Pascal - Strings

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Category: Chapter 3

Published: Sunday, 14 April 2013 16:21

Written by Sternas Stefanos

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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 commonly 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 (+).

 

1. 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 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 following result:

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

 

2. 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:

S.N.	Function & Purpose
1	function AnsiCompareStr( const S1: ; const S2: ):Integer; Compare two strings
2	function AnsiCompareText( const S1: ; const S2: ):Integer; Compare two strings, case insensitive
3	function AnsiExtractQuotedStr( var Src: PChar; Quote: Char ):; Removes quotes from string
4	function AnsiLastChar( const S: ):PChar; Get last character of string
5	function AnsiLowerCase( const s: ): Convert string to all-lowercase
6	function AnsiQuotedStr( const S: ; Quote: Char ):; Qoutes a string
7	function AnsiStrComp( S1: PChar; S2: PChar ):Integer; Compare strings case-sensitive
8	function AnsiStrIComp( S1: PChar; S2: PChar ):Integer; Compare strings case-insensitive
9	function AnsiStrLComp( S1: PChar; S2: PChar; MaxLen: Cardinal ):Integer; Compare L characters of strings case sensitive
10	function AnsiStrLIComp( S1: PChar; S2: PChar; MaxLen: Cardinal ):Integer; Compare L characters of strings case insensitive
11	function AnsiStrLastChar( Str: PChar ):PChar; Get last character of string
12	function AnsiStrLower( Str: PChar ):PChar; Convert string to all-lowercase
13	function AnsiStrUpper( Str: PChar ):PChar; Convert string to all-uppercase
14	function AnsiUpperCase( const s: ):; Convert string to all-uppercase
15	procedure AppendStr( var Dest: ; const S: ); Append 2 strings
16	procedure AssignStr( var P: PString; const S: ); Assign value of strings on heap
17	function CompareStr( const S1: ; const S2: ):Integer; overload; Compare two strings case sensitive
18	function CompareText( const S1: ; const S2: ):Integer; Compare two strings case insensitive
19	procedure DisposeStr( S: PString ); overload; Remove string from heap
20	procedure DisposeStr( S: PShortString ); overload; Remove string from heap
21	function IsValidIdent( const Ident: ):Boolean; Is string a valid pascal identifier
22	function LastDelimiter( const Delimiters: ; const S: ):Integer; Last occurance of character in a string
23	function LeftStr( const S: ; Count: Integer ):; Get first N characters of a string
24	function LoadStr( Ident: Integer ):; Load string from resources
25	function LowerCase( const s: ):; overload; Convert string to all-lowercase
26	function LowerCase( const V: variant ):; overload; Convert string to all-lowercase
27	function NewStr( const S: ):PString; overload; Allocate new string on heap
28	function RightStr( const S: ; Count: Integer ):; Get last N characters of a string
29	function StrAlloc( Size: Cardinal ):PChar; Allocate memory for string
30	function StrBufSize( Str: PChar ):SizeUInt; Reserve memory for a string
31	procedure StrDispose( Str: PChar ); Remove string from heap
32	function StrPas( Str: PChar ):; Convert PChar to pascal string
33	function StrPCopy( Dest: PChar; Source: ):PChar; Copy pascal string
34	function StrPLCopy( Dest: PChar; Source: ; MaxLen: SizeUInt ):PChar; Copy N bytes of pascal string
35	function UpperCase( const s: ):; Convert string to all-uppercase

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