How to define a const structure variable

bigbat

How to define a const structure variable [Copy link]

I have defined a structure and I want all definitions to be placed in the code area instead of RAM memory.

typedef struct 
{
   const int id;
   const char *name;
   struct NodeType *Link;
}NodeType;


const char* str1="tom";

NodeType node1,node2,node3;

main{
        node1.id = 1;
		node1.name = str1;
}

All definitions are fine, but it fails when initializing node1.id = 1; The compiler used is keil 5

lcofjp

const NodeType node1={0, "tom", &node2};

It should be like this, and it should be initialized when declared. Unused members do not need to be specified as const.

Since you want to put it in the constant area, it is impossible to initialize it in the main function

w494143467

If you have a const type in your structure, you need to initialize it when you create it, just like the above.

bigbat

const typedef struct 
{
   const int  id;
	 const char *name;
	 const struct NodeType *Link;
}NodeType;

/*=====================================*/


const  NodeType node3={2,"",NULL};
const  NodeType	node2={1,"jack",&node3};
const  NodeType node1={0,"tom",&node2};

Thank you very much. I just tried it and only const NodeType node3={2,"",NULL}; works. The others cannot be compiled.

bigbat

I thought it was a problem with the symbol &node3, but it seems not.

It seems that pointers cannot be used in structures???

bigbat

lcofjp posted on 2021-7-9 12:39 const NodeType node1={0, "tom", &node2}; It should be like this, and it should be initialized when declared. There is no need inside...

It seems that pointers cannot be used.

#144: a value of type "NodeType *" cannot be used to initialize an entity of type "const struct NodeType *"

lcofjp

Because the syntax of the structure you defined is incorrect, I didn't mention it above so I thought it was a typo in your post.

typedef struct _NodeType
{
   const int id;
   const char *name;
   struct _NodeType *Link;
}NodeType;

freebsder

const needs to be initialized