In C#, both string and StringBuilder are used to handle sequences of characters but they behave very differently behind the scenes. Choosing the right one affects performance, memory usage and code clarity especially in loops or high-frequency updates.
🧠 Key Differences
Feature | String | StringBuilder |
|---|---|---|
Mutability | ❌ Immutable | ✅ Mutable |
Memory Allocation | Each change creates a new object in memory | Same object is reused |
Thread-Safety | ✅ Safe | ❌ Not thread-safe by default |
Speed in Loops | ❌ Slow (recreates strings repeatedly) | ✅ Fast (modifies buffer directly) |
Features & Simplicity | ✅ Simple to use, many built-in methods | ❌ Fewer methods, more manual |
Use Case | Small, rarely-changing texts | Large, frequently updated texts |
Null Assignment | ✅ Can be null | ❌ Cannot be null after initialization |
📦 Memory and Performance
stringis stored in memory as an immutable object. Every time you change it, a new object is created. This leads to memory pressure and garbage collection overhead in intensive operations.StringBuilderstores characters in a buffer. Appending or modifying text happens in-place without creating a new object each time.
📋 Example Comparison
Using string:
string colors;
colors += "red";
colors += "blue";
colors += "green";
Each += line creates a brand new string in memory. That means 3 new allocations.
Using StringBuilder:
StringBuilder sb = new StringBuilder();
sb.Append("red");
sb.Append("blue");
sb.Append("green");
string colors = sb.ToString();
All operations modify the same buffer, making it ideal inside loops or when building long strings.
🧪 When to Use What
Use string when:
Your text changes infrequently
You prefer simplicity over performance
You’re working with small text values
Use StringBuilder when:
You need to manipulate large text blocks
You’re appending strings in a loop
You want better performance with fewer memory allocations
Choosing the right tool for the job makes a huge difference in code quality and efficiency.