Don't Use String.Format() to Concatenate Strings
While string-formatting routines built into .NET are very useful for globalization and other tasks, they're not meant to be used for appending strings to each other. Example 7 tests the performance difference between String.Format() and string concatenation.
Use StringBuilder to Build Strings Inside Loops
The StringBuilder class is basically an array list for string fragments; the StringBuilder takes care of expanding its internal char array, hiding this from the user. The use of this class is also specially optimized by the .NET compiler, making it impossible to duplicate this functionality with equivalent performance (for instance, by manipulating char arrays directly and converting to a string afterwards). Example 8 shows the performance benefit of building a large string using StringBuilder instead of string concatenation.
Don't Use StringBuilder to Concatenate Small Numbers of Strings
Many .NET developers who consider themselves well-versed in performance matters advocate the use of the StringBuilder class whenever possible. However, it's not the fastest approach for concatenating small numbers of strings. Actually, any number can be combined in a single statement, although the performance benefit tends to dwindle above five or six substrings. This is due to instantiation and destruction overhead for the StringBuilder instance, as well as method-call overhead involved in calling Append() once for every added substring and ToString() once the string is built. What are the alternatives? Plus-sign concatenation and the String.Concat() method are equivalent; I prefer plus signs for readability. Note that this cannot be used across loops because the entire concatenation must occur within a single statement. Example 9 tests String.Concat() vs. StringBuilder for various numbers of substrings.
Don't Be Afraid to Use String Literals
Many developers incorrectly assume that a new object is created for every string literal, and, therefore, avoid their use. In some cases, using string literals directly in your code is a better approach than using string constants! It can make the code easier to understand and has no adverse impact on performance. This is due to the use of the .NET interned string table; this table maintains a String instance for every known string and reuses this instance whenever the same character sequence is used as a literal. See the documentation of the String.Intern() method for more details. Example 10 compares string literals to the use of string constants.
While string-formatting routines built into .NET are very useful for globalization and other tasks, they're not meant to be used for appending strings to each other. Example 7 tests the performance difference between String.Format() and string concatenation.
Use StringBuilder to Build Strings Inside Loops
The StringBuilder class is basically an array list for string fragments; the StringBuilder takes care of expanding its internal char array, hiding this from the user. The use of this class is also specially optimized by the .NET compiler, making it impossible to duplicate this functionality with equivalent performance (for instance, by manipulating char arrays directly and converting to a string afterwards). Example 8 shows the performance benefit of building a large string using StringBuilder instead of string concatenation.
Don't Use StringBuilder to Concatenate Small Numbers of Strings
Many .NET developers who consider themselves well-versed in performance matters advocate the use of the StringBuilder class whenever possible. However, it's not the fastest approach for concatenating small numbers of strings. Actually, any number can be combined in a single statement, although the performance benefit tends to dwindle above five or six substrings. This is due to instantiation and destruction overhead for the StringBuilder instance, as well as method-call overhead involved in calling Append() once for every added substring and ToString() once the string is built. What are the alternatives? Plus-sign concatenation and the String.Concat() method are equivalent; I prefer plus signs for readability. Note that this cannot be used across loops because the entire concatenation must occur within a single statement. Example 9 tests String.Concat() vs. StringBuilder for various numbers of substrings.
Don't Be Afraid to Use String Literals
Many developers incorrectly assume that a new object is created for every string literal, and, therefore, avoid their use. In some cases, using string literals directly in your code is a better approach than using string constants! It can make the code easier to understand and has no adverse impact on performance. This is due to the use of the .NET interned string table; this table maintains a String instance for every known string and reuses this instance whenever the same character sequence is used as a literal. See the documentation of the String.Intern() method for more details. Example 10 compares string literals to the use of string constants.
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