c# - ADO 命令文本语法

Question

有谁知道为什么有时在 commandText 字符串之前使用 @？

两者似乎都工作正常。

command.CommandText = @"SELECT id FROM users";

或

command.CommandText = "SELECT id FROM users";

Answer 1

这是 C# 的逐字字符串文字表示法。

逐字字符串文字前面有一个前导 @ 以及 @ 之后的引号之间的任何内容将被视为字符串文字的一部分，无需转义。

请参阅String literals :

C# supports two forms of string literals: regular string literals and verbatim string literals.

A regular string literal consists of zero or more characters enclosed in double quotes, as in "hello", and may include both simple escape sequences (such as \t for the tab character) and hexadecimal and Unicode escape sequences.

A verbatim string literal consists of an @ character followed by a double-quote character, zero or more characters, and a closing double-quote character. A simple example is @"hello". In a verbatim string literal, the characters between the delimiters are interpreted verbatim, the only exception being a quote-escape-sequence. In particular, simple escape sequences and hexadecimal and Unicode escape sequences are not processed in verbatim string literals. A verbatim string literal may span multiple lines.

很可能一个查询跨越多行，编写代码的人都想像这样把它放在多行上:

command.CommandText = @"SELECT id
                       FROM users";

如果没有逐字字符串文字，您将不得不这样做:

command.CommandText = "SELECT id"
                      + " FROM users";