StringBuilder 真的比连接十几个字符串慢吗? [英] Is it true that StringBuilder is slower than concatenate a dozen of strings?

问题描述

StringBuilder 真的比连接十几个字符串还慢吗?编译器如何优化字符串拼接，使得使用+"连接十几个字符串会比StringBuilder更好?

Is it true that StringBuilder is slower than concatenate a dozen of strings? How does compiler optimize the string concatenation so that joining a dozen of strings using "+" will be better than StringBuilder?

从一本书(由 Ben Watson 撰写)中说:

From a book (written by Ben Watson) it says that:

String Concatenation:用于简单的已知字符串的连接(在编译时time) 字符串的数量，只需使用+"运算符或String.Concat 方法.这通常比使用字符串生成器.字符串结果 = a + b + c + d + e + f；不要考虑 StringBuilder 直到字符串的数量是可变的并且可能大于几十个.编译器将优化简单以减少内存开销的方式进行字符串连接.

String Concatenation: For simple concatenation of a known (at compile time) quantity of strings, just use the ‘+’ operator or the String.Concat method. This is usually more efficient than using a StringBuilder. string result = a + b + c + d + e + f; Do not consider StringBuilder until the number of strings is variable and likely larger than a few dozen. The compiler will optimize simple string concatenation in a way to lessen the memory overhead.

推荐答案

String.Concat 效率更高，因为它从一开始就知道所有字符串长度.因此它可以分配一个长度合适的缓冲区，将字符串复制到其中并返回该缓冲区.

String.Concat is more efficient because it knows all the string lengths from the start. So it can allocate a single buffer with just the right length, copy the strings into it and return that buffer.

StringBuilder 必须分配一个小缓冲区，每次调用 Append 时都会重新分配和复制导致空间不足.对 ToString() 的最后调用还必须分配另一个缓冲区.

StringBuilder has to allocate a small buffer, reallocating and copying everytime a call to Append causes it to run out of space. The final call to ToString() also has to allocate yet another buffer.

所以当你事先知道你有多少个字符串时，使用String.Concat；不使用时使用 StringBuilder.

So use String.Concat when you know in advance how many strings you have; use StringBuilder when you don't.

在 C# 中，对 + 运算符的链式调用会自动转换为对 String.Concat 的单个调用.

In C#, chained calls to the + operator are automatically converted to a single call to String.Concat.

这篇关于StringBuilder 真的比连接十几个字符串慢吗?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！