Question

I am creating scripting language.
When I allocate thing ,it’s allocate the thing and returns the address
and then I do whatever with it and then delete it. I can’t control the variables in it
like creating struct in my lang (Struct with pointer and bool to check if pointer is pointing to valid data) and etc because it’ll make my lang slower and bigger in the RAM.

For example: (My scripting language is easily to understood. I doubt you’ll not understand this ,but I’ll put some comments in it anyway)

MyStruct = { //Function. For create object with it use 'new' before it.
    TestAliveVar=0
}
Func = { //I'll explain what exactly this function does every place it runs.
    if (!exists(arg0)) //C++: ???
        exit;
    arg0.TestAliveVar=1
    println "Still alive!";
}
var MyVar=new MyStruct(); //Returns address of the new object in the heap
                          //and runs on it the `MyStruct` function.
Func(MyVar);              //Sets his 'TestAliveVar' to 1
                          //and prints 'Still Alive!' with new line
delete(MyVar);            //C++: free(MyVar);
Func(MyVar);              //Does nothing

The question is how to create the function exists you saw in this code.
BTW I can run C++ codes in this lang.

Answer 1

This valid check checked in windows only (VS),here is the function:

#pragma once
//ptrvalid.h
__inline bool isValid(void* ptr) {
    if (((uint)ptr)&7==7)
        return false; //Not valid address at all (Maybe random pointer?)
    char _prefix;
    __try {
        _prefix=*(((char*)ptr)-1); //Get the prefix of this data
    } __except (true) { //Catch all unique exceptions (Windows exceptions) 
        return false; //Can't reach this memory
    }
    switch (_prefix) {
    case 0:    //Running release mode with debugger
    case -128: //Running release mode without debugger
    case -2:   //Running debug mode with debugger
    case -35:  //Running debug mode without debugger
        return false; //Deleted :(
        break;
    }
    return true; //Still alive!
}

Usage:

#include <stdio.h>
#include "ptrvalid.h"

void PrintValid(void* ptr) {
    if (isValid(ptr))
        printf("%d is valid.\n",ptr);
    else
        printf("%d is not valid.\n",ptr);
}

int main() {
    int* my_array=(int*)malloc(4);
    PrintValid(my_array);
    PrintValid((void*)99);
    free(my_array);
    PrintValid(my_array);
    my_array=new int[4];
    PrintValid(my_array);
    delete my_array;
    PrintValid(my_array);
    getchar();
}

Output:

764776 is valid.
99 is not valid.
764776 is not valid.
774648 is valid.
774648 is not valid.

Function’s explanation: (What it does)

The functions check before the real checking ,if the address is valid\start point to memory.
After that he checks if this process can reach this memory’s prefix (If caught exception if can’t) and the last checking is checking what the prefix of this memory if deleted at any mode. (Debugging\Without Debug Mode\Release Mode)
If the function passed all of those checks ,it returns true.