Lua string Library (string library) learning notes _lua

One of the most powerful features of Lua is its string processing power, it supports character formatted output, extensible pattern matching lookup, and some useful character manipulations, such as query, intercept, replace, and delete string operations, which are encapsulated in a module named String.

The character index in Lua starts at 1 and the index value can be negative, which is interpreted as a backward index, starting at the end of the string.

Here is the string manipulation function provided by Lua 5.2:

Byte

The function string.byte the first character of the string into ASCII encoding by default, which is the encoding (with only one argument) for the output of the character:

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String.byte (s [, I [, J]])

Example:

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Print (String.byte ("abc"))//echo:97

Print (String.byte ("abc", 2)//echo:98

Char

function String.char is to convert an ASCII encoding to the corresponding character, using:

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String.char (ASC1, ...)

Example:

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Print (String.char)//echo A

Print (String.char,)//echo CDE

Dump

function String.dump Returns a string of functions in binary form, using:

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String.dump (function)

The parameter function is a Lua function:

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function test ()
Print ("Just a Test")
End
Print (String.dump (test))

function String.dump implements serialization of functions, which can be easily passed and invoked in other scopes. function string.dump the binary string, which can be returned directly by the load function inverse sequence.

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function test ()
Print ("Just a Test")
End
Local SD = string.dump (test)
Print (SD)
Local ls = load (SD)
Print (LS)
LS ()

Find

Function String.find Find the first position in the string s that matches the find character pattern:

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String.find (s, pattern [, init [, plain]])

If the target character pattern is found, its start and end positions are returned:

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Start, end = String.find ("Just a Test", "St")
Print (start, end)

If not found, returns nil:

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Print (String.find ("Just a Test", "dhq.me"))

Format

Function String.Format is used to format strings for output, using:

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String.Format (formatstring,)

The first parameter of the String.Format function is used to specify the format of the string, for example:

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Print (String.Format ("%s is%d", "ten", 10))

The%s in the example above represents a string, and%d represents a number, which is a formatted output symbol for LUA.

The use of the String.Format function is similar to the printf function in C, for example, it can output a specified number of digits like printf:

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Pi = 3.1415926
Print (String.Format ("Pi is%.2f", pi))

Lua's character formatted output symbol list:

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. All characters
%a Letters
%c control character
%d digits
%d Non-numeric
%l lowercase Letters
%p Punctuation Mark
%s string
%u uppercase letters
%w Alpha-Numeric
%x Hex Number
%z characters in 0

Gmatch

The function String.gmatch returns an iterative function that Karki through the function to all occurrences of a string s that appear in the specified pattern of matching patterns:

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String.gmatch (s, pattern)

For example, find all the words in the string s:

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s = "Just a test"
For W in String.gmatch (S, "%a+") does
Print (W)
End

Gsub

The function string.gsub is used for global string substitution, and characters in the string s that match pattern patterns are replaced with the values of the REPL parameter, using:

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String.gsub (s, pattern, repl [, N])

For example:

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Print (String.gsub ("Just a Test", "St", "*"))

Matching pattern patterns can be a regular:

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s = "num is 1234567890"
Print (String.gsub (S, "%d", "*"))

You can add an optional argument n to the end of the function to specify the number of times to replace it:

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s = "Sethook, setlocal, setmetatable, Setupvalue, Setuservalue"
Print (String.gsub (S, "s%a+", "s", 2))

Len

function String.len is used to return the length of the string s, using:

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String.len (s)

Example:

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Print (String.len ("ABCDEFG"))

Lower

The function string.lower is used to convert the letters in the string s to lowercase, using:

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String.Lower (s)

For example:

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Print (String.Lower ("AbCdEfG"))

Match

The function String.match is used to find the first matching value of pattern patterns in the string s, and returns a matching value, using:

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String.match (s, pattern [, Init])

The above parameter init is optional, representing the starting point for the lookup process, which begins with 1:

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Print (String.match ("Just a Test", "test")

The parameter patter can be a regular pattern:

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T = "Today is 2003-5-31"
Print (String.match (t, "%d+-%d+-%d+"))

Returns the entire string if pattern is empty, or returns nil if the match is not successful.

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Print (String.match ("Abcdabcd", "a"))

Rep

function String.rep Returns a string of duplicate (repeat) n-second character s, separated by the separator sep, using:

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String.rep (S, n [, Sep])

The default delimiter Sep is a null character.

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Print (String.rep ("Repeat", 3))

Reverse

function String.reverse is used to reverse the ordering of a string s, using:

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String.reverse (s)

For example:

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Print (String.reverse ("reverse"))

Sub

function string.sub is used to intercept a substring from the first and the J characters from the string s, using:

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String.sub (S, I [, j])

For example:

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Print (String.sub ("ABCDEFG", 2, 5))

Parameter I can be a negative number, in which case the position of the substring begins at the end of the string s:

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Print (String.sub ("ABCDEFG",-4,-2))

Argument end is omitted, a substring from I to the bottom of the string is returned:

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Print (String.sub ("ABCDEFG", 3))

Upper

The function string.upper is used to capitalize the letters in the string s, using:

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String.upper (s)

For example:

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Print (String.upper ("AbCdEfG"))