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Unicode#

A string in PeachPie is an object representing either a text or a sequence of bytes. Text natively consists of Unicode characters and is based on .NET's System.String data type.

Native support for Unicode is built into the type system, in the compiler, and in library functions. By default, all textual operations respect the Unicode semantic, allowing for safe and clean text manipulation.

The string value, however, can be both - a UTF-16 character sequence and/or a single-byte sequence.

String values are not zero-terminated, hence they can contain \0 characters without breaking strlen, echo and other string operations.

Source Files#

String literals contained in the source code are parsed with respect to the CodePage property and transformed into UTF-16 textual values. The encoding used to decode source files is UTF-8 by default.

<?php
// outputs the Unicode string
// the text is safely encoded using current output encoding
echo "Ahoj světe!";

// assigns the Unicode textual value into a variable `$value`
// Internally the value is stored safely as UTF-16
$value = "Привет мир!";

It is recommended to save the source files using UTF-8 encoding, eventually including the UTF Signature (BOM). The BOM is automatically ignored from the source files. If a file is saved using a different encoding, specify the encoding using the CodePage property in order to decode the textual values correctly. An incorrect encoding may result in a compile-time error (Invalid source file, or Source file not found).

In this way, string values within the source files are always valid Unicode strings independent on the web server configuration.

In case the string literal contains a byte sequence (denoted with \x[0-9A-Fa-f]{1,2} or \[0-7]{1,3}), the string value is represented with a byte array.

<?php
// assigns a string represented as a sequence of bytes
// [48 65 6c 6c 6f 20 0F]
$binaryvalue = "Hello \017";

String Operations#

Operations respect the Unicode semantic. All the library functions and operators are Unicode-safe by default, so they don't break a Unicode string. Operations working with bytes of the given string (e.g. base64_encode) will convert the given Unicode string to a byte sequence implicitly, using the current StringEncoding.

Concatenation#

The operator for the string concatenation (.) concatenates the given string values. If one of the operands is a Unicode string and the other is a byte sequence, the operands are concatenated as they are, resulting in a string value consisting of both - Unicode text followed by a byte sequence.

String length#

String length is counted as a number of elements within the string. The element can either be a UTF-16 character or a byte.

Array operator []#

Single elements within the string value can be accessed with the array operator ([]). Elements can either be changed or read.

If an element at a given position is a UTF-16 character, the result of the operation is a Unicode string with a single character. If the element is a single-byte, the result of the operation is a string with a single byte.

Output#

The string value can be output using standard functions (e.g. echo, print_r, etc.).

Unicode characters are encoded using the current output encoding. Single-byte elements are output as they are.

Regular expressions#

PCRE functions always convert input string values to a Unicode string value if they are a single-byte sequence.

Database#

Database drivers are Unicode-safe, as well. Any text value passed into or read from the database is a Unicode string. BLOB values remain as byte sequences.

Note, when reading string values from a database, ensure the CHARSET is set correctly according to the database configuration. The database driver is responsible for converting the values stored in the database to string values.

On the other hand, passing text values to the database is handled by PeachPie; Unicode values remain the same, byte-sequences are encoded to Unicode string values using StringEncoding configuration.

Conversions#

Any implicit conversions between a Unicode value and a byte sequence value respect the current StringEncoding.

To perform a conversion from Unicode to a byte-sequence explicitly, use the (binary) cast operator.

Configuration#

In short, all the encodings are UTF-8 by default. UTF-8 is the recommended encoding to be used for source files, content-encoding, HTML charset and database setup.

CodePage#

Property CodePage tells the compiler how to decode source files.

Output Encoding#

Web applications have an output encoding; it is responsible for encoding Unicode text to an underlying HTTP response stream. This option is set at run time by the web server.

Console applications always output text using UTF-8.

StringEncoding#

Internal encoding used for implicit conversions between Unicode characters and byte sequences. It is identical to Output Encoding. See Context for more details.

Limitations#

Since a string element can be both - a UTF-16 character or a byte - the string length (strlen) might become unpredictable.