String functions (programming)

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"String functions" redirects here. For string functions in formal language theory, see String operations.
This article is part of the
Programming Language Comparison
series.
General Comparison
Basic Syntax
Basic Instructions
Arrays
Associative arrays
String Operations
String Functions
Object-oriented programming
Database access
Evaluation strategy
List of "hello world" programs
Comparison of ALGOL 68 and C++
Compatibility of C and C++
Comparison of C and Pascal
Comparison of C++ and Java
Comparison of C# and Java
Comparison of C# and Visual Basic .NET
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String functions are used in computer programming languages to manipulate a string or query information about a string (some do both).

Most computer programming languages that have a string datatype will have some string functions although it should be noted that 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 both Prolog and Erlang, a string is represented as a list (of character codes), therefore all list-manipulation procedures are applicable, though the latter also implements a set of such procedures that are string-specific.

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

eg. 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.

Contents

[edit] Common String Functions (multi language reference)

Here is a list of common string functions which are found in other languages. Any other equivalent functions used by other languages are also listed. 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.

[edit] CharAt

Definition charAt(string,integer) returns character.
Description Returns character at index in the string.
Equivalent See substring of length 1 character.
Format Languages
string[i] C, C++, C#, Python, PHP, Ruby, Windows PowerShell
string(i) Ada
string.Chars(i) VB.NET (index starts at position 0)
string.charAt(i) Java, JavaScript
string.[i] OCaml
string !! i Haskell
(string-ref string i) Scheme
(char string i) Common Lisp
substr(string, i, 1) Perl
string.at(i) C++ (std::string only) (w/ bounds checking)

[edit] Compare (integer result)

Definition compare(string1,string2) returns integer.
Description Compares two strings to each other. If they are equivalent, a zero is returned. Otherwise, most of these routines will return a positive or negative result corresponding to whether string1 is lexicographically greater than, or less than, respectively, than string2. The exceptions are the Scheme and REXX routines which return the index of the first mismatch.
Format Languages
cmp(string1, string2) Python
strcmp(string1, string2) C, PHP
StrComp(string1, string2) VB
string1 cmp string2 Perl
string1 <=> string2 Ruby
string1.compare(string2) C++
compare(string1, string2) REXX
CompareStr(string1, string2) Pascal, Object Pascal (Delphi)
string1.compareTo(string2) Java
string1.CompareTo(string2) VB .NET, C#
(string-compare string1 string2 p< p= p>) Scheme
compare string1 string2 OCaml
compare string1 string2 Haskell (returns LT, EQ, or GT)
[string]::Compare(string1, string2) Windows PowerShell 
# 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)

[edit] Compare (integer result, fast/non-human ordering)

Definition compare(string1,string2) returns integer.
Description Compares two strings to each other. If they are equivalent, a zero is returned. Otherwise, most of these routines will return a positive or negative result corresponding to whether string1 is greater than, or less than, respectively, than string2. The reason for the difference between this and #Compare (integer result) is that no ordering guarantees are given, leaving the implementation to do whatever ordering is fastest, a common implementation is to order by length and then by byte value (which can be significantly faster, but much less useful to humans).
Format Languages
if (!(ret = (string1_len - string2_len))) ret = memcmp(string1, string2, string1_len) C
ustr_cmp_fast(string1, string2) Ustr string library
(length(string1) <=> length(string2) ¦¦ string1 cmp string2) Perl
cmp(len(string1), len(string2)) or cmp(string1, string2) Python
(Length(string1) <> Length(string2)) or CompareStr(string1, string2) Pascal, Object Pascal (Delphi)

[edit] Compare (relational operator-based, Boolean result)

Definition string1 op string2 OR (compare string1 string2) returns Boolean.
Description Lexicographically compares two strings using a relational operator or function. Boolean result returned.
Format Languages
string1 op string2, where op can be any of =, <>, <, >, <= and >= Pascal, Object Pascal (Delphi), OCaml, VB .NET
(stringX? string1 string2), where X can be any of =, -ci=, <>, -ci<>, <, -ci<, >, -ci>, <=, -ci<=, >= and -ci>= (operators starting with '-ci' are case-insensitive) Scheme
(stringX string1 string2), where X can be any of =, -equal, /=, -not-equal, <, -lessp, >, -greaterp, <=, -not-greaterp, >= and -not-lessp (the verbal operators are case-insensitive) Common Lisp
string1 op string2, where op can be any of =, \=, <, >, <= and >= REXX
string1 op string2, where op can be any of =, /=, <, >, <= and >= Ada
string1 op string2, where op can be any of ==, /=, <, >, =< and >= Erlang
string1 op string2, where op can be any of ==, /=, <, >, <= and >= Haskell
string1 op string2, where op can be any of eq, ne, lt, gt, le and ge Perl
string1 op string2, where op can be any of ==, !=, <, >, <= and >= C++ (std::string only), C#, JavaScript, Python
string1 op string2, where op can be any of -eq, -ceq, -ne, -cne, -lt, -clt, -gt, -cgt, -le, -cle, -ge, and -cge (operators starting with 'c' are case-sensitive) Windows PowerShell 
% Example in Erlang
"hello" > "world".            % returns: false

[edit] Concatenation

Main article: Concatenation
Definition concatenate(string1,string2) returns string.
Description Concatenates (joins) two strings to each other, returning the combined string. Note that some languages like C have mutable strings, so really the second string is being appended to the first string and the mutated string is returned.
Format Languages
string1 & string2 Ada, VB, VB .NET
strcat(string1, string2) C, C++
string1 . string2 Perl, PHP
string1 + string2 C++ (std::string only), C#, Pascal, Object Pascal (Delphi), Java, JavaScript, Windows PowerShell, Python
(string-append string1 string2) Scheme
(concatenate 'string string1 string2) Common Lisp
string1 || string2 REXX,Fortran
string1 ++ string2 Erlang
string1 ^ string2 OCaml
string1 ++ string2 Haskell

[edit] 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 programer but is often a significantly more expensive operation, this is especially true when using "C-strings".

Format Languages
string1 == string2 Python, C++(std::string only), C#, JavaScript PHP, Ruby, Erlang, Haskell
strcmp(string1, string2) == 0 C
(string=? string1 string2) Scheme
(string= string1 string2) Common Lisp
string1 = string2 Ada, Object Pascal (Delphi), OCaml, Pascal, REXX, VB, VB .NET
test string1 = string2, or
[ string1 = string2 ]		 Bourne Shell
string1 eq string2 Perl
string1.equals(string2) Java
string1 -eq string2, or
[string]::Equals(string1, string2)		 Windows PowerShell

[edit] Find

Definition find(string,substring) returns integer
Description Returns the position of the start of the first occurrence of substring in string. If the substring is not found most of these routines return an invalid index value – -1 where indexes are 0-based, 0 where they are 1-based – or some value to be interpreted as Boolean FALSE.
Related instrrev
Format Languages If not found
InStr([startpos,]string,substring) VB (startpos optional) (positions start at 1) returns 0
index(string,substring) AWK returns 0
index(string,substring[,startpos]) Perl returns -1
strpos(string,substring[,startpos]) PHP returns FALSE
locate(string, substring) Ingres returns string length + 1
strstr(string, substring) C, C++ (returns pointer to first character) returns NULL
pos(substring, string) Pascal, Object Pascal (Delphi) returns 0
pos(substring, string[,startpos]) REXX returns 0
string.find(substring[,startpos]) C++ (std::string only) returns std::string::npos
string.find(substring[,startpos[[,endpos]]) Python returns -1
string.index(substring[,startpos]) Ruby returns nil
string.indexOf(substring[,startpos]) Java, JavaScript returns -1
string.IndexOf(substring[,startpos[, charcount]]) VB .NET, C#, Windows PowerShell returns -1
string:str(string, substring)) Erlang returns 0
(string-contains string substring) Scheme returns #f
(search substring string) Common Lisp returns NIL 
' Example in Visual Basic
InStr("Hello mate", "ell")            ' returns: 2
InStr(5, "Hello mate", "e")           ' returns: 10
InStr("word", "z")                    ' returns: 0

; Example in Scheme
(use-modules (srfi srfi-13))
(string-contains "Hello mate", "ell") ; returns: 1
(string-contains "word", "z")         ; returns: #f

[edit] Format

Definition format(formatstring, items) returns string
Description Returns the formatted string representation of one or more items. See sprintf for more information.
Format Languages
Format(item, formatstring) VB
sprintf(formatstring, items) Perl, PHP, Ruby
sprintf(outputstring, formatstring, items) C, C++
printf -v outputstring formatstring items Unix
formatstring % (items) Python
Printf.sprintf formatstring items OCaml
Text.Printf.printf formatstring items Haskell (GHC)
String.format(formatstring, items) Java
String.Format(formatstring, items) VB .NET, C#, Windows PowerShell
(format formatstring items) Scheme
(format nil formatstring items) Common Lisp

[edit] Inequality

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

Format Languages
string1 <> string2 VB,VB .NET, Pascal, Object Pascal (Delphi), OCaml
string1 ne string2 Perl
(string<>? string1 string2) Scheme
(string/= string1 string2)) Common Lisp
string1 != string2 C++ (std::string only), C#, JavaScript, Python
string1 \= string2 REXX
string1 /= string2 Ada, Erlang, Haskell
test string1 != string2, or
[ string1 != string2 ]		 Bourne Shell
string1 -ne string2, or
![string]::Equals(string1, string2)		 Windows PowerShell

[edit] index

see #Find

[edit] indexof

see #Find

[edit] instr

see #Find

[edit] instrrev

see #rfind

[edit] join

Definition join(separator, list_of_strings) joins a list of strings with a separator
Description Joins the list of strings into a new string, with the separator string between each of the substrings. Opposite of split.
Format Languages
join(separator, list_of_strings) Perl
implode(separator, array_of_strings) PHP
separator.join(sequence_of_strings) Python
array_of_strings.join(separator) Ruby, JavaScript
(string-join array_of_strings separator) Scheme
(format nil "~{~a~^separator~}" array_of_strings) Common Lisp
String.concat separator list_of_strings OCaml
Data.List.intercalate separator list_of_strings Haskell (GHC)
Join(array_of_strings, separator) VB
String.Join(separator, array_of_strings) VB .NET, C#
&{$OFS=$separator; "$array_of_strings"}, or
[string]::Join(separator, array_of_strings)		 Windows PowerShell 
# Example in Python
mystr = "-".join(["a", "b", "c"])  # ('a-b-c')

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

[edit] lastindexof

see #rfind

[edit] left

Definition left(string,n) returns string
Description Returns the left n part of a string. If n is greater than the length of the string then most implementations return the whole string (exceptions exist - see code examples).
Format Languages
string (string'First .. string'First + n - 1) Ada
Left(string,n) VB
left(string,n) Ingres
left(string,n [,padchar]) REXX, Erlang
substr(string, 0, n) AWK (changes string), Perl, PHP
string[:n] Python
string[0..n - 1] Ruby
string.substr(0,n) C++
string.Substring(0,n) VB .NET, C#, Windows PowerShell
leftstr(string, n) Pascal, Object Pascal (Delphi)
string.substring(0,n) Java, JavaScript
(string-take string n) Scheme
take n string Haskell 
' Example in Visual Basic
Left("sandroguidi", 3)   ' returns: "san" 
Left("sandroguidi", 100) ' returns: "sandroguidi"

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

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

[edit] len

see #length


[edit] length

Definition length(string) returns an integer number
Description Returns the length of a string (not counting the null terminator or any other of the string's internal structural information). An empty string returns a length of 0.
Format Languages
string'Length Ada
length(string) Perl, Ingres, Pascal, Object Pascal (Delphi), REXX
len(string) Python, Erlang
Len(string) VB
string.Length VB .NET, C#
string.size OR string.length Ruby, Windows PowerShell
strlen(string) C, C++, PHP
string.length() C++ (std::string only), Java
string.length JavaScript
(string-length string) Scheme
(length string) Common Lisp
String.length string OCaml
length string Haskell 
# Examples in Perl
length("hello")      # returns: 5
length("")           # returns: 0

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

[edit] locate

see #Find

[edit] Lowercase

see also #Uppercase


[edit] mid

see #substring


[edit] partition

Definition <string>.partition(separator) returns the sub-string before the separator; the separator; then the sub-string after the separator.
Description Splits the given string by the separator and returns the three substrings that together make the original.
Format Languages
string.partition(separator) Python, Ruby 
# 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', "", "")

[edit] replace

Definition replace(string, find, replace) returns string
Description Returns a string the with find occurrences changed to replace.
Format Languages
changestr(find, string, replace) REXX
Replace(string, find, replace) VB
string.Replace(find, replace) VB .NET, C#
str_replace(find, replace, string) PHP
string.replace(find, replace) Python, Java (1.5+)
string.replaceAll(find_regex, replace)[1] Java
string.gsub(find, replace) Ruby
string =~ s/find_regex/replace/g[1] Perl
string.replace(find, replace, "g") or
string.replace(/find_regex/g, replace)[1]		 JavaScript
echo "string" | sed 's/find_regex/replace/g'[1] Unix
string.replace(find, replace), or
string -replace find_regex, replace[1]		 Windows PowerShell 
' Examples in Visual Basic
Replace("effffff", "f", "jump") ' returns "ejumpjumpjumpjumpjumpjump"
Replace("blah", "z", "y")       ' returns "blah".

[edit] reverse

Definition reverse(string)
Description Reverses the order of the characters in the string.
Format Languages
reverse string Perl, Haskell
strrev(string) PHP
string[::-1] Python
(string-reverse string) Scheme
(reverse string) Common Lisp
string.reverse Ruby
new StringBuilder(string).reverse().toString() Java
std::reverse(string.begin(), string.end()); C++ (std::string only)
StrReverse(string) VB
New String(Array.Reverse(string.ToCharArray())) VB .NET
new string(Array.Reverse(string.ToCharArray())) C#

[edit] rfind

Definition rfind(string,substring) returns integer
Description Returns the position of the start of the last occurrence of substring in string. If the substring is not found most of these routines return an invalid index value – -1 where indexes are 0-based, 0 where they are 1-based – or some value to be interpreted as Boolean FALSE.
Related instr
Format Languages If not found
InStrRev([startpos, ]string,substring) VB returns 0
rindex(string,substring[,startpos]) Perl returns -1
strrpos(string,substring[,startpos]) PHP returns FALSE
string.rfind(substring[,startpos]) C++ (std::string only) returns std::string::npos
string.rfind(substring[,startpos]) Python returns -1
string.lastIndexOf(substring[,startpos]) Java, JavaScript returns -1
string.LastIndexOf(substring[,startpos[, charcount]]) VB .NET, C#, Windows PowerShell returns -1
(search substring string :from-end) Common Lisp returns NIL

[edit] right

Definition right(string,n) returns string
Description Returns the right n part of a string. If n is greater than the length of the string then most implementations return the whole string (exceptions exist - see code examples).
Format Languages
string (string'Last - n + 1 .. string'Last) Ada
Right(string,n) VB
right(string,n) Ingres
right(string,n [,padchar]) REXX, Erlang
substr(string,-n) Perl, PHP
string[-n:] Python
(string-take-right string n) Scheme 
' Example in Visual Basic
Right("sandroguidi", 3)        ' returns: "idi" 
Right("sandroguidi", 100)      ' returns: "sandroguidi"

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

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

[edit] rpartition

Definition <string>.rpartition(separator) Searches for the separator from right-to-left within the string then returns the sub-string before the separator; the separator; then the sub-string after the separator.
Description Splits the given string by the right-most separator and returns the three substrings that together make the original.
Format Languages
string.rpartition(separator) Python, Ruby 
# 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')

[edit] slice

see #substring

[edit] split

Definition <string>.split(separator[, limit]) splits a string on separator, optionally only up to a limited number of substrings
Description Splits the given string by occurrences of the separator (itself a string) and returns a list (or array) of the substrings. If limit is given, after limit - 1 separators have been read, the rest of the string is made into the last substring, regardless of whether it has any separators in it. The Scheme and Erlang implementations are similar but differ in several ways. Opposite of join.
Format Languages
split(/separator/, string[, limit]) Perl
explode(separator, string[, limit]) PHP
string.split(separator[, limit]) Javascript, Java, Python, Ruby
tokens(string, sepchars) Erlang
(string-tokenize string[ charset[ start[ end]]]) Scheme
Split(string, sepchars[, limit]) VB
string.Split(sepchars[, limit[, options]]) VB .NET, C#
string.split(separator) Windows PowerShell 
# Example in Python
"Spam eggs spam spam and ham".split('spam') ### ('Spam eggs ', ' ', ' and ham')
"Spam eggs spam spam and ham".split('X')    ### ('Spam eggs spam spam and ham')

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

; Example in Scheme
(use-modules (srfi srfi-13))
(string-tokenize "abc,defgh,ijk" char-set:letter)    ; ("abc" "defgh" "ijk")

[edit] sprintf

see #Format

[edit] strip

see #trim


[edit] strcmp

see #Compare (integer result)


[edit] substring

Definition substr(string, startpos, numChars) returns string
Description Returns a substring of string starting at startpos of length numChars. The resulting string is truncated if there are fewer than numChars characters beyond the starting point
Format Languages
string (startpos .. startpos + numChars - 1) Ada
Mid(string, startpos, numChars) VB
substr(string, startpos, numChars) AWK (changes string), Perl, PHP
substr(string, startpos [,numChars, padChar]) REXX
string[startpos:startpos + numChars - 1] Python
string[startpos, numChars] Ruby
string.slice(startpos, endpos) JavaScript
string.substr(startpos, numChars) C++ (std::string only)
string.Substring(startpos, numChars) VB .NET, C#, Windows PowerShell
string.substring(startpos, endpos) Java, JavaScript
copy(string, startpos, numChars) Delphi
(string-copy string startpos endpos) Scheme
(subseq string startpos endpos) Common Lisp
String.sub string startpos numChars Ocaml
substr(string, startpos, numChars) Erlang
char result[numChars+1] = "";
strncat(result, string + startpos, numChars);		 C
take numChars $ drop startpos string Haskell 
# Example in AWK
substr("abc", 2, 1)         # returns: "b"
substr("abc", 2, 6)         # returns: "bc"

/* Example 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****" */

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

' Example in Visual Basic .NET
' -> Left(input, len) and input.Substring(0, len) are equivalent!
Dim len As Integer = 3
Dim input As String = "abcdef"
Dim expected = "abc"
'Gets the first 3 characters using Left and String.Substring
Dim withLeft As String = Left(input, len)
Dim withSubstring As String = input.Substring(0, len)
'Verify the two methods returned the expected value
Debug.Assert(withSubstring = expected AndAlso withLeft = expected)

[edit] Uppercase

Definition uppercase(string) returns string
Description Returns the string in upper case.
Format Languages
UCase(string) VB
toupper(string) AWK (changes string)
uc(string) Perl
toupper(char) C (operates on a single character)
transform(string.begin(), string.end(), result.begin(), toupper) C++ (std::string only) (result is stored in string result which is at least as long as string, and may or may not be string itself)
uppercase(string) Delphi
strtoupper(string) PHP
echo "string" | tr 'a-z' 'A-Z' Unix
translate(string) REXX
string.upper() Python
string.upcase Ruby
(string-upcase string) Scheme, Common Lisp
String.uppercase string OCaml
map Char.toUpper string Haskell
string.toUpperCase() Java, JavaScript
to_upper(string) Erlang
string.ToUpper() VB .NET, C#, Windows PowerShell 
' Example in Visual Basic
UCase("Wiki means fast?")          ' "WIKI MEANS FAST?"

/* Example in REXX */
translate("Wiki means fast?")      /* "WIKI MEANS FAST?" */

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

[edit] trim

Main article: Trim (programming)

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

[edit] Notes

  1. ^ a b c d e The "find" string in this construct is interpreted as a regular expression. Certain characters have special meaning in regular expressions. If you want to find a string literally, you need to quote the special characters.

[edit] External links

Languages