在Python中解压缩嵌套的C结构 [英] Unpacking nested C structs in Python

问题描述

我正在尝试解压缩以二进制形式传递给我的Python程序的C结构，其中包括另一个嵌套结构. C标头的相关部分如下所示:

I am trying to unpack a C struct that is handed to my Python program in binary form and includes another nested struct. The relevant part of the C header looks like this:

typedef struct {
    uint8_t seq;
    uint8_t type;
    uint16_t flags;
    uint16_t upTimestamp;
}__attribute__ ((packed)) mps_packet_header;

typedef struct {
    mps_packet_header header;
    int16_t x[6];
    int16_t y[6];
    int16_t z[6];
    uint16_t lowTimestamp[6];
}__attribute__((packed)) mps_acc_packet_t;
typedef mps_acc_packet_t accpacket_t;

现在，在我的Python程序中，我想使用struct.unpack解压缩accpacket.但是，我不知道解压缩的格式字符串应该是什么，因为accpacket包含嵌套的mps_packet_header.我试过只在开头插入mps_packet_header的格式字符串，然后继续其余的accpacket:

Now, in my Python program, I want to use struct.unpack to unpack an accpacket. However, I don't know what the format string for the unpack should be as the accpacket contains a nested mps_packet_header. I have tried just inserting the format string for the mps_packet_header at the beginning and then continuing with the rest of the accpacket:

s = struct.Struct('= B B H H 6h 6h 6h H')
seq, _type, flags, upTimestamp, x, y, z, lowTimestamp = s.unpack(packet_data)

但是，这显然是不正确的.格式字符串的calcsize为44，而结构本身的大小为54.

However, this is apparently not correct; the format string has a calcsize of 44, while the struct itself has a size of 54.

如何为该结构制定正确的格式字符串?

How do I formulate a correct format string for this struct?

推荐答案

1. 您的Struct格式与C结构不匹配. (最终H应该为6H)
2. struct.unpack(6h，..)确实返回6个字段. (没有一个包含6个元素)

1. You Struct format does not match with C structure. (final H should be 6H)
2. struct.unpack(6h, ..) does return 6 fields. (not one with 6 elements)

因此您的代码应类似于..

So your code should looks like ..

s = struct.Struct('= B B H H 6h 6h 6h 6H')
fields = s.unpack(packet_data)
seq, _type, flags, upTimestamp = fields[:4]
x = fields[4:10]
y = fields[10:16]
z = fields[16:22]
lowTimestamp = fields[22:]

这篇关于在Python中解压缩嵌套的C结构的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！