C＃Pinvoke字符串

Question

我试图使用PInvoke绑定此C函数。

bool GuiTextBox(Rectangle bounds, char *text, int textSize, bool editMode); 

这是PInvoke签名。

[DllImport(nativeLibName,CallingConvention = CallingConvention.Cdecl)]
public static extern bool GuiTextBox(Rectangle bounds, 
                                     string text, 
                                     int textSize, 
                                     bool freeEdit);

当我尝试使用它时，字符串不会被修改。我尝试将它作为ref传递但是当我尝试使用它时，它试图读取或写入受保护的内存时崩溃。

Answer 1

我希望它应该是这样的：

// private : do not expose inner details; 
// we have to manipulate with StringBuilder
[DllImport(nativeLibName,
           CallingConvention = CallingConvention.Cdecl,
           EntryPoint = "GuiTextBox",
           CharSet = CharSet.Unicode)] //TODO: Provide the right encoding here
private static extern bool CoreGuiTextBox(Rectangle bounds, 
                                          StringBuilder text, // We allow editing it
                                          int textSize, 
                                          bool freeEdit);

// Here (in the public method) we hide some low level details
// memory allocation, string manipulations etc.
public static bool CoreGuiTextBox(Rectangle bounds, 
                                  ref string text, 
                                  int textSize, 
                                  bool freeEdit) {
  if (null == text)
    return false; // or throw exception; or assign "" to text

  StringBuilder sb = new StringBuilder(text);  

  // If we allow editing we should allocate enough size (Length) within StringBuilder
  if (textSize > sb.Length)
    sb.Length = textSize;

  bool result = CoreGuiTextBox(bounds, sb, sb.Length, freeEdit);   

  // Back to string (StringBuilder can have been edited)
  // You may want to add some logic here; e.g. trim trailing '\0'  
  text = sb.ToString();

  return result;
}