗？
如果你想知道，SomeFunction只是做一个strcpy（anArrayOfChars，
你好，世界！;
提前致谢。
I''m having a problem with something I thought was quite simple.
I have a function in a C DLL. Let''s call it SomeFunction. This is the
prototype for SomeFunction:
void SomeFunction(char * anArrayOfChars);
where anArrayOfChars is an out parameter.
I thought all I had to do was declare it as follows:
[DllImport("someDLL", CharSet = CharSet.Auto)]
public static extern void SomeFunction(StringBuilder sBuf)
and within the Main function call it like that:
StringBuilder sBuf = new StringBuilder(128);
SomeFunction(sBuf);
And I should have an sBuf that was filled by some function.
Unfortunately, I''m getting the following exception:
Object Reference not set to an instance of an object. Any ideas what I''m
doing wrong?
In case you wonder, SomeFunction just does a strcpy(anArrayOfChars,
"Hello, World!);
Thanks in advance.
推荐答案
我认为我所要做的只是声明如下：
[DllImport（" someDLL"，CharSet = CharSet.Auto）]
public static extern void SomeFunction（ StringBuilder sBuf）
I thought all I had to do was declare it as follows:
[DllImport("someDLL", CharSet = CharSet.Auto)]
public static extern void SomeFunction(StringBuilder sBuf)
你应该在这里使用CharSet.Ansi而不是CharSet.Auto。我不知道是否会导致这样的例外。
Mattias
-
Mattias Sj？gren [MVP] mattias @ mvps.org
http://www.msjogren.net/dotnet/ | http://www.dotnetinterop.com
请回复到新闻组。
You should be using CharSet.Ansi rather than CharSet.Auto here. I
don''t know if that would cause such an exception though.
Mattias
--
Mattias Sj?gren [MVP] mattias @ mvps.org
http://www.msjogren.net/dotnet/ | http://www.dotnetinterop.com
Please reply only to the newsgroup.
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"Pollux" <po****@nospam.spam> wrote in message
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我遇到的问题很简单。
我在C DLL中有一个函数。我们称之为SomeFunction。这是SomeFunction的原型：
void SomeFunction（char * anArrayOfChars）;
其中anArrayOfChars是一个out参数。
我认为我所要做的就是声明如下：
[DllImport（" someDLL"，CharSet = CharSet.Auto）]
public static extern void SomeFunction（StringBuilder sBuf）
并在Main函数中调用它：
StringBuilder sBuf = new StringBuilder（128）;
SomeFunction（sBuf）;
我应该有一个由某个函数填充的sBuf。
不幸的是，我得到以下异常：
对象引用未设置为对象的实例。我有什么想法做错了吗？
如果你想知道，SomeFunction只做一个strcpy（anArrayOfChars，
你好，世界！）;
提前致谢。
I''m having a problem with something I thought was quite simple.
I have a function in a C DLL. Let''s call it SomeFunction. This is the
prototype for SomeFunction:
void SomeFunction(char * anArrayOfChars);
where anArrayOfChars is an out parameter.
I thought all I had to do was declare it as follows:
[DllImport("someDLL", CharSet = CharSet.Auto)]
public static extern void SomeFunction(StringBuilder sBuf)
and within the Main function call it like that:
StringBuilder sBuf = new StringBuilder(128);
SomeFunction(sBuf);
And I should have an sBuf that was filled by some function.
Unfortunately, I''m getting the following exception:
Object Reference not set to an instance of an object. Any ideas what I''m
doing wrong?
In case you wonder, SomeFunction just does a strcpy(anArrayOfChars,
"Hello, World!);
Thanks in advance.
SomeFunction的调用显然不会引发异常。你可以吗？
提供一个调用堆栈转储？
因为你返回一个ansi字符串，你需要将你的签名改为：
[DllImport（someDLL）]
public static extern void
SomeFunction（[MarshalAs（UnmanagedType.LPStr）] StringBuilder sBuf）
Willy。
The exception is obviously not thrown by the call of SomeFunction. Could you
provide a call stack dump?
Because you return an ansi string, you need to change your signature into:
[DllImport("someDLL")]
public static extern void
SomeFunction([MarshalAs(UnmanagedType.LPStr)]StringBuilder sBuf)
Willy.
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wi*************@pandora.be says...
Pollux < PO **** @ nospam.spam>在消息中写道
新闻：MP ************************ @ usenet.plus.net ...
"Pollux" <po****@nospam.spam> wrote in message
news:MP************************@usenet.plus.net...
我遇到的问题很简单。
我在C DLL中有一个函数。我们称之为SomeFunction。这是SomeFunction的原型：
void SomeFunction（char * anArrayOfChars）;
其中anArrayOfChars是一个out参数。
我认为我所要做的就是声明如下：
[DllImport（" someDLL"，CharSet = CharSet.Auto）]
public static extern void SomeFunction（StringBuilder sBuf）
并在Main函数中调用它：
StringBuilder sBuf = new StringBuilder（128）;
SomeFunction（sBuf）;
我应该有一个由某个函数填充的sBuf。
不幸的是，我得到以下异常：
对象引用未设置为对象的实例。我有什么想法做错了吗？
如果你想知道，SomeFunction只做一个strcpy（anArrayOfChars，
你好，世界！）;
提前致谢。
I''m having a problem with something I thought was quite simple.
I have a function in a C DLL. Let''s call it SomeFunction. This is the
prototype for SomeFunction:
void SomeFunction(char * anArrayOfChars);
where anArrayOfChars is an out parameter.
I thought all I had to do was declare it as follows:
[DllImport("someDLL", CharSet = CharSet.Auto)]
public static extern void SomeFunction(StringBuilder sBuf)
and within the Main function call it like that:
StringBuilder sBuf = new StringBuilder(128);
SomeFunction(sBuf);
And I should have an sBuf that was filled by some function.
Unfortunately, I''m getting the following exception:
Object Reference not set to an instance of an object. Any ideas what I''m
doing wrong?
In case you wonder, SomeFunction just does a strcpy(anArrayOfChars,
"Hello, World!);
Thanks in advance.
SomeFunction的调用显然不会引发异常。你可以提供一个调用堆栈转储吗？
因为你返回一个ansi字符串，你需要将你的签名改为：
[DllImport（" someDLL"）]
public static extern void
SomeFunction（[MarshalAs（UnmanagedType.LPStr）] StringBuilder sBuf）
Willy。
The exception is obviously not thrown by the call of SomeFunction. Could you
provide a call stack dump?
Because you return an ansi string, you need to change your signature into:
[DllImport("someDLL")]
public static extern void
SomeFunction([MarshalAs(UnmanagedType.LPStr)]StringBuilder sBuf)
Willy.
威利，
对此我很抱歉，我应该提到这一点。调用堆栈建议
从SomeFunction抛出异常。如果我删除了strcpy
的陈述并只是返回或显示一个消息框，我就不会得到
例外。
我猜想不知何故char *并没有指向一个有效的记忆
地址，但我不知道为什么这会因为
而变得难以实现框架应该为我照顾这个吗？
Hi Willy,
Sorry about that, I should have mentioned this. The call stack suggests
that the exception was thrown from SomeFunction. If i remove the strcpy
statment and simply return or display a messagebox, I don''t get an
exception.
I would guess that somehow the char * doesn''t point to a valid memory
address, but I''m not sure why this would be hapenning since the
Framework should take care of this for me right?
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