String functions are used in computer programming languages to manipulate a string or query information about a string (some do both).

Most programming languages that have a string datatype will have some string functions although there may be other low-level ways within each language to handle strings directly. In object-oriented languages, string functions are often implemented as properties and methods of string objects. In functional and list-based languages a string is represented as a list (of character codes), therefore all list-manipulation procedures could be considered string functions. However such languages may implement a subset of explicit string-specific functions as well.

For function that manipulate strings, modern object-oriented languages, like C# and Java have immutable strings and return a copy (in newly allocated dynamic memory), while others, like C manipulate the original string unless the programmer copies data to a new string. See for example Concatenation below.

The most basic example of a string function is the length(string) function. This function returns the length of a string literal.

e.g. length("hello world") would return 11.

Other languages may have string functions with similar or exactly the same syntax or parameters or outcomes. For example in many languages the length function is usually represented as len(string). The below list of common functions aims to help limit this confusion.

Common string functions (multi language reference)

String functions common to many languages are listed below, including the different names used. The below list of common functions aims to help programmers find the equivalent function in a language. Note, string concatenation and regular expressions are handled in separate pages. Statements in guillemets (« … ») are optional.

CharAt

{ Example in Pascal }
var 
  MyStr: string = 'Hello, World';
  MyChar: Char;
begin
  MyChar := MyStr[2];         // 'e'

# Example in ALGOL 68 #
"Hello, World"[2];         // 'e'

// Example in C# and Ya
"Hello, World"[2];         // 'l'

# Examples in Python
"Hello, World"[2]          #  'l'
"Hello, World"[-3]         #  'r'

' Example in Visual Basic
Mid("Hello, World",2,1)

' Example in Visual Basic .NET
"Hello, World".Chars(2)    '  "l"c

" Example in Smalltalk "
'Hello, World' at: 2.    "$e"

Compare (integer result)

# Example in Python
cmp("hello", "world")      # returns -1

/** Example in REXX */ 
compare("hello", "world")  /* returns index of mismatch: 1 */

; Example in Scheme
(use-modules (srfi srfi-13))
; returns index of mismatch: 0
(string-compare "hello" "world" values values values)

Compare (relational operator-based, Boolean result)

% Example in Erlang
"hello" > "world".            % returns false

# Example in Windows PowerShell
"hello" -gt "world"           # returns false

;; Example in Common Lisp
(string> "art" "painting")      ; returns nil
(string< "art" "painting")      ; returns non nil

Concatenation

{ Example in Pascal }
'abc' + 'def';      // returns "abcdef"

// Example in C#
"abc" + "def";      // returns "abcdef"

' Example in Visual Basic
"abc" & "def"       '  returns "abcdef"
"abc" + "def"       '  returns "abcdef"
"abc" & Null        '  returns "abc"
"abc" + Null        '  returns Null

// Example in D
"abc" ~ "def";      // returns "abcdef"

;; Example in common lisp
(concatenate 'string "abc " "def " "ghi")  ; returns "abc def ghi"

Contains

¢ Example in ALGOL 68 ¢
string in string("e", loc int, "Hello mate");      ¢ returns true ¢
string in string("z", loc int, "word");            ¢ returns false ¢

// Example In C#
"Hello mate".Contains("e");      // returns true
"word".Contains("z");            // returns false

#  Example in Python
"e" in "Hello mate"              #  returns true
"z" in "word"                    #  returns false

"  Example in Smalltalk "
'Hello mate' includesSubstring: 'e'  " returns true "
'word' includesSubstring: 'z'        " returns false "

Equality

Tests if two strings are equal. See also #Compare and #Compare. Note that doing equality checks via a generic Compare with integer result is not only confusing for the programmer but is often a significantly more expensive operation; this is especially true when using "C-strings".

// Example in C#
"hello" == "world"           // returns false

' Example in Visual Basic
"hello" = "world"            '  returns false

# Example in Windows PowerShell
"hello" -eq "world"          #  returns false

Find

; Examples in Common Lisp
(search "e" "Hello mate")             ;  returns 1
(search "z" "word")                   ;  returns NIL

// Examples in C#
"Hello mate".IndexOf("e");            // returns 1
"Hello mate".IndexOf("e", 4);         // returns 9
"word".IndexOf("z");                  // returns -1

; Examples in Scheme
(use-modules (srfi srfi-13))
(string-contains "Hello mate" "e")    ;  returns 1
(string-contains "word" "z")          ;  returns #f

' Examples in Visual Basic
InStr("Hello mate", "e")              '  returns 2
InStr(5, "Hello mate", "e")           '  returns 10
InStr("word", "z")                    '  returns 0

" Examples in Smalltalk "
'Hello mate' indexOfSubCollection:'ate'  "returns 8"
'Hello mate' indexOfSubCollection:'late' "returns 0"
I'Hello mate' 
    indexOfSubCollection:'late'
    ifAbsent:[ 99 ]                      "returns 99"
'Hello mate' 
    indexOfSubCollection:'late'
    ifAbsent:[ self error ]              "raises an exception"

Find character

// Examples in C#
"Hello mate".IndexOf('e');              // returns 1
"word".IndexOf('z')                     // returns -1

; Examples in Common Lisp
(position #\e "Hello mate")             ;  returns 1
(position #\z "word")                   ;  returns NIL

^a Given a set of characters, SCAN returns the position of the first character found,^[10] while VERIFY returns the position of the first character that does not belong to the set.^[11]

Format

// Example in C#
String.Format("My {0} costs {1:C2}", "pen", 19.99); // returns "My pen costs $19.99"

// Example in Object Pascal (Delphi)
Format('My %s costs $%2f', ['pen', 19.99]);         // returns "My pen costs $19.99"

// Example in Java
String.format("My %s costs $%2f", "pen", 19.99);    // returns "My pen costs $19.99"

# Example in Python
"My %s costs $%.2f" % ("pen", 19.99);                #  returns "My pen costs $19.99"
"My {0} costs ${1:.2f}".format("pen", 19.99);        #  returns "My pen costs $19.99"

; Example in Scheme
(format "My ~a costs $~1,2F" "pen" 19.99)           ;  returns "My pen costs $19.99"

/* example in PL/I */
put string(some_string) edit('My ', 'pen', ' costs', 19.99)(a,a,a,p'$$$V.99')
/* returns "My pen costs $19.99" */

Inequality

Tests if two strings are not equal. See also #Equality.

// Example in C#
"hello" != "world"    // returns true

' Example in Visual Basic
"hello" <> "world"    '  returns true

;; Example in Clojure
(not= "hello" "world")  ; ⇒ true

# Example in Windows PowerShell
"hello" -ne "world"   #  returns true

index

see #Find

indexof

see #Find

instr

see #Find

instrrev

see #rfind

join

// Example in C#
String.Join("-", {"a", "b", "c"})  // "a-b-c"

" Example in Smalltalk "
#('a' 'b' 'c') joinUsing: '-'      " 'a-b-c' "

# Example in Perl
join( '-', ('a', 'b', 'c'));       # 'a-b-c'

# Example in Python
"-".join(["a", "b", "c"])          #  'a-b-c'

# Example in Ruby
["a", "b", "c"].join("-")          #  'a-b-c'

; Example in Scheme
(use-modules (srfi srfi-13))
(string-join '("a" "b" "c") "-")   ;  "a-b-c"

lastindexof

see #rfind

left

/* Examples in REXX */
left("abcde", 3)         /* returns "abc"      */
left("abcde", 8)         /* returns "abcde   " */
left("abcde", 8, "*")    /* returns "abcde***" */

; Examples in Scheme
(use-modules (srfi srfi-13))
(string-take "abcde", 3) ;  returns "abc" 
(string-take "abcde", 8) ;  error

' Examples in Visual Basic
Left("sandroguidi", 3)   '  returns "san" 
Left("sandroguidi", 100) '  returns "sandroguidi"

// Examples in Ya
"abcde"[0..3] // returns "abc"
"abcde"[0..8] // returns "abcde"

len

see #length

length

// Examples in C#
"hello".Length;      // returns 5
"".Length;           // returns 0

# Examples in Erlang
string:len("hello"). %  returns 5
string:len("").      %  returns 0

# Examples in Perl
length("hello");     #  returns 5
length("");          #  returns 0

' Examples in Visual Basic
Len("hello")         '  returns 5
Len("")              '  returns 0

//Examples in Objective-C
[@"hello" Length]   //returns 5
[@"" Length]   //returns 0

-- Examples in Lua
("hello"):len() -- returns 5
#"" -- returns 0

locate

see #Find

Lowercase

// Example in C#
"Wiki means fast?".ToLower();        // "wiki means fast?"

; Example in Scheme
(use-modules (srfi srfi-13))
(string-downcase "Wiki means fast?") ;  "wiki means fast?"

/* Example in C */
#include <ctype.h>
#include <stdio.h>
int main(void) {
    char string[] = "Wiki means fast?";
    int i;
    for (i = 0; i < sizeof(string) - 1; ++i) {
        /* transform characters in place, one by one */ 
        string[i] = tolower(string[i]);
    }
    puts(string);                       /* "wiki means fast?" */
    return 0;
}

mid

see #substring

partition

# Examples in Python
"Spam eggs spam spam and ham".partition('spam')   # ('Spam eggs ', 'spam', ' spam and ham')
"Spam eggs spam spam and ham".partition('X')      # ('Spam eggs spam spam and ham', "", "")

# Examples in Perl
split /(spam)/'Spam eggs spam spam and ham',2;   # ('Spam eggs ', 'spam', ' spam and ham');
split /(X)/'Spam eggs spam spam and ham',2;      # ('Spam eggs spam spam and ham');

replace

// Examples in C#
"effffff".Replace("f", "jump");     // returns "ejumpjumpjumpjumpjumpjump"
"blah".Replace("z", "y");           // returns "blah"

// Examples in Java
"effffff".replace("f", "jump");     // returns "ejumpjumpjumpjumpjumpjump"
"effffff".replaceAll("f*", "jump"); // returns "ejump"

' Examples in Visual Basic
Replace("effffff", "f", "jump")     '  returns "ejumpjumpjumpjumpjumpjump"
Replace("blah", "z", "y")           '  returns "blah"

# Examples in Windows PowerShell
"effffff" -replace "f", "jump"      #  returns "ejumpjumpjumpjumpjumpjump"
"effffff" -replace "f*", "jump"     #  returns "ejump"

reverse

" Example in Smalltalk "
'hello' reversed             " returns 'olleh' "

# Example in Perl
reverse "hello"              # returns "olleh"

# Example in Python
"hello"[::-1]                # returns "olleh"

; Example in Scheme
(use-modules (srfi srfi-13))
(string-reverse "hello")     ; returns "olleh"

rfind

; Examples in Common Lisp
(search "e" "Hello mate" :from-end t)     ;  returns 9
(search "z" "word" :from-end t)           ;  returns NIL

// Examples in C#
"Hello mate".LastIndexOf("e");           // returns 9
"Hello mate".LastIndexOf("e", 4);        // returns 1
"word".LastIndexOf("z");                 // returns -1

' Examples in Visual Basic
InStrRev("Hello mate", "e")              '  returns 10
InStrRev(5, "Hello mate", "e")           '  returns 2
InStrRev("word", "z")                    '  returns 0

right

/* Examples in REXX */
right("abcde", 3)              /* returns "cde"      */
right("abcde", 8)              /* returns "   abcde" */
right("abcde", 8, "*")         /* returns "***abcde" */

; Examples in Scheme
(use-modules (srfi srfi-13))
(string-take-right "abcde", 3) ;  returns "cde" 
(string-take-right "abcde", 8) ;  error

' Examples in Visual Basic
Right("sandroguidi", 3)        '  returns "idi" 
Right("sandroguidi", 100)      '  returns "sandroguidi"

// Examples in Java; extract rightmost 4 characters
String str = "CarDoor";
str.substring(str.length()-4); // returns 'Door'

rpartition

# Examples in Python
"Spam eggs spam spam and ham".rpartition('spam')  ### ('Spam eggs spam ', 'spam', ' and ham')
"Spam eggs spam spam and ham".rpartition('X')     ### ("", "", 'Spam eggs spam spam and ham')

slice

see #substring

split

// Example in C#
"abc,defgh,ijk".Split(',');                 // {"abc", "defgh", "ijk"}
"abc,defgh;ijk".Split(',', ';');            // {"abc", "defgh", "ijk"}

% Example in Erlang
string:tokens("abc;defgh;ijk", ";").        %  ["abc", "defgh", "ijk"]

// Examples in Java
"abc,defgh,ijk".split(",");                 // {"abc", "defgh", "ijk"}
"abc,defgh;ijk".split(",|;");               // {"abc", "defgh", "ijk"}

# Example in Pascal
var
  lStrings: TStringList;
  lStr: string;
begin
  lStrings := TStringList.Create;
  lStrings.Delimiter := ',';
  lStrings.DelimitedText := 'abc,defgh,ijk';
  lStr := lStrings.Strings[0]; // 'abc'
  lStr := lStrings.Strings[1]; // 'defgh'
  lStr := lStrings.Strings[2]; // 'ijk'
end;

# Examples in Perl
split(/spam/, 'Spam eggs spam spam and ham'); # ('Spam eggs ', ' ', ' and ham')
split(/X/, 'Spam eggs spam spam and ham');    #  ('Spam eggs spam spam and ham')

sprintf

see #Format

strip

see #trim

strcmp

see #Compare (integer result)

substring

// Examples in C#
"abc".Substring(1, 1):      // returns "b"
"abc".Substring(1, 2);      // returns "bc"
"abc".Substring(1, 6);      // error

;; Examples in Common Lisp
(subseq "abc" 1 2)          ; returns "b"
(subseq "abc" 2)            ; returns "c"

% Examples in Erlang
string:substr("abc", 2, 1). %  returns "b"
string:substr("abc", 2).    %  returns "bc"

# Examples in Python
"abc"[1:2]                 #  returns "b"
"abc"[1:3]                 #  returns "bc"

/* Examples in REXX */
substr("abc", 2, 1)         /* returns "b"      */
substr("abc", 2)            /* returns "bc"     */
substr("abc", 2, 6)         /* returns "bc    " */
substr("abc", 2, 6, "*")    /* returns "bc****" */

Uppercase

// Example in C#
"Wiki means fast?".ToUpper();      // "WIKI MEANS FAST?"

/* Example in REXX */
translate("Wiki means fast?")      /* "WIKI MEANS FAST?" */
 
/* Example #2 */
A='This is an example.'
UPPER A                            /* "THIS IS AN EXAMPLE." */
 
/* Example #3 */
A='upper using Translate Function.'
Translate UPPER VAR A Z            /* Z="UPPER USING TRANSLATE FUNCTION." */

; Example in Scheme
(use-modules (srfi srfi-13))
(string-upcase "Wiki means fast?") ;  "WIKI MEANS FAST?"

' Example in Visual Basic
UCase("Wiki means fast?")          '  "WIKI MEANS FAST?"

trim

trim or strip is used to remove whitespace from the beginning, end, or both beginning and end, of a string.

References

External links

• Perl String Functions
• Python 2 String Methods
• Python 3 String Methods
• Scheme String Procedures
• Erlang String Functions
• .NET String Methods and Properties
• Ruby String Class
• PHP String functions
• java.lang.String members
• Haskell Hierarchical Libraries
• Arrays in D (in D strings are regular arrays)
• std.string from Phobos (D standard library)
• Lua String Functions
• OCaml String module
• Common Lisp String manipulation
• FreeBASIC String Functions
• Reference.wolfram.com