如何在另一个结构中访问结构

Question

I have the following struct arrangement, and I'mstruggling to get the data contained within the first myNestedStruct part of the data.

struct myNestedStruct
{
    char programName[28];          

    union
    {
        float parameters[1];        
        struct
        {
            long size;      
            char info[1];      
        } datas;                 
    } contents;                  

} myNestedStruct;

struct myStruct
{    
    int ID;             
    int numIDs;        

    union
    {        
        myNestedStruct programs[1]; 

        struct        
        {
            int size;                
            char info[1];   

        } datas;                    

    } contents;                         
};

Should I be accessing it like this:

myStruct.contents.programs[0].contents.datas

Answer 1

Your definitions are not consistent.

Either use named structs, and only named structs:

struct MyNestedStruct /* note: no typedef, but a name */
{
  char programName[28];          

  union
  {
    float parameters[1];        
    struct
    {
      long size;      
      char info[1];      
    } datas;                 
  } contents;                  
};

struct MyStruct /* note: no typedef, but a name */
{    
  int ID;             
  int numIDs;        

  union
  {        
    struct MyNestedStruct programs[1]; /* note the struct */

    struct        
    {
      int size;                
      char info[1];   

    } datas;                    
  } contents;                         
};

Then define a variable like this:

struct MyStruct myStruct;

myStruct.contents.programs[0].contents.datas ...;

or use typedef'ed anonymous structs, and only typedef'ed anonymous structs:

typedef struct /* note: typedef, but NO name */
{
  char programName[28];          

  union
  {
    float parameters[1];        
    struct
    {
      long size;      
      char info[1];      
    } datas;                 
  } contents;                  
} MyNestedStruct;

typedef struct /* note: typedef, but NO name */
{    
  int ID;             
  int numIDs;        

  union
  {        
    MyNestedStruct programs[1]; /* NO struct, as typedef'ed above */

    struct        
    {
      int size;                
      char info[1];   

    } datas;                    
  } contents;                         
} MyStruct;

Then define a variable like this:

MyStruct myStruct;

myStruct.contents.programs[0].contents.datas ...;

You could mix these two approaches, but doing so just leads to confusion.

Answer 2

Structure syntax is

struct [structure tag] {

   member definition;
   member definition;
   ...
   member definition;
} [one or more structure variables];  

Here structure tag is optional.

so changes in your code are

struct myNestedStruct
{
    char programName[28];          

    union
    {
        float parameters[1];        
        struct
        {
            long size;      
            char info[1];      
        } datas;                 
    } contents;                  

} ;  //Removed variable

struct myStruct
{    
    int ID;             
    int numIDs;        

    union
    {        
        struct myNestedStruct programs[1]; //Added struct keyword

        struct        
        {
            int size;                
            char info[1];   

        } datas;                    

    } contents;                         
} var;  //Declared variable

How to access struct inside another struct

var.contents.programs[0].contents.datas.size = 10 ;  //e.g use according to your need