Pascal - Strings


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The string in Pascal is actually a sequence of characters with an optional size specification. The characters could be numeric, letters, blank, special characters or a combination of all. Extended Pascal provides numerous types of string objects depending upon the system and implementation. We will discuss more common types of strings used in programs.

You can define a string in many ways −

  • Character arrays − This is a character string which is a sequence of zero or more byte-sized characters enclosed in single quotes.

  • String variables − The variable of String type, as defined in Turbo Pascal.

  • Short strings − The variable of String type with size specification.

  • Null terminated strings − The variable of pchar type.

  • AnsiStrings − Ansistrings are strings that have no length limit.

Pascal provides only one string operator, string concatenation operator (+).

Examples

The following program prints first four kinds of strings. We will use AnsiStrings in the next example.

program exString;
var
   greetings: string;
   name: packed array [1..10] of char;
   organisation: string[10];
   message: pchar;

begin
   greetings := 'Hello ';
   message := 'Good Day!';
   
   writeln('Please Enter your Name');
   readln(name);
   
   writeln('Please Enter the name of your Organisation');
   readln(organisation);
   
   writeln(greetings, name, ' from ', organisation);
   writeln(message); 
end.

When the above code is compiled and executed, it produces the following result −

Please Enter your Name
John Smith
Please Enter the name of your Organisation
Infotech
Hello John Smith from Infotech

Following example makes use of few more functions, let's see −

program exString;
uses sysutils;
var
   str1, str2, str3 : ansistring;
   str4: string;
   len: integer;

begin
   str1 := 'Hello ';
   str2 := 'There!';
   
   (* copy str1 into str3 *)
   str3 := str1;
   writeln('appendstr( str3, str1) :  ', str3 );
   
   (* concatenates str1 and str2 *)
   appendstr( str1, str2);
   writeln( 'appendstr( str1, str2) ' , str1 );
   str4 := str1 + str2;
   writeln('Now str4 is: ', str4);
   
   (* total lenghth of str4 after concatenation  *)
   len := byte(str4[0]);
   writeln('Length of the final string str4: ', len); 
end.

When the above code is compiled and executed, it produces the following result −

appendstr( str3, str1) : Hello
appendstr( str1, str2) : Hello There!
Now str4 is: Hello There! There!
Length of the final string str4: 18

Pascal String Functions and Procedures

Pascal supports a wide range of functions and procedures that manipulate strings. These subprograms vary implement-wise. Here, we are listing various string manipulating subprograms provided by Free Pascal −

Sr.No. Function & Purpose
1

function AnsiCompareStr(const S1: ; const S2:):Integer;

Compares two strings

2

function AnsiCompareText(const S1: ; const S2:):Integer;

Compares two strings, case insensitive

3

function AnsiExtractQuotedStr(var Src: PChar; Quote: Char):;

Removes quotes from string

4

function AnsiLastChar(const S:):PChar;

Gets last character of string

5

function AnsiLowerCase(const s:):

Converts string to all-lowercase

6

function AnsiQuotedStr(const S: ; Quote: Char):;

Quotes a string

7

function AnsiStrComp(S1: PChar;S2: PChar):Integer;

Compares strings case-sensitive

8

function AnsiStrIComp(S1: PChar; S2: PChar):Integer;

Compares strings case-insensitive

9

function AnsiStrLComp(S1: PChar; S2: PChar; MaxLen: Cardinal):Integer;

Compares L characters of strings case sensitive

10

function AnsiStrLIComp(S1: PChar; S2: PChar; MaxLen: Cardinal):Integer;

Compares L characters of strings case insensitive

11

function AnsiStrLastChar(Str: PChar):PChar;

Gets last character of string

12

function AnsiStrLower(Str: PChar):PChar;

Converts string to all-lowercase

13

function AnsiStrUpper(Str: PChar):PChar;

Converts string to all-uppercase

14

function AnsiUpperCase(const s:):;

Converts string to all-uppercase

15

procedure AppendStr(var Dest: ; const S:);

Appends 2 strings

16

procedure AssignStr(var P: PString; const S:);

Assigns value of strings on heap

17

function CompareStr(const S1: ; const S2:):Integer; overload;

Compares two strings case sensitive

18

function CompareText(const S1: ; const S2:):Integer;

Compares two strings case insensitive

19 procedure DisposeStr(S: PString); overload;

Removes string from heap

20

procedure DisposeStr(S: PShortString); overload;

Removes string from heap

21

function IsValidIdent( const Ident:):Boolean;

Is string a valid pascal identifier

22

function LastDelimiter(const Delimiters: ; const S:):Integer;

Last occurrence of character in a string

23

function LeftStr(const S: ; Count: Integer):;

Gets first N characters of a string

24

function LoadStr(Ident: Integer):;

Loads string from resources

25

function LowerCase(const s: ):; overload;

Converts string to all-lowercase

26

function LowerCase(const V: variant ):; overload;

Converts string to all-lowercase

27

function NewStr(const S:):PString; overload;

Allocates new string on heap

28

function RightStr(const S: ; Count: Integer):;

Gets last N characters of a string

29

function StrAlloc(Size: Cardinal):PChar;

Allocates memory for string

30

function StrBufSize(Str: PChar):SizeUInt;

Reserves memory for a string

31

procedure StrDispose(Str: PChar);

Removes string from heap

32

function StrPas(Str: PChar):;

Converts PChar to pascal string

33

function StrPCopy(Dest: PChar; Source:):PChar;

Copies pascal string

34

function StrPLCopy(Dest: PChar; Source: ; MaxLen: SizeUInt):PChar;

Copies N bytes of pascal string

35

function UpperCase(const s:):;

Converts string to all-uppercase



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