How to properly add or modify element of a struct array?

New comment
 

Hi! I'm pretty new to programming and trying out the following code. It works for an int array but not on struct array. Maybe it will work if I check for the specific member of the struct like a[iLast].mInt != NULL on the check at the Add1DArrElem (the line with comment // illegal operation error here) function definition but then the whole function will be specific to this struct definition. I wanted to create a function I could reuse on other arrays of any type including struct. Is there already a library predefined with such functions (for mql4)? Or is there a better way of doing this altogether?

/*
*  Array Functions
*/

// Modify Element of an Array
template <typename T>
void Mod1DArrElem(T& a[], int i, T element){
   a[i] = element;
}


// Add Element to Array 
template <typename T>
void Add1DArrElem(T& a[], T element){
   int iLast = ArraySize(a)-1;
   if (a[iLast] != NULL){ // illegal operation error here
      ArrayResize(a, ArraySize(a)+1, 10);
   }
   for (int i=0; i<ArraySize(a); i++){
      if (a[i] != NULL){continue;}
      Mod1DArrElem(a, i, element);
      break;
   }
}


struct SStruct
  {
      int      mInt;
      string   mString;
      
      SStruct(){
         mInt     = NULL;
         mString  = NULL;
      }
      ~SStruct(){}
  };


void OnStart(){
   SStruct StructArr[];
   int s = ArraySize(StructArr);
   PrintFormat("initial size = %i", s);
   ArrayResize(StructArr, 5);
   s = ArraySize(StructArr);
   PrintFormat("after resize size = %i", s);
   for (int x=0; x<s; x++) {
      StructArr[x].mInt = x+1;
      StructArr[x].mString = "Initial Value";
   }
   // Confirm initial Data set
   for (int i=0; i<s; i++){
      PrintFormat("Current StructArr[%i].mInt = %i, StructArr[%i].mString = %s", i, StructArr[i].mInt, StructArr[i].mString);
   };

   // Define Sample Struct Element to add
   SStruct newElem;
   newElem.mInt      = 1000;
   newElem.mString   = "New element";

   // Add struct element using function defined above
   Add1DArrElem(StructArr, newElem);
      
   // Check if element addition was successful
   s = ArraySize(StructArr);
   PrintFormat("After adding element size = %i", s);
   for (int i=0; i<s; i++){
      PrintFormat("Current StructArr[%i].mInt = %i, StructArr[%i].mString = %s", i, StructArr[i].mInt, StructArr[i].mString);
   };
   


// Try with int array (This works)

//   int arr[] = {1,2,3,4,5};
//   
//   // Confirm initial data set
//   int s = ArraySize(arr);
//   PrintFormat("initial size = %i", s);
//   for (int i=0; i<s; i++){
//      PrintFormat("Current arr[%i] = %i", i, arr[i]);
//   };
//   
//   // Add int element using function defined above
//   Add1DArrElem(arr, 10);  
//
//   // Check if element addition was successful
//   s = ArraySize(arr);
//   PrintFormat("final size = %i", s);
//   for (int i=0; i<s; i++){
//      PrintFormat("Current arr[%i] = %i", i, arr[i]);
//   };
//   

}
 
You cannot compare a struct to NULL.

You would need a comparison struct element as replacement of NULL.

Since you are using a constructor in the struct, you could replace NULL with a local struct variable, representing an empty element to be compared to your array element.
 
Thank you very much. I'll try your suggestion.
 

Did you try overloading the == operator?

bool operator== (const SStruct &op) { return this.mInt==op.mInt && this.mString==op.mString; }
bool operator!= (const SStruct &op) { return this.mInt!=op.mInt || this.mString!=op.mString; }
bool operator== (int i) { return this.mInt==i; } // ==NULL goes here
bool operator!= (int i) { return this.mInt!=i; } // !=NULL goes here
New comment