What exactly does these associative array method does? next,prev

SystemVerilog
, ,
1

next(var) assigns the value of next index to the variable var
prev(var) assigns the value of previous index to the variable var

array='{"apple:1,"guava:4","orange":5,"grapes":7}
string k = "guava";
array.prev(k)-> apple
array.next(k)-> guava

Does it need to give apple and orange respectively for prev and next
else
the output is correct .why?

2

In reply to Kishankk:

You quoted the LRM incorrectly.

The next() method finds the smallest index whose value is greater than the given index argument.
The prev() method finds the largest index whose value is smaller than the given index argument.

int array='{"apple":1,"guava":4,"orange":5,"grapes":7}
string k = "guava";]
int c;
initial begin
      c = array.prev(k); // k becomes "grapes"
      c = array.next(k); // k becomes "guava"
end
3

Hi Dave,

Thanks for the reply.
EDA Link: Associative array - EDA Playground

fruits= '{“apple”:6,“orange”:2, “guava”:3, “watermelon”: 9,“grape”:1};
//OUTPUT//
Previous fruit of guava is [grape] = 1
Next fruit of guava is [guava] = 3

My understandings.
index of apple=0,
index of orange=1,
index of guava=2,
index of watermelon=3,
index of grape=4,

The next() method finds the smallest index whose value is greater than the given index argument.
=> value greater than guava’s(3) :apple(6),watermelon(9) but here smallest index is apple

The prev() method finds the largest index whose value is smaller than the given index argument.
=> value smaller than guava’s(3):grape(1),orange(2) but largest index is grape.

Let me know if my understanding is correct.

If my understanding is correct then output is wrong.

4

In reply to Kishankk:

first() returns the smallest index, which is “apple”. last() returns the largest index, which is “watermelon”.

The next() method finds the smallest index whose value is greater than the given index argument. “apple” is not greater than “guava”.

5

Sorry Dave, I didn’t understand.
Can you elaborate more on this.

6

In reply to Kishankk:

Hi ,
I believe this scenario is similar to 2D vector with string-index in C++.
Here the strings are apple, orange, guava, watermelon, and grape.
Now in order to get a clear understanding of what is happening in that code, we need to look at these strings in sorted order. After sorting these strings, we get-

apple
grape
guava
orange
watermelon

If you analyze this answer, you’ll see that watermelon got the last place because its length is the highest. Then orange. Rest are arranged based on the ASCII values of each and every letter because they have the same length.

Go through this code for a better understanding.


// Associative array //
module associative_array();

  int fruits[string];  
  initial begin
    
    fruits= '{"apple":6,"orange":2, "guava":3, "watermelon": 9,"grape":1};
    begin
      string  f; // Default value of f would be lowest index i.e. "apple"
      while(fruits.next(f))
        $display(" Next fruit of is [%s] = %0d",f,fruits[f]);//It'll stop as it's not cyclic in nature unlike enum
    end
  end
endmodule


//ANSWER
# Loading sv_std.std
# Loading work.associative_array(fast)
# 
# vsim -voptargs=+acc=npr
# run -all
#  Next fruit of is [apple] = 6
#  Next fruit of is [grape] = 1
#  Next fruit of is [guava] = 3
#  Next fruit of is [orange] = 2
#  Next fruit of is [watermelon] = 9
# exit
# End time: 11:02:46 on Feb 27,2023, Elapsed time: 0:00:01
# Errors: 0, Warnings: 0