tmp/tmpxmcqamjp/{from.md → to.md}
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| 1 |
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#### Formatting escaped characters and strings <a id="format.string.escaped">[[format.string.escaped]]</a>
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A character or string can be formatted as *escaped* to make it more
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suitable for debugging or for logging.
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The escaped string *E* representation of a string *S* is constructed by
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encoding a sequence of characters as follows. The associated character
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encoding *CE* for `charT` ([[lex.string.literal]]) is used to both
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interpret *S* and construct *E*.
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- U+0022 (quotation mark) (`"`) is appended to *E*.
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- For each code unit sequence *X* in *S* that either encodes a single
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character, is a shift sequence, or is a sequence of ill-formed code
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units, processing is in order as follows:
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- If *X* encodes a single character *C*, then:
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- If *C* is one of the characters in [[format.escape.sequences]],
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then the two characters shown as the corresponding escape sequence
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are appended to *E*.
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- Otherwise, if *C* is not U+0020 (space) and
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- *CE* is UTF-8, UTF-16, or UTF-32 and *C* corresponds to a
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Unicode scalar value whose Unicode property `General_Category`
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has a value in the groups `Separator` (`Z`) or `Other` (`C`), as
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described by UAX \#44 of the Unicode Standard, or
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- *CE* is UTF-8, UTF-16, or UTF-32 and *C* corresponds to a
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Unicode scalar value with the Unicode property
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`Grapheme_Extend=Yes` as described by UAX \#44 of the Unicode
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Standard and *C* is not immediately preceded in *S* by a
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character *P* appended to *E* without translation to an escape
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sequence, or
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- *CE* is neither UTF-8, UTF-16, nor UTF-32 and *C* is one of an
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implementation-defined set of separator or non-printable
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characters
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then the sequence `\u{hex-digit-sequence}` is appended to *E*,
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where `hex-digit-sequence` is the shortest hexadecimal
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representation of *C* using lower-case hexadecimal digits.
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- Otherwise, *C* is appended to *E*.
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- Otherwise, if *X* is a shift sequence, the effect on *E* and further
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decoding of *S* is unspecified. *Recommended practice:* A shift
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sequence should be represented in *E* such that the original code
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unit sequence of *S* can be reconstructed.
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- Otherwise (*X* is a sequence of ill-formed code units), each code
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unit *U* is appended to *E* in order as the sequence
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`\x{hex-digit-sequence}`, where `hex-digit-sequence` is the shortest
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hexadecimal representation of *U* using lower-case hexadecimal
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digits.
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- Finally, U+0022 (quotation mark) (`"`) is appended to *E*.
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**Table: Mapping of characters to escape sequences** <a id="format.escape.sequences">[format.escape.sequences]</a>
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| Character | Escape sequence |
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| ----------------------------- | --------------- |
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| U+0009 (character tabulation) | `\t` |
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| % U+000a (line feed) | `\n` |
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| % U+000d (carriage return) | `\r` |
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| % U+0022 (quotation mark) | `\"` |
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| % U+005c (reverse solidus) | `` |
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The escaped string representation of a character *C* is equivalent to
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the escaped string representation of a string of *C*, except that:
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- the result starts and ends with U+0027 (apostrophe) (`'`) instead of
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U+0022 (quotation mark) (`"`), and
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- if *C* is U+0027 (apostrophe), the two characters `\'` are appended to
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*E*, and
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- if *C* is U+0022 (quotation mark), then *C* is appended unchanged.
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[*Example 1*:
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``` cpp
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string s0 = format("[{}]", "h\tllo"); // s0 has value: [h\ \ \ \ llo]
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string s1 = format("[{:?}]", "h\tllo"); // s1 has value: ["h\ tllo"]
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string s3 = format("[{:?}, {:?}]", '\'', '"'); // s3 has value: ['\ '', '"']
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// The following examples assume use of the UTF-8 encoding
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string s4 = format("[{:?}]", string("\0 \n \t \x02 \x1b", 9));
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// s4 has value: ["\ u{0\ \ n \ t \ u{2} \ u{1b}"]}
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string s5 = format("[{:?}]", "\xc3\x28"); // invalid UTF-8, s5 has value: ["\ x{c3\("]}
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string s7 = format("[{:?}]", "\u0301"); // s7 has value: ["\ u{301"]}
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string s8 = format("[{:?}]", "\\\u0301"); // s8 has value: ["\ \ \ u{301"]}
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```
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— *end example*]
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