循环遍历 C 中结构中的元素以提取单个元素的值和数据类型 [英] Looping through elements in a struct in C for extracting value and datatype of the individual element

问题描述

我有一个要求，我有一个由大约 30 多个不同数据类型的不同元素组成的 C 语言结构:

I have a requirement where I have a big structure in C consisting of around more than 30 different elements of different data types:

typedef struct {
  type1 element1;
  type2 element2;
  type3 element3;
  type2 element4[10];
  ...
  typeN elementN;
} my_messg_struct;

这里基本上是通过串行协议发送的消息中的一组元素.该消息具有不同数据类型的各种元素，如上述结构中所捕获.同样，我也有很多其他消息.现在我必须编写一个通用函数，它负责读取这些消息结构并循环读取每个元素的值和数据类型，然后通过串行端口进行传输.我需要先读取数据类型，因为在我的情况下，各种数据类型的传输顺序是不同的.

where this is basically a group of elements in a message sent over the serial protocol. This message has various elements of varying datatypes as captured in the above structure. Similarly, I have a lot of other messages as well. Now I have to write a generic function which is responsible for reading these message structs and loop through each of the elements reading the element's value and datatype and then transmitting over the serial port. I need to read the datatype first because the order of transmission of various datatypes is different in my case.

所以，基本上，我只想知道如何在 C 中循环遍历结构的元素，以便我可以读取结构中存在的每个元素的值和数据类型?

So, basically, I just wanted to know how to loop through elements of a struct in C in such a way that I can read the value and data type of each of the element present in a struct?

推荐答案

您可以尝试使用 X 宏，但由此产生的源代码可读性值得怀疑:

You could try to use X macros, but the resulting source code readability is questionable:

 #include <stdio.h>

 #define LIST_OF_VARIABLES \
     XI(int, value1) \
     XD(double, value2) \
     XU(unsigned, value3)


 #define XI(int, name) int name;
 #define XD(double, name) double name;
 #define XU(unsigned, name) unsigned name;
 typedef struct A {
     LIST_OF_VARIABLES
 } A;
 #undef XI
 #undef XD
 #undef XU

 void print_variables(struct A a)
 {
 #define XI(type, name) printf("%s = %d\n", #type, a.name);
 #define XD(type, name) printf("%s = %f\n", #type, a.name);
 #define XU(type, name) printf("%s = %u\n", #type, a.name);
 LIST_OF_VARIABLES
 #undef XI
 #undef XD
 #undef XU
 }

 int main(void) {
     A a = {
         .value1 = 10,
         .value2 = 0.5,
         .value3 = 1,
     };
     print_variables(a);
     return 0;
 }

既然您在每个 #type 出现处都放置了一个类型字符串，您可以使用一些字符串比较函数来确定每种类型的基础.

Now that you have a type string placed on every #type occurrence you could use some string comparison functions to determine what to based for each type.

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