How to Fix Rangeerror in C# In Production

Encountering a rangeerror while working with C#? This guide covers the root cause, provides a working code example, and shows you how to prevent it from recurring.

What Causes RangeError

A RangeError in production in C# occurs when a value falls outside its permitted range. Common triggers include:

• Array or string index out of bounds
• Invalid arguments to built-in functions (negative array sizes, invalid string indices)
• Infinite recursion exceeding the maximum call stack size
• Numeric overflow or underflow in calculations
• Pagination parameters pointing past the end of a collection

How to Fix It

// Safe range operations in C#
public static string SafeSubstring(
    string input, int start, int length)
{
    if (string.IsNullOrEmpty(input)) return string.Empty;
    start = Math.Clamp(start, 0, input.Length);
    length = Math.Min(length, input.Length - start);
    return length > 0 ? input.Substring(start, length) : string.Empty;
}

// Safe list access
public static T SafeGet<T>(IList<T> list, int index, T fallback)
{
    if (index >= 0 && index < list.Count) return list[index];
    return fallback;
}

Use Math.Clamp to constrain values to valid ranges and provide typed safe accessor methods.

Prevention Strategies

• Validate all numeric inputs at API boundaries before they reach internal logic
• Add depth limits to recursive algorithms as a safety net
• Use safe accessor methods that return null/None/Option instead of throwing
• Add upper bounds to user-supplied size parameters to prevent resource exhaustion

Catch RangeErrors before they hit production with [Bugsly](https://bugsly.dev) — get full stack traces and the exact value that was out of range for every error in your C# app.