MQL4 Truncate Double with NormalizeDouble

Truncating Doubles with NormalizeDouble in MQL4

In MQL4, the NormalizeDouble function is used to round or truncate a double value to a specified number of decimal places. This is crucial in trading applications to ensure price or pip values align with broker precision requirements, avoiding calculation errors.

Key Concepts

• double: A data type for decimal numbers (e.g., 123.45678).
• NormalizeDouble: Adjusts a double value to a specified precision.
• Truncation vs. Rounding: Truncation cuts off excess decimals without rounding up or down.

Example Code

void OnStart()
{
   double number = 123.45678;
   double truncated = TruncateDouble(number, 2);
   Print("Original: ", number, " | Truncated: ", truncated); // Output: Original: 123.45678 | Truncated: 123.45
}

double TruncateDouble(double value, int digits)
{
   // NormalizeDouble rounds, so we use a trick to truncate
   double multiplier = MathPow(10, digits);
   double truncated = MathFloor(value * multiplier) / multiplier;
   return NormalizeDouble(truncated, digits);
}
            

Explanation

1. Input: Start with a double value, e.g., 123.45678.
2. Multiplier: Multiply by 10^digits (e.g., 100 for 2 decimals) to shift the decimal point.
3. MathFloor: Use MathFloor to truncate by removing the fractional part after shifting (e.g., 12345.678 becomes 12345).
4. Divide Back: Divide by the multiplier to restore the decimal position (e.g., 12345 / 100 = 123.45).
5. NormalizeDouble: Ensure the result adheres to the specified precision (e.g., 123.45).

Why Use NormalizeDouble?

NormalizeDouble ensures the double value matches the precision expected by MetaTrader (e.g., 4 or 5 digits for forex pairs), preventing floating-point errors in calculations like lot sizes or stop losses.

Try It Yourself

Copy the code into MetaTrader 4's MetaEditor, compile it, and run it in a script to see the result in the Experts tab.