String Building

Description

Let's assume you need to generate a long string (length 1000) containing the same character. I can think of three ways:

• Use a while loop that appends the character 1000 times to a string variable.
• Use a while loop that appends the character 1000 times to a StringBUilder.
• Use the constructor of the System.String class.

Question

• Which is more performant and what is the difference?

Conclusion

Pretty much what is expected:

• String concatenation is much slower than using StringBuilder.
• String constructor is much quicker than StringBuilder.

Notes

• String constructor, even if it is the most performant, can be used only for a limited range of situations:
  • when the string is created repeating the same character.
• On the other hand StringBuilder is the best universal approach for concatenating any strings, of any lengths.

Measurements

Method	StringLength	Mean	Error	StdDev	Median
Concatenation	100	2,856.07 ns	65.799 ns	274.257 ns	2,803.80 ns
StringBuilder	100	348.44 ns	6.434 ns	26.887 ns	347.03 ns
'String ctor'	100	41.93 ns	1.001 ns	4.118 ns	40.33 ns
Concatenation	1000	104,271.34 ns	929.487 ns	3,811.934 ns	103,092.47 ns
StringBuilder	1000	2,955.03 ns	50.705 ns	211.907 ns	2,937.97 ns
'String ctor'	1000	312.96 ns	6.465 ns	26.073 ns	303.51 ns

See the full benchmark results and logs in the /doc/benchmark-results directory.

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