我正在尝试 PInvoke 一个具有嵌套结构数组指针的结构参数的方法。c 声明如下所示：
duckdb_state duckdb_query(duckdb_connection connection, const char *query, duckdb_result *out_result);
typedef struct {
void *data;
bool *nullmask;
duckdb_type type;
char *name;
} duckdb_column;
typedef struct {
idx_t column_count;
idx_t row_count;
duckdb_column *columns;
char *error_message;
} duckdb_result;
我在 C# 中这样声明它们：
[DllImport("duckdb.dll", CallingConvention = CallingConvention.Cdecl, EntryPoint = "duckdb_query")]
public static extern DuckdbState DuckdbQuery(IntPtr connection, string query, out DuckdbResult result);
[StructLayout(LayoutKind.Sequential)]
public struct DuckdbColumn
{
IntPtr data;
bool nullmask;
DuckdbType type;
string name;
}
[StructLayout(LayoutKind.Sequential)]
public struct DuckdbResult
{
public long column_count;
public long row_count;
public IntPtr columns;
public string error_message;
}
但是当我尝试执行查询并读取列时，我没有得到任何有意义的数据：
result = DuckdbQuery(connection, "SELECT * FROM integers", out queryResult);
DuckdbColumn[] columns = new DuckdbColumn[queryResult.column_count];
var queryResultColumns = queryResult.columns;
var columnPointer = Marshal.ReadIntPtr(queryResultColumns);
var ptrToStructure = (DuckdbColumn)Marshal.PtrToStructure(columnPointer, typeof(DuckdbColumn));
我应该如何更改 PInvoke 声明，以便在执行查询后可以读取列？
在以下位置有示例 c 代码：DuckDB c 示例
更新 1
我可以使用以下代码获取列名：
for (int i = 0; i < queryResult.column_count; i++)
{
var column = (DuckdbColumn)Marshal.PtrToStructure(queryResult.columns + 8 + (Marshal.SizeOf<DuckdbColumn>() + 8) * i, typeof(DuckdbColumn));
columns[i] = column;
}
但type字段仍然说DUCKDB_TYPE_INVALID
更新 2
正如大卫在他的回答中所建议的那样，我改为bool nullmask;现在IntPtr nullmask;可以阅读这样的列信息：
for (int i = 0; i < queryResult.column_count; i++)
{
var column = (DuckdbColumn)Marshal.PtrToStructure(queryResult.columns + Marshal.SizeOf<DuckdbColumn>() * i, typeof(DuckdbColumn));
columns[i] = column;
}