String vs StringBuilder .NET (C#)

Hi, everyone!

Do you have any use cases to manipulate large strings? Have you ever wondered about optimizing your code? Let's explore the difference between the native string and the string builder. When should we use string builder? When could we use string manipulation directly? My premise is we should use the string builder when we have large string manipulation, and we can use string manipulation directly if we combine two or three strings.

Speed/Performance and Memory

I ran the Benchmark using .NET 8 and BenchmarkDotNet. The result may vary depending on your machine. My machine specs:

1. Intel Core i7-9750H CPU @ 2.60GHz, 6 Core(s), 12 Logical Processor(s)
2. RAM 32 GB, 2667 MHz

The Result

This is the raw result after running my Benchmark. I will explain case by case.

Method	N	Mean	Error	StdDev	Median	Rank	Gen0	Gen1	Gen2	Allocated
AppendWithStringBuilder	1000	10.45 us	0.207 us	0.548 us	10.20 us	1	8.7585	0.9613	-	53.91 KB
AppendWithStringBuilder	10000	213.85 us	4.248 us	7.768 us	212.04 us	2	66.6504	66.6504	66.6504	435.63 KB
AppendWithString	1000	759.31 us	15.032 us	20.068 us	756.16 us	3	1755.8594	93.7500	-	10777.3 KB
PrependWithString	1000	761.74 us	15.045 us	25.137 us	761.18 us	3	1755.8594	93.7500	-	10777.3 KB
AppendWithStringBuilder	100000	1,491.00 us	8.566 us	7.153 us	1,493.93 us	4	707.0313	652.3438	353.5156	4316.28 KB
PrependWithStringBuilder	1000	3,652.40 us	57.881 us	51.310 us	3,639.86 us	5	19.5313	3.9063	-	123.07 KB
PrependWithString	10000	103,185.42 us	1,756.825 us	1,643.335 us	102,605.36 us	6	316200.0000	294200.0000	290200.0000	1074665.57 KB
AppendWithString	10000	103,766.99 us	2,047.758 us	2,102.896 us	103,956.12 us	6	316200.0000	294200.0000	290200.0000	1074665.57 KB
PrependWithStringBuilder	10000	443,622.50 us	8,848.754 us	9,087.019 us	443,266.50 us	7	-	-	-	1230.88 KB
AppendWithString	100000	31,694,035.38 us	479,131.423 us	424,737.527 us	31,537,399.50 us	8	18852000.0000	18809000.0000	18805000.0000	107431164.26 KB
PrependWithString	100000	32,527,484.53 us	133,803.969 us	111,732.374 us	32,527,375.30 us	9	19962000.0000	19918000.0000	19914000.0000	107431463.44 KB
PrependWithStringBuilder	100000	58,193,475.60 us	712,873.020 us	792,356.472 us	58,134,526.30 us	10	1000.0000	-	-	12305.1 KB

Append Case

Method	N	Mean	Error	StdDev	Median	Rank	Gen0	Gen1	Gen2	Allocated
AppendWithStringBuilder	1000	10.45 us	0.207 us	0.548 us	10.20 us	1	8.7585	0.9613	-	53.91 KB
AppendWithString	1000	759.31 us	15.032 us	20.068 us	756.16 us	3	1755.8594	93.7500	-	10777.3 KB
AppendWithStringBuilder	10000	213.85 us	4.248 us	7.768 us	212.04 us	2	66.6504	66.6504	66.6504	435.63 KB
AppendWithString	10000	103,766.99 us	2,047.758 us	2,102.896 us	103,956.12 us	6	316200.0000	294200.0000	290200.0000	1074665.57 KB
AppendWithStringBuilder	100000	1,491.00 us	8.566 us	7.153 us	1,493.93 us	4	707.0313	652.3438	353.5156	4316.28 KB
AppendWithString	100000	31,694,035.38 us	479,131.423 us	424,737.527 us	31,537,399.50 us	8	18852000.0000	18809000.0000	18805000.0000	107431164.26 KB

As you can see, the String Builder always wins. It's not only in terms of performance but also allocated memory. The ratio of performance and memory is high. You know, it's a big deal!

If you wonder why the string concat uses large memory when looping, it will copy the string N times. The string is immutable, so they need to copy the content.

Append String Builder

Append String

Prepend Case

Method	N	Mean	Error	StdDev	Median	Rank	Gen0	Gen1	Gen2	Allocated
PrependWithString	1000	761.74 us	15.045 us	25.137 us	761.18 us	3	1755.8594	93.7500	-	10777.3 KB
PrependWithStringBuilder	1000	3,652.40 us	57.881 us	51.310 us	3,639.86 us	5	19.5313	3.9063	-	123.07 KB
PrependWithString	10000	103,185.42 us	1,756.825 us	1,643.335 us	102,605.36 us	6	316200.0000	294200.0000	290200.0000	1074665.57 KB
PrependWithStringBuilder	10000	443,622.50 us	8,848.754 us	9,087.019 us	443,266.50 us	7	-	-	-	1230.88 KB
PrependWithString	100000	32,527,484.53 us	133,803.969 us	111,732.374 us	32,527,375.30 us	9	19962000.0000	19918000.0000	19914000.0000	107431463.44 KB
PrependWithStringBuilder	100000	58,193,475.60 us	712,873.020 us	792,356.472 us	58,134,526.30 us	10	1000.0000	-	-	12305.1 KB

As you can see, the String Builder starts struggling after dealing with prepend. I will choose String Builder if I have memory concerns. Of course, there is a tread-off. I rarely do prepend the string. If needed to do so, I might choose a different approach.

If you need to learn more about the difference between String and String Builder, please visit this documentation.

Prepend String Builder

Prepend String

Benchmark Code

bervProject / StringBuilderPerformance

String Builder Performance

StringBuilderPerformance

String Builder Performance

Summary

Method	N	Mean	Error	StdDev	Median	Rank	Gen0	Gen1	Gen2	Allocated
AppendWithStringBuilder	1000	10.45 us	0.207 us	0.548 us	10.20 us	1	8.7585	0.9613	-	53.91 KB
AppendWithStringBuilder	10000	213.85 us	4.248 us	7.768 us	212.04 us	2	66.6504	66.6504	66.6504	435.63 KB
AppendWithString	1000	759.31 us	15.032 us	20.068 us	756.16 us	3	1755.8594	93.7500	-	10777.3 KB
PrependWithString	1000	761.74 us	15.045 us	25.137 us	761.18 us	3	1755.8594	93.7500	-	10777.3 KB
AppendWithStringBuilder	100000	1,491.00 us	8.566 us	7.153 us	1,493.93 us	4	707.0313	652.3438	353.5156	4316.28 KB
PrependWithStringBuilder	1000	3,652.40 us	57.881 us	51.310 us	3,639.86 us	5	19.5313	3.9063	-	123.07 KB
PrependWithString	10000	103,185.42 us	1,756.825 us	1,643.335 us	102,605.36 us	6	316200.0000	294200.0000	290200.0000	1074665.57 KB
AppendWithString	10000	103,766.99 us	2,047.758 us	2,102.896 us	103,956.12 us	6	316200.0000	294200.0000	290200.0000	1074665.57 KB
PrependWithStringBuilder	10000	443,622.50 us	8,848.754 us

…

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Thank you

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