Strings / String Manipulation¶

String is a kind of sequence of characters/digits and it is one of most common types of programming languages. This section aims to introduce some key features of string type and most used string manipulation functions.

Some Facts About Strings¶

In TROIA, STRING type is used for both string and char type compared to other programming languages such as java etc. There is not hard-coded maximum length (character-limit) of string typed variables and hard code strings, so if you have trouble about maximum character length, possibly its about your length of your database table, table column or editor length etc.

String variables are able to store all kind of characters and digits.

As mentioned previous sections, undefined variables are returns their name. It seems they are STRING variables but undefined variable’s are not string, they are just undefined symbols that stores their name.

Single quote character (’) is used to limit hard code strings in TROIA code.

Escaping & Special Characters¶

To insert a meaningful character (such as ‘) to a hard code string, escape character are used in different programming languages. Escape character changes the interpretation method of following characters. For example ‘ (single quote) character limits hard code strings, when programmer wants to insert a single quote, he/she must use an escape character.

TROIA does not support escape characters for hard code strings. Instead of escaping, TOCHAR() system function is used to insert special characters to a hard code string. TOCHAR() function gets decimal ASCII correspondent of requested character and returns a single character as string. For example programmer must pass 39 to get a single quote character or 10 for a newline character.

OBJECT:
        STRING STRVAR;

STRVAR = 'First line, it contains ' + TOCHAR(39) + ' (single quote).';
STRVAR = STRVAR + TOCHAR(10) + 'Second line.';

/*
value of STRVAR must like:

First line, it contains ' (single quote).
This is second line.

*/

Basic String Functions¶

Here is system functions that returns basic information about string variables:

STRLEN	Returns the length of given string
STRPOS()	Returns index of given string inside another
ISNUMERIC()	Check string whether all characters are numeric
STRLIKE()	Compares string with given pattern like SQL LIKE op.

and most used system functions to modify strings:

TRIM()	Removes white spaces from the beginning and the end.
REPLACE()	Replaces a given string with another
STRSTR()	Returns substring of string with index and length
LOWERCASE()	Returns lowercase of given string with given language
UPPERCASE()	Returns uppercase of given string with given language

For more string manipulation functions or more information about these functions (like parameter order and return types etc), please see String Manipulation section of TROIA Help.

Base64 Encoding/Decoding¶

Base64 is a kind binary-to-text encoding scheme that represent binary data in an ASCII string format. Resulting string contains only 64 kind of characters which contains only a-z, A-Z, 0-9, +, / characters so the resulting string can be stored on or transferred between ‘ASCII only’ environments.

To encode strings to Base64 BASE64ENCODE() system function is used, to convert a base64 string to a troia string BASE64DECODE() system function is used. Both encoding and decoding requires an encoding like ‘UTF-8’ etc to convert string to binary or binary to string. For more information about BASE64ENCODE() & BASE64DECODE() functions please see TROIA help documents.

Here is an encoding and decoding example:

OBJECT:
        STRING STRVALUE,
        STRING STRBASE64,
        STRING STRDECODED;

STRVALUE = 'Programming With TROIA';
STRBASE64 = BASE64ENCODE(STRVALUE, 'UTF-8');
STRDECODED = BASE64DECODE(STRBASE64, 'UTF-8');

Hashing Strings¶

Hashing is an operation that maps an arbitrary size data to fixed size. Resulting hash value can not be decoded to original data, because hash values of different input values can be identical. For example length of given string can be thought as a kind of hashing. Most used hashing algorithms are MD5,SHA1, MD2 etc.

In TROIA, GETDIGEST() function is used to hash using multiple algorithms. For more information and supported algorithms please see TROIA Help.

OBJECT:
        STRING STRVALUE,
        STRING MD5HASH,
        STRING SHA1HASH;

STRVALUE = 'Programming With TROIA';
MD5HASH = GETDIGEST(STRVALUE, 'MD5');
SHA1HASH = GETDIGEST(STRVALUE, 'SHA1');

String Concatenation¶

As default + operator is used to concatenate strings in TROIA, but it is not recommended to use + operator to build large strings because of performance issues.

OBJECT:
        STRING FINALSTRING;

FINALSTRING = 'Hello ' + ' World.';

Performance problem of string concatenation is not about only ‘+’ operator, its also about STRING type. To solve performance issues, programmers must use STRINGBUILDER data type which is mentioned in previous sections. Defining a STRINGBUILDER is not different from defining a STRING variable. To append/concat a given string to a STRINGBUILDER, APPENDSTRING command is used. Here is STRINGBUILDER & APPENDSTRING equivalent of previous example.

OBJECT:
        STRINGBUILDER SBFINALSTRING;

APPENDSTRING 'Hello' TO SBFINALSTRING;
APPENDSTRING ' World' TO SBFINALSTRING;

STRINGBUILDER is designed for only hi-performance string building operations, so it is not recommended to use STRINGBUILDER object instead of STRING.

To benchmark using STRING/+ and STRINGBUILDER/APPENDSTRING you can write a while loop that makes one thousand concat operation.

Looping on Strings: PARSE Command¶

To split a string into tokens (with newline or with a specific delimiter character) and do something for each token, PARSE command is used. As it is obvious PARSE command is a kind of loop statement, so BREAK and CONTINUE statements also works in parse command. Here is the basic syntax:

PARSE {mainstring} INTO {token} [DELIMITER {delimiter}]
BEGIN
        parse block
ENDPARSE;

Delimiter is an optional parameter; if it is not specified newline (linefeed, n) character is used and main string is splitted into lines.

The sample below tries to calculate length of each line.

OBJECT:
        STRING STRMAINSTRING,
        STRING STRTOKEN;

OBJECT:
        INTEGER NLINECOUNT,
        STRING STRRESULT;

NLINECOUNT = 0;
STRRESULT = '';

STRMAINSTRING = 'I do not trust words.';
STRMAINSTRING = STRMAINSTRING + TOCHAR(10) + 'I trust actions.';

PARSE STRMAINSTRING INTO STRTOKEN
BEGIN
        NLINECOUNT = NLINECOUNT + 1;

        STRRESULT = STRRESULT + 'Line ' + NLINECOUNT + ':' + STRLEN(STRTOKEN);
        STRRESULT = STRRESULT + ' char(s).' + TOCHAR(10);

ENDPARSE;

Exercise 1: Basic String Functions¶

Here is a simple string functions example, please try to find return values after each function call.

OBJECT:
        STRING STRMESSAGE,
        INTEGER NINDEX;

STRMESSAGE = ' Hello TROIA ' + TOCHAR(10);

/* remove whitespaces */
STRMESSAGE = TRIM(STRMESSAGE);

/* replace word 'TROIA' with 'world' */
STRMESSAGE = REPLACE(STRMESSAGE, 'TROIA', 'World');

/* calculate index of 'world' */
NINDEX = STRPOS(STRMESSAGE, 'World');

/* get first 5 character*/
STRMESSAGE = STRSTR(STRMESSAGE, 0, 5);

Exercise 2: List Numeric Tokens¶

OBJECT:
        STRINGBUILDER SB,
        STRING STRNEWLINE,
        STRING MAINSTRING,
        STRING TOKEN;

SB = '';
STRNEWLINE = TOCHAR(10);
MAINSTRING = '1|A|2|B|3|C|4|D|5|E';

PARSE MAINSTRING INTO TOKEN DELIMITER '|'
BEGIN

        IF !ISNUMERIC(TOKEN) THEN
                CONTINUE;
        ENDIF;

        APPENDSTRING TOKEN TO SB;
        APPENDSTRING ' is a number.' TO SB;
        APPENDSTRING STRNEWLINE TO SB;
ENDPARSE;