隐形字符 -ASCII

有 隐形的字符吗？我在谷歌上搜索过隐形字符，结果得到了许多答案，但我对这些答案并不确定。Stack Overflow 上有人能告诉我更多吗？

我还查看了 Facebook 上的一个个人资料，发现用户的个人资料上没有任何名字？这怎么可能？数据库有问题吗？黑客还是什么？

当我在互联网上搜索时，我发现 200D是一个带有 隐形的字符的 ASCII 值。是真的吗？

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最佳答案

How a character is represented is up to the renderer, but the server may also strip out certain characters before sending the document.

You can also have untitled YouTube videos like https://www.youtube.com/watch?v=dmBvw8uPbrA by using the Unicode character ZERO WIDTH NON-JOINER (U+200C), or ‌ in HTML. The code block below should contain that character:

‌‌
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I just went through the character map to get these. They are all in Calibri.

Number    Name                   HTML Code    Appearance
------    --------------------   ---------    ----------
U+2000    En Quad                       " "
U+2001    Em Quad                       " "
U+2002    En Space                      " "
U+2003    Em Space                      " "
U+2004    Three-Per-Em Space            " "
U+2005    Four-Per-Em Space             " "
U+2006    Six-Per-Em Space              " "
U+2007    Figure Space                  " "
U+2008    Punctuation Space             " "
U+2009    Thin Space                    " "
U+200A    Hair Space                    " "
U+200B    Zero-Width Space       ​      "​"
U+200C    Zero Width Non-Joiner  ‌      "‌"
U+200D    Zero Width Joiner      ‍      "‍"
U+200E    Left-To-Right Mark     ‎      "‎"
U+200F    Right-To-Left Mark     ‏      "‏"
U+202F    Narrow No-Break Space         " "
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There is actually a truly invisible character: U+FEFF. This character is called the Byte Order Mark and is related to the Unicode 8 system. It is a really confusing concept that can be explained HERE The Byte Order Mark or BOM for short is an invisible character that doesn't take up any space. You can copy the character bellow between the > and <.

Here is the character:

> <

How to catch this character in action:

  • Copy the character between the > and <,
  • Write a line of text, then randomly put your caret in the line of text
  • Paste the character in the line.
  • Go to the beginning of the line and press and hold the right arrow key.

You will notice that when your caret gets to the place you pasted the character, it will briefly stop for around half a second. This is becuase the caret is passing over the invisible character. Even though you can't see it doesn't mean it isn't there. The caret still sees that there is a character in that area that you pasted the BOM and will pass through it. Since the BOM is invisble, the caret will look like it has paused for a brief moment. You can past the BOM multiple times in an area and redo the steps above to really show the affect. Good luck!

EDIT: Sadly, Stackoverflow doesn't like the character. Here is an example from w3.org: https://www.w3.org/International/questions/examples/phpbomtest.php

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An invisible Character is ​, or U+200b

​
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Other answers are correct - whether a character is invisible or not depends on what font you use. This seems to be a pretty good list to me of characters that are truly invisible (not even space). It contains some chars that the other lists are missing.

'\u2060', // Word Joiner
'\u2061', // FUNCTION APPLICATION
'\u2062', // INVISIBLE TIMES
'\u2063', // INVISIBLE SEPARATOR
'\u2064', // INVISIBLE PLUS
'\u2066', // LEFT - TO - RIGHT ISOLATE
'\u2067', // RIGHT - TO - LEFT ISOLATE
'\u2068', // FIRST STRONG ISOLATE
'\u2069', // POP DIRECTIONAL ISOLATE
'\u206A', // INHIBIT SYMMETRIC SWAPPING
'\u206B', // ACTIVATE SYMMETRIC SWAPPING
'\u206C', // INHIBIT ARABIC FORM SHAPING
'\u206D', // ACTIVATE ARABIC FORM SHAPING
'\u206E', // NATIONAL DIGIT SHAPES
'\u206F', // NOMINAL DIGIT SHAPES
'\u200B', // Zero-Width Space
'\u200C', // Zero Width Non-Joiner
'\u200D', // Zero Width Joiner
'\u200E', // Left-To-Right Mark
'\u200F', // Right-To-Left Mark
'\u061C', // Arabic Letter Mark
'\uFEFF', // Byte Order Mark
'\u180E', // Mongolian Vowel Separator
'\u00AD'  // soft-hyphen
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The question about invisible characters in Unicode deserves a more thorough explanation.

Short answer - there are lots

Here are 134 invisible characters →­؜᠎​‌‍‎‏‪‫‬‭‮⁠⁡⁢⁣⁤⁧⁦⁨⁩𝅳𝅴𝅵𝅶𝅷𝅸𝅹𝅺󠀁󠀠󠀡󠀢󠀣󠀤󠀥󠀦󠀧󠀨󠀩󠀪󠀫󠀬󠀭󠀮󠀯󠀰󠀱󠀲󠀳󠀴󠀵󠀶󠀷󠀸󠀹󠀺󠀻󠀼󠀽󠀾󠀿󠁀󠁁󠁂󠁃󠁄󠁅󠁆󠁇󠁈󠁉󠁊󠁋󠁌󠁍󠁎󠁏󠁐󠁑󠁒󠁓󠁔󠁕󠁖󠁗󠁘󠁙󠁚󠁛󠁜󠁝󠁞󠁟󠁠󠁡󠁢󠁣󠁤󠁥󠁦󠁧󠁨󠁩󠁪󠁫󠁬󠁭󠁮󠁯󠁰󠁱󠁲󠁳󠁴󠁵󠁶󠁷󠁸󠁹󠁺󠁻󠁼󠁽󠁾󠁿← and here is their escaped ASCII representation: U+00AD U+061C U+180E U+200B U+200C U+200D U+200E U+200F U+202A U+202B U+202C U+202D U+202E U+2060 U+2061 U+2062 U+2063 U+2064 U+2067 U+2066 U+2068 U+2069 U+206A U+206B U+206C U+206D U+206E U+206F U+FEFF U+1D173 U+1D174 U+1D175 U+1D176 U+1D177 U+1D178 U+1D179 U+1D17A U+E0001 U+E0020 U+E0021 U+E0022 U+E0023 U+E0024 U+E0025 U+E0026 U+E0027 U+E0028 U+E0029 U+E002A U+E002B U+E002C U+E002D U+E002E U+E002F U+E0030 U+E0031 U+E0032 U+E0033 U+E0034 U+E0035 U+E0036 U+E0037 U+E0038 U+E0039 U+E003A U+E003B U+E003C U+E003D U+E003E U+E003F U+E0040 U+E0041 U+E0042 U+E0043 U+E0044 U+E0045 U+E0046 U+E0047 U+E0048 U+E0049 U+E004A U+E004B U+E004C U+E004D U+E004E U+E004F U+E0050 U+E0051 U+E0052 U+E0053 U+E0054 U+E0055 U+E0056 U+E0057 U+E0058 U+E0059 U+E005A U+E005B U+E005C U+E005D U+E005E U+E005F U+E0060 U+E0061 U+E0062 U+E0063 U+E0064 U+E0065 U+E0066 U+E0067 U+E0068 U+E0069 U+E006A U+E006B U+E006C U+E006D U+E006E U+E006F U+E0070 U+E0071 U+E0072 U+E0073 U+E0074 U+E0075 U+E0076 U+E0077 U+E0078 U+E0079 U+E007A U+E007B U+E007C U+E007D U+E007E U+E007F

Are there more? Yes.

Are there invisible characters in the ASCII range? Depends on the font.

Long answer - ready? set. go!

The Unicode Standard enables anyone to read and write in their own language. To do that, it lists unique code points󠁗󠁲󠁩󠁴󠁴󠁥󠁮󠀠󠁢󠁹󠀠󠁚󠁶󠁩󠀠󠁁󠁺󠁲󠁡󠁮󠀠󠀻󠀩 (U+hex), that are categorized into letters (D,ž,Dž,ʶ,愛,𓂀), symbols (+∊≠,£¥₪,҂˚˟˿), marks (ם֑֟֯ ,ী,◌҉ ), separators ( , , , ,  ), emojis (😊,🙏,👍), and much more. ASCII/Basic Latin is the very beginning of the table and more code points are added every update.

Simply listing unique numbers for characters is not enough. Characters can change their shape or change the sentence depending on the context. To support that, every code point comes with a list of properties . These properties may define the width (AＡ), its role in the sentence (-“.), its direction (cכ), and much more.

Most invisible characters have the property General_Category=Format (other answers here included Spaces as well). Theis characters have a supporting role to a word/sentence. Here are some examples:

  • General Punctuation Block - Invisible characters that are an integral part of some writing systems and emojis. Common ones are Zero width joiner (U+200D), Zero width non joiner (U+200C), Word joiner (U+2060)
  • Explicit Bidirectional Formatting characters - 12 invisible characters󠁗󠁲󠁩󠁴󠁴󠁥󠁮󠀠󠁢󠁹󠀠󠁚󠁶󠁩󠀠󠁁󠁺󠁲󠁡󠁮󠀠󠀻󠀩 used to enforce different direction constraints on the sentence. Helping present text to more than 300 million speakers of right-to-left languages e.g. Hebrew or Arabic.
  • Tags - 97 invisible characters that mirror ASCII (just drop the E and you get characters in the ASCII range). These are used as emoji modifiers and digital signatures to prove who copied your text.

This all leads to talk about exploiting invisible characters for homograph attack/visual spoofing. Sometimes it's harmless like invisible names and titles but in lots of cases they are used maliciously. For example U+202E is one invisible character that keeps doing more harm than good for decades!!

Last point, there is another way to make invisible characters using fonts. Fonts are files that store glyphs (pictures of characters), that present the characters' look. If the font does not contain a glyph for a codepoint, a substitute/replacement󠁗󠁲󠁩󠁴󠁴󠁥󠁮󠀠󠁢󠁹󠀠󠁚󠁶󠁩󠀠󠁁󠁺󠁲󠁡󠁮󠀠󠀻󠀩 character is displayed (e.g. �, □). But if the font contains a transparent glyph for a codepoint, then the character is invisible, only when displayed by that font. This is the only way to have invisible characters in the ASCII range (for example can you see →``← U+000C Form Feed).

Hope you find this explanation helpful and may you check strings for invisible characters more often 󠁗󠁲󠁩󠁴󠁴󠁥󠁮󠀠󠁢󠁹󠀠󠁚󠁶󠁩󠀠󠁁󠁺󠁲󠁡󠁮󠀠󠀻󠀩😉


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