Pedantic：什么是源文件？什么是头？ [英] Pedantic: What Is A Source File? What Is A Header?

问题描述

对于这个问题，我只感兴趣的是符合标准的C ++，而不是C或C ++ 0x，而不是任何实现的具体细节。

问题不时出现关于 #include和 #include<> 之间的差异。该参数通常归结为两个区别：

1. 特定实现通常搜索两种形式的不同路径。这是平台特定的，不在此问题的范围内。


2. 标准说 #include<> headers， #include用于源文件。这是相关的参考：

ISO / IEC 14882： h1>

16.2源文件包含[cpp.include]

include指令应标识可由实现处理的头文件或源文件。

2
<$ p $形式的预处理指令p> ＃include< h-char-sequence>新行

搜索一系列实现定义的地方， ><<<<<<>标识符之间唯一地标识的头部，并且使得该指令被头部的全部内容替换。

3 格式为

 的预处理指令code>＃includeq-char-sequencenew-line  

会导致该指令被源文件，由指定的序列在分隔符之间进行识别。以实现定义的方式搜索指定的源文件。如果不支持此搜索，或者搜索失败，则重新处理指令，读取

 ＃include< h-char-sequence>新行 

（上面引用的重点是我的）。这个差异似乎是标准打算区分头文件和源文件，但文档没有定义这些术语或它们之间的差异。

很少有其他地方甚至提到头文件或源文件。一些：

158）头部不一定是源文件，头部名称中定义的序列也不一定是有效的源文件名（16.2）。

似乎意味着头文件可能不驻留在文件系统中，但它不会说源文件。

< blockquote>

2词汇约定[lex]

1 程序的文本保存在称为源文件本国际标准。通过预处理指令 #include ，源文件与所有标题（17.4.1.2）和源文件（16.2）一起，减少任何条件包含（16.1）预处理指令，被称为翻译单元。 [注：一个C ++程序不需要全部同时翻译。 ]

这是我可以找到的最接近的定义，它似乎暗示标题不是程序的文本。但是如果你 #include 一个头，它不会成为程序的文本的一部分？这是有点误导。

那么什么是标题？什么是源文件？

解决方案

这不是说标题可以实现为源文件，未必？对于什么是源文件，似乎非常明智的标准没有拼写出来，因为文件的许多方式实现。

For the purposes of this question, I am interested only in Standard-Compliant C++, not C or C++0x, and not any implementation-specific details.

Questions arise from time to time regarding the difference between #include "" and #include <>. The argument typically boils down to two differences:

1. Specific implementations often search different paths for the two forms. This is platform-specific, and not in the scope of this question.
2. The Standard says #include <> is for "headers" whereas #include "" is for a "source file." Here is the relevant reference:

ISO/IEC 14882:2003(E)

16.2 Source file inclusion [cpp.include]

1 A #include directive shall identify a header or source file that can be processed by the implementation.

2 A preprocessing directive of the form

# include  < h-char-sequence > new-line

searches a sequence of implementation-defined places for a header identified uniquely by the specified sequence between the < and > delimiters, and causes the replacement of that directive by the entire contents of the header. How the places are specified or the header identified is implementation-defined.

3 A preprocessing directive of the form

# include "q-char-sequence" new-line

causes the replacement of that directive by the entire contents of the source file identified by the specified sequence between the " delimiters. The named source file is searched for in an implementation-defined manner. If this search is not supported, or if the search fails, the directive is reprocessed as if it read

# include  < h-char-sequence > new-line

with the identical contained sequence (including > characters, if any) from the original directive.

(Emphasis in quote above is mine.) The implication of this difference seems to be that the Standard intends to differentiate between a 'header' and a 'source file', but nowhere does the document define either of these terms or the difference between them.

There are few other places where headers or source files are even mentioned. A few:

158) A header is not necessarily a source file, nor are the sequences delimited by in header names necessarily valid source file names (16.2).

Seems to imply a header may not reside in the filesystem, but it doesn't say that source files do, either.

2 Lexical conventions [lex]

1 The text of the program is kept in units called source files in this International Standard. A source file together with all the headers (17.4.1.2) and source files included (16.2) via the preprocessing directive #include, less any source lines skipped by any of the conditional inclusion (16.1) preprocessing directives, is called a translation unit. [Note: a C + + program need not all be translated at the same time. ]

This is the closest I could find to a definition, and it seems to imply that headers are not the "text of the program." But if you #include a header, doesn't it become part of the text of the program? This is a bit misleading.

So what is a header? What is a source file?

解决方案

Isn't this saying that a header may be implemented as a source file, but there again may not be? as for "what is a source file", it seems very sensible for the standard not to spell this out, given the many ways that "files" are implemented.

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