Why do I get a syntax error using the ternary operator with function calls?

Question

I'm writing a code in SystemVerilog, and I'm trying to use the ternary operator to decide between two function calls. Here's my code:

module tb;
  int a = 1, b = 4;
  initial begin
    b > a ? $display("%0d", b) : $display("Value: %0d", a); // Syntax error
    $display("%0d", b > a ? b : a); // This works correctly
  end
endmodule

In the line b > a ? print(b) : print(a);, I get a syntax error, but the line print(b > a ? b : a); works perfectly. I don’t understand why using the ternary operator directly with function calls causes a syntax error.

Can someone explain why this happens and how to fix it?

toolic · Accepted Answer · 2024-09-15 11:19:25Z

1

The function calls are not the cause of the syntax error. The problem is that the ?: construct is simply an operator; it is not a complete statement by itself. You would still get a syntax error with the following code for example:

b > a ? b : a;

There are no function calls in that line. You would get the same syntax error with any operator, such as:

a || b;

To call a function based on a condition, you should use the if/else procedural code:

module tb;
  int a = 1, b = 4;
  initial begin
    if (b > a)
        $display("%0d", b);
    else
        $display("Value: %0d", a);
  end
endmodule

answered Sep 15, 2024 at 11:19

toolic

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