A header file is a file with extension . C function declarations and macro definitions to be shared between several source files. There are two types of header files: the files that the programmer HEADER FILES and the files that comes with your compiler.
This form is used for system header files. It searches for a file named ‘file’ in a standard list of system directories. You can prepend directories to this list with the -I option while compiling your source code. This form is used for header files of your own program. It searches for a file named ‘file’ in the directory containing the current file. C preprocessor to scan the specified file as input before continuing with the rest of the current source file. For example, if you have a header file header.
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When the header is included again, the conditional will be false, because HEADER_FILE is defined. The preprocessor will skip over the entire contents of the file, and the compiler will not see it twice. Computed Includes Sometimes it is necessary to select one of the several different header files to be included into your program. For instance, they might specify configuration parameters to be used on different sorts of operating systems. But as it grows, it becomes tedious, instead the preprocessor offers the ability to use a macro for the header name. This is called a computed include.
SYSTEM_H could be defined by your Makefile with a -D option. Readable and portable Markdown style guide. This project is community driven, and tries to reach consensus. Maintainers will only step in if the community cannot reach a decision. Discussion will take place on the issue tracker.
Do you use this style guide? Add your name to our wiki. Please inform this on the pull request that adds you to the notable list. Markdown engines, text editors, lots of markdown documentation, etc.
Any popularity measure will be taken into account, e. Options system Disputed points will be given multiple alternative style options. Each feature and option will receive a lowercase hyphen separated identifier. The first option header that appears in this text is the default value. Portability tests are carried out with the Markdown Test Suite.
Editor features like syntax highlighting and line wrapping can greatly reduce problems, but it is of course better if people don’t need to change their editors at all. Stack Overflow, people will very rarely read the source, only the rendered output. So it might be better to optimize writing speed. The current style is inconsistent with either of those optimizations. Typographic conventions When this style guide needs to represent multiple adjacent spaces, or spaces at the beginning or ending of code blocks, this will be mentioned explicitly in prose, and a dot will be used to make the space visible. This guide was originally forked from it. It has been extended considerably, some decisions were modified, and no original lines remain.
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General rules File File extension Use . Rationale: why not underscore or camel case? HTML files in the same project, possibly the same directory as the markdown files. Whitespaces Newlines Don’t use 2 or more consecutive empty lines, that is, more than two consecutive newline characters, except where they must appear literally such as in code blocks. End files with a newline character, and don’t leave empty lines at the end of the file. Don’t use trailing whitespace unless it has a function such as indicating a line break.
Rationale: multiple empty lines occupy more vertical screen space, and do not significantly improve readability. Spaces after sentences Option space-sentence:1 Use a single space after sentences. It is acceptable to have a line longer than 80 characters, but keep in mind that long sentences are less readable and look worse in tools such as git diff. Set your editor to wrap lines visually for Markdown in case a large line is present. This is a very very very very very very very very very very very very very long not wrapped sentence. Second sentence of of the paragraph, third sentence of a paragraph and the fourth one. Diffs look better, since a change to a clause shows up as a single diff line.
Occasional visual wrapping does not significantly reduce the readability of Markdown, since the only language feature that can be indented to indicate hierarchy are nested lists. Currently there is no major engine which does it, so it is safe to use newlines. Some tools are not well adapted for long lines, e. Vim and git diff will not wrap lines by default. This can be configured however via git config –global core.
Git and set wrap for Vim. Markdown does not look like the rendered output, in which there are no line breaks. Manual line breaking can make the Markdown more readable than the rendered output, which is bad because it gives a false sense of readability encouraging less readable long paragraphs. Requires users of programming text editors like Vim, which are usually configured to not wrap, to toggle visual wrapping on. But diffs on huge lines are hard to read.
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Option wrap:space Always wrap at the end of the first word that exceeds 80 characters. Rationale: source code becomes is very readable and text editors support it automatically. But diffs will look bad, and changing lines will be hard. Option wrap:sentence Rationale: similar advantages as wrap:inner-sentence, but easier for people to follow since the rule is simple: break after the period. But may produce long lines with hard to read diffs.
If the goal is to clarify what the language is, do it on the preceding paragraph. Rationale: harder to copy paste, noisier to read. Differentiate between tool and the name of related projects. Spelling and grammar Use correct spelling and grammar.
Prefer writing in English, and in particular American English. Rationale: American English speakers have the largest GDP, specially in the computing industry. Use markup like URL or code on words which you do not want to add to your dictionary so that spell checkers can ignore them automatically. When in doubt, prefer the same abbreviation as used on Wikipedia. Block elements Line breaks Avoid line breaks, as they don’t have generally accepted semantic meaning. In the rare case you absolutely need them, end a lines with exactly two spaces. Not very important if you have syntax highlighting.
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Surround headers by a single empty line except at the beginning of the file. Avoid using two headers with the same content in the same markdown file. Rationale: many markdown engines generate IDs for headers based on the header content. Top-level header If you target HTML output, write your documents so that it will have one and only one h1 element as the first thing in it that serves as the title of the document.
This is the HTML top-level header. How this h1 is produced may vary depending on your exact technology stack: some stacks may generate it from metadata, for example Jekyll through the front-matter. Storing the top-level header as metadata has the advantage that it can be reused elsewhere more easily, e. If your target stack does not generate the top-level header in another way, include it in your markdown file. Top-level headers on index-like files such as README. In most cases, the filename can be trivially converted to a top-level, e.
URL’s, especially for non-technically inclined users. The other letters have the same case they would have in the middle of a sentence. As an exception, title case may be optionally used for the top-level header. Use this exception sparingly, in cases where typographical perfection is important, e.
Rationale: why not Title case for all headers? It requires too much effort to decide if edge-case words should be upper case or not. Header length Keep headers as short as possible. Instead of using a huge sentence, make the header a summary to the huge sentence, and write the huge sentence as the first paragraph beneath the header.
Rationale: it is easier to refer to the header later, specially if automatic IDs or a TOC are generated by the implementation. Huge header Huge header that talks about a complex subject. Punctuation at the end of headers Don’t add a trailing colon : to headers. Rationale: every header is an introduction to what is about to come next, which is exactly the function of the colon. Don’t add a trailing period . Rationale: every header consists of a single short sentence, so there is not need to add a sentence separator to it. Header synonyms Headers serve as an index for users searching for keywords.
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For this reason, you may want to give multiple keyword possibilities for a given header. To do so, simply create a synonym header with empty content just before its main header. Buy You give money and get something in return. Every empty header with the same level as the following one is assumed to be a synonym.
Use a greater than sign for every line, including wrapped. Don’t use empty lines inside a single block quote. Lists Marker Unordered Option list-marker:hyphen Use the hyphen marker. Ordered Prefer lists only with the marker 1.
Prefer unordered lists unless you intent to refer to items by their number. The ouput of the `ls` command is of the form: drwx—— 2 ciro ciro 4096 Jul 5 2013 dir0 drwx—— 4 ciro ciro 4096 Apr 27 08:00 dir1 1 2 Where: 1. I will not do anything illegal. I will not do anything that can harm the website. If you want to change a list item in the middle of the list, you don’t have to modify all items that follow it. Diffs will show only the significant line which was modified. Content stays aligned without extra effort if the numbers reach 2 digits.
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References break when a new list item is added. One less than for unordered because the marker is 2 chars long. Option list-space:1 Always add one space to the list marker. You never need to change the indentation of the entire list because of a new item. Note how a and b were changed because of c. That means that you cannot easily configure your editor indent level to deal with all cases when you want to change the indentation level of multiple list item lines. Is not implemented consistently across editors.
Indentation of content inside lists The indentation level of what comes inside list and of further list items must be the same as the first list item. Avoid starting a list item directly with indented code blocks because that is not consistently implemented. Empty lines inside lists If every item of a list is a single line long, don’t add empty lines between items. Otherwise, add empty lines between every item.
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Rationale: it is hard to tell where multi-line list items start and end without empty lines. Empty lines around lists Surround lists by one empty line. Case of first letter of list item Each list item has the same case as it would have if it were concatenated with the sentence that comes before the list. To ride a bike you have to: – get on top of the bike. This is the most fun part.
To ride a bike you have to get on top of the bike. To ride a bike you have to put your foot on the pedal. To ride a bike you have to push the pedal. How to ride a bike – Get on top of the bike.
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Put your feet on the pedal. How to ride a bike Get on top of the bike. Otherwise, omit the punctuation if it would be a period. Good, not terminated by period but by other punctuation. Bad for wallet – finally eat the fruit.
Note: nothing forbids one list item from ending in period while another in the same list does not. Code blocks Option code:fenced Only use fenced code blocks. Always specify the language of the code is applicable. Option code:indented Only use indented code blocks. Indent indented code blocks with 4 spaces. Code blocks must be surrounded by one empty line. Prefer to end the phrase before a code block with a colon :.
Horizontal rules Don’t use horizontal rules except to indicate the End of a header. Surround tables by one empty line. Surround every line of the table by pipes. Column width is determined by the longest cell in the column. Trailing pipes make it look better because of symmetry. Downside: harder to implement automatic alignment in editors, as it requires a special rule for the separator line.
Span elements Don’t use inner spaces. Use the hyphen marker followed by one space `- a` for unordered lists. Single or double quote titles Use double quotes, not single quotes. Rationale: single quotes do not work in all major implementations, double quotes do.