单行注释延续
Single line comment continuation
来自 C++ 标准（至少回到 C++98）§ 2.2，注释 2 状态：
Each instance of a backslash character (\) immediately followed by a new-line character is deleted, splicing physical source lines to form logical source lines. Only the last backslash on any physical source line shall be eligible for being part of such a splice. Except for splices reverted in a raw string literal, if a splice results in a character sequence that matches the syntax of a universal-character-name, the behavior is undefined. A source file that is not empty and that does not end in a new-line character, or that ends in a new-line character immediately preceded by a backslash character before any such splicing takes place, shall be processed as if an additional new-line character were appended to the file.
并且，第 2.7 节指出：
The characters /* start a comment, which terminates with the characters */. These comments do not nest. The characters // start a comment, which terminates with the next new-line character. If there is a form-feed or a vertical-tab character in such a comment, only white-space characters shall appear between it and the new-line that terminates the comment; no diagnostic is required. [Note: The comment characters //, /*, and */ have no special meaning within a // comment and are treated just like other characters. Similarly, the comment characters // and /* have no special meaning within a /* comment. ]
我将这两个放在一起表示以下内容：
// My comment \
is valid
// My comment \ still valid \
is valid
在 C++98 中是合法的。在 GCC 4.9.2 中，这些都在没有任何诊断消息的情况下编译。在 MSVC 2013 中，它们都会产生以下内容：
warning C4010: single-line comment contains line-continuation character
如果您启用了警告作为错误（我这样做了），这将导致程序无法成功编译（没有警告作为错误，它工作得很好）。标准中是否有不允许单行注释延续的内容，或者这是 MSVC 不符合标准的情况？
这不是合规问题。您已明确要求编译器将有效构造视为错误，这就是它的作用。
如果您指定 -Wcomment 或 -Wall.
，GCC 将给出相同的警告（或错误，如果需要）
我会说 MS 对以下事实很敏感：
#define macro() \
some stuff \
// Intended as comment \
more stuff
然后在代码中使用 macro() 时会出现非常有趣的错误。
或者其他只是不小心输入了这样的评论：
// The files for foo-project are in c:\projects\foo\
int blah;
（出现 "undefined variable blah" 的奇怪错误）
我绝不会在单行注释中使用续行，但如果您有充分的理由，只需在 MSVC 中关闭该警告即可。
也正如 Mike 所说：标准甚至没有涵盖警告 - 它只说明需要成为错误的内容。如果启用 "warnings are errors"，您将不得不选择启用哪些警告，或者接受某些技术上有效（但可疑）的构造在构建中将不被接受，因为编译器制造商已决定发出警告关于它。尝试在 gcc 或 clang 中编写 if (c = getchar())，看看在 "high" 上有多少 -Werror 和警告。然而，根据标准，它是完全有效的。
来自 C++ 标准（至少回到 C++98）§ 2.2，注释 2 状态：
Each instance of a backslash character (\) immediately followed by a new-line character is deleted, splicing physical source lines to form logical source lines. Only the last backslash on any physical source line shall be eligible for being part of such a splice. Except for splices reverted in a raw string literal, if a splice results in a character sequence that matches the syntax of a universal-character-name, the behavior is undefined. A source file that is not empty and that does not end in a new-line character, or that ends in a new-line character immediately preceded by a backslash character before any such splicing takes place, shall be processed as if an additional new-line character were appended to the file.
并且，第 2.7 节指出：
The characters /* start a comment, which terminates with the characters */. These comments do not nest. The characters // start a comment, which terminates with the next new-line character. If there is a form-feed or a vertical-tab character in such a comment, only white-space characters shall appear between it and the new-line that terminates the comment; no diagnostic is required. [Note: The comment characters //, /*, and */ have no special meaning within a // comment and are treated just like other characters. Similarly, the comment characters // and /* have no special meaning within a /* comment. ]
我将这两个放在一起表示以下内容：
// My comment \
is valid
// My comment \ still valid \
is valid
在 C++98 中是合法的。在 GCC 4.9.2 中，这些都在没有任何诊断消息的情况下编译。在 MSVC 2013 中，它们都会产生以下内容：
warning C4010: single-line comment contains line-continuation character
如果您启用了警告作为错误（我这样做了），这将导致程序无法成功编译（没有警告作为错误，它工作得很好）。标准中是否有不允许单行注释延续的内容，或者这是 MSVC 不符合标准的情况？
这不是合规问题。您已明确要求编译器将有效构造视为错误，这就是它的作用。
如果您指定 -Wcomment 或 -Wall.
我会说 MS 对以下事实很敏感：
#define macro() \
some stuff \
// Intended as comment \
more stuff
然后在代码中使用 macro() 时会出现非常有趣的错误。
或者其他只是不小心输入了这样的评论：
// The files for foo-project are in c:\projects\foo\
int blah;
（出现 "undefined variable blah" 的奇怪错误）
我绝不会在单行注释中使用续行，但如果您有充分的理由，只需在 MSVC 中关闭该警告即可。
也正如 Mike 所说：标准甚至没有涵盖警告 - 它只说明需要成为错误的内容。如果启用 "warnings are errors"，您将不得不选择启用哪些警告，或者接受某些技术上有效（但可疑）的构造在构建中将不被接受，因为编译器制造商已决定发出警告关于它。尝试在 gcc 或 clang 中编写 if (c = getchar())，看看在 "high" 上有多少 -Werror 和警告。然而，根据标准，它是完全有效的。