1、最近做项目遇到，C#调用C++dll里的函数需要传递结构体参数，发现这个并不是简单的在C#里定义相应的结构体就可以的，下面以一个例子来说明解决的办法，C++中的函数和结构体如下：
uint msec_set_igr_gen_cfg(int port, IGR_GEN_T *igr_gen)
{
return 0;
}
typedef struct {
int aa_disable; /*/< authentiation adjust checking disable */
int badtag_rej; /*/< reject packet if it is bypassed due to badtag */
int pad_en; /*/< pad non-rejected packets up to 64B */
int byp_ctl_sl; /*/< bypass packet if SL field does not correspond to packet len */
int byp_ctl_v; /*/< bypass packet if V bit is set */
int byp_ctl_sc; /*/< bypass packet if SC bit and either ES or SCB bits are set */
int byp_ctl_ec; /*/< bypass packet if DC bits are not 00 or 11 */
int sectag_flag; /*/< select which flag bit indicates that a SEC tag was present in pkt */
} IGR_GEN_T;
在C#中 首先需要使用Dllimport将相应的C++dll load进来，然后定义相应的结构体，具体如下：
[DllImport("..\\debug\\mgd_MacSec.dll")]
private static extern UInt32 msec_set_igr_gen_cfg(int port, IntPtr igr_gen);
结构体定义：
[StructLayout(LayoutKind.Sequential)]
public class IGR_GEN_T
{
int aa_disable; /*/< authentiation adjust checking disable */
int badtag_rej; /*/< reject packet if it is bypassed due to badtag */
int pad_en; /*/< pad non-rejected packets up to 64B */
int byp_ctl_sl; /*/< bypass packet if SL field does not correspond to packet len */
int byp_ctl_v; /*/< bypass packet if V bit is set */
int byp_ctl_sc; /*/< bypass packet if SC bit and either ES or SCB bits are set */
int byp_ctl_ec; /*/< bypass packet if DC bits are not 00 or 11 */
int sectag_flag; /*/< select which flag bit indicates that a SEC tag was present in pkt */
public IGR_GEN_T()
{
aa_disable = 0;
badtag_rej = 0;
pad_en = 0;
byp_ctl_ec = 0;
byp_ctl_sc = 0;
byp_ctl_sl = 0;
byp_ctl_v = 0;
sectag_flag = 0;
}
} ;
在代码中具体引用函数时如下所示，
IntPtr ptr = Marshal.AllocHGlobal(Marshal.SizeOf(igr_gen));
Marshal.StructureToPtr(igr_gen, ptr, false);
UInt32 ret = _msec_set_igr_gen_cfg(port, ptr);
igr_gen = (IGR_GEN_T)Marshal.PtrToStructure(ptr, typeof(IGR_GEN_T));
Marshal.FreeHGlobal(ptr);
return ret;
从以上步骤可以看出，结构体参数的传递需要marshal做辅助做相应的转化，以intptr的方式传输结构体参数。
2、还存在另外一种情况，是结构体中嵌套有结构体时需要做一些特殊处理，具体如下：
结构体
typedef struct {
int ctx_num; /*/< Index to the context to use */
int sec_level; /* < Security Level to validate frames per context based */
int drop_maxpn; /* < Enable packet drop when max pn is reached for this context>*/
int drop; /*/< Drop this Packet */
int redir; /*/< For Egress, redirect the packet to ingress path (NDL). For Ingress, redirect the packet to alternate destination. */
int auth_en; /*/< Encapsulate and authenticate this packet. */
int enc_en; /*/< Encrypt this packet. auth_en must also be set when this bit is set. (Valid only for egress path). */
} ACT_FLD;
typedef struct {
ACT_FLD *lk_act_fld; /*/< Action to take for an entry within a port */
} LKUP_T;
C++ 函数
uint msec_port_set_egr_entry (IN int port, IN int ent_num, IN LKUP_T *egr_lkup)
{
//
}
C#在调用时首先将相应dll import进来，进行相应结构体的定义和相应函数的声明，具体如下：
[DllImport("..\\debug\\mgd_MacSec.dll")]
private static extern UInt32 msec_set_igr_gen_cfg(int port, IntPtr igr_gen);
[StructLayout(LayoutKind.Sequential)]
public class ACT_FLD
{
public int ctx_num; /*/< Index to the context to use */
public int sec_level; /* < Security Level to validate frames per context based */
public int drop_maxpn; /* < Enable packet drop when max pn is reached for this context>*/
public int drop; /*/< Drop this Packet */
public int redir; /*/< For Egress, redirect the packet to ingress path (NDL). For Ingress, redirect the packet to alternate destination. */
public int auth_en; /*/< Encapsulate and authenticate this packet. */
public int enc_en; /*/< Encrypt this packet. auth_en must also be set when this bit is set. (Valid only for egress path). */
public ACT_FLD()
{
ctx_num = 0;
sec_level = 0;
drop_maxpn = 0;
drop = 0;
redir = 0;
auth_en = 0;
enc_en = 0;
}
}
[StructLayout(LayoutKind.Sequential)]
public class LKUP_T
{
public IntPtr lk_act_fld;
public LKUP_T()
{
ACT_FLD lk_act_fld_s = new ACT_FLD();
lk_act_fld = Marshal.AllocHGlobal(Marshal.SizeOf(lk_act_fld_s));
Marshal.StructureToPtr(lk_act_fld_s, lk_act_fld, false);
}
}
具体在代码中引用时如下所示：
IntPtr egr_lkup_ptr = Marshal.AllocHGlobal(Marshal.SizeOf(egr_lkup));
Marshal.StructureToPtr(egr_lkup, egr_lkup_ptr, false);
uint ret = _msec_port_set_egr_entry(port, ent_num, egr_lkup_ptr);
egr_lkup = (LKUP_T)Marshal.PtrToStructure(egr_lkup_ptr, typeof(LKUP_T));
Marshal.FreeHGlobal(egr_lkup_ptr);
另外枚举（enum）参数传递时类似于int型，只需在C#里定义相应的枚举提即可，不需做相应转化，在此不再给出具体方法。
另，C++ dll要想被C#所使用，需要进行设置，支持通用语言，具体如下图所示：（Common Language Runtime support选项）
关于跨语言之间的结构体参数传输问题，不知是否还有其他比较简洁的办法，欢迎大家讨论，小弟初学C#和.NET，还请大家多多指教。