Iterate Over Struct; Easily Display Struct Fields And Values In a RichEdit Box

Question

Is there an easier way to display the struct fields and their corresponding values in RichEdit control?

This is what I am doing now:

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Answer 1

There is no way to iterate the members of a struct unless you build your own metadata to describe the struct. The C++ compiler simply doesn't emit the information you would need automatically.

However, with a bit of macro magic, you can build the metadata you would need pretty easily. I wrote some code to do this (actually a full blown Windows custom control) many years ago and I still use it all the time.

The basic trick is to use a bit macro magic of get the compiler to help you build the metadata.

// this is the structure I want to iterate
typedef struct {
   int foo;
   char bar[16];
} StructIWantToIterate;

// this is the metadata I need for each field of the structure
typedef struct {
   char * pszFieldName;
   size_t oFieldOffset;
   size_t cbFieldSize;
   int    eType;
} MyStructMeta;

// these are the field types I need to handle.
enum {
  type_is_int,
  type_is_char,
};

// these macros help to emit the metadata
#define NUMELMS(ary)     (sizeof(ary)/(sizeof(ary)[0]))
#define FIELDOFF(tag,fld)  ((size_t)&(((tag *)0)->fld))
#define FIELDSIZ(tag,fld)  sizeof(((tag *)0)->fld)
#define STDFLD(tag,fld,as)  #fld, FIELDOFF(tag,fld), FIELDSIZ(tag,fld), as

// now we declare the metadata for the StructIWantToIterate structure
#undef MYFLD
#define MYFLD(fld,as) STDFLD(StructIWantToIterate,fld,as)
static const MyStructMeta aMeta[] = {
   MYFLD(foo, type_is_int), // expands to "foo", 0, sizeof(int), type_is_int
   MYFLD(bar, type_is_char),// expands to "bar", sizeof(int), 16, type_is_char
};

// and when we want to do the iteration,  assume ptr is a pointer to an instance
// of StructIWantToIterate

for (int ii = 0; ii < NUMELMS(aMeta); ++ii)
{
   char szLine[100]; // pick your own worst case line size.

   // get a pointer to the current field within the struct
   void * pfld = ((byte*)ptr) + aMeta[ii].oFieldOffset;

   // print out the field data based on the type_is_xxx information
   switch (aMeta[ii].eType)
   {
      case type_is_int:
         sprintf(szLine, "%s : %d", aMeta[ii].pszFieldName, *(int*)pfld);
         break;

      case type_is_char:
         sprintf(szLine, "%s : %*s", 
                aMeta[ii].pszFieldName, 
                aMeta[ii].cbFieldSize, 
                pfld);
         break;
   }
   // send it to the richedit control
   RichEdit1->Lines->Append(asLine);    
}