C#代码到C世界函数的调用

我有点怀疑，
我正在从C#托管世界到C托管代码库进行函数调用.
C#代码

I have small doubt,
I am having function call from C# managed world to C unmanaged code base..

C# Code

Boolean ChsarpFunction(StringBuilder sb) {
int size;

return GetFormattedString(sb,size);
}

[DllImport(MYDLL, CharSet = CharSet.Auto, SetLastError = true, BestFitMapping = false)]
[return: MarshalAs(UnmanagedType.U1)]
... Boolean GetFormattedString( [MarshalAs(UnmanagedType.LPStr)] StringBuilder value, int size);

C代码
bool GetFormattedString(字符* str，整数*大小){
..
..
strcpy(str，result);
* size = strlen(str);
return(* size> 0); //0或1的某些结果
}

我不知道或不想设置StringBuilder的大小，哪种类型的字符串最适合通过引用传递.(性能明智) 任何想法或经验都将不胜感激.

谢谢，

C Code
bool GetFormattedString (char *str, int* size) {
..
..
strcpy(str,result);
*size = strlen(str);
return (*size > 0); // some result of 0 or 1
}

I don''t know or want to set the size for the StringBuilder, What kind of string is optimal to pass by reference.(performance wise)
Any ideas or experience is much appreciated.

Thanks,