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