Strings are sequences of characters represented by c8, c16 and c32, terminated by a null terminator (\0). Luna SDK provides various string types and libraries, they will be discussed in this section.

String types

#include <Luna/Runtime/String.hpp> // For String, String16 and String32.
#include <Luna/Runtime/Name.hpp> // For Name.

Luna SDK provides two kinds of string types: String and Name.

The String type is a sequence of c8 characters ended with \0. We designed String as a replacement of std::string in Luna SDK, so most methods used for std::string should work find with our String type. Besides the String type, we also have String16 and String32 as replacements for std::u16string and std::u32string that holds character sequences of c16 and c32 types.

The Name type represents one immutable c8 string that is usually used as an identifier. We implemented a global name registry in Luna SDK so that every unique name will have only one data copy in the registry, and all Name objects with the same string data refers to that copy, thus can be compared for equality quickly. The name string data is reference counted, and will be freed when the last Name object that refers to the data is destructed. Strings stored in Name cannot be changed, if the user assigns Name with another string, the Name object will refer to another string data entry, remaining the original string entry unchanged.

Name and String can be converted to each other implicitly. There is no enforced encoding format for string types, but most text processing APIs in Luna SDK expects UTF-8 encoded strings for String and Name types.

String utility library

#include <Luna/Runtime/StringUtils.hpp>

The string utility library provides functions for processing characters and strings. Luna SDK imports the following string and character processing functions from C standard library that can be used directly in Luna SDK:

  1. strncpy
  2. strcat
  3. strncat
  4. strxfrm
  5. strncmp
  6. strcoll
  7. strchr
  8. strrchr
  9. strspn
  10. strpbrk
  11. strstr
  12. strtok
  13. isalnum
  14. isalpha
  15. islower
  16. isupper
  17. tolower
  18. toupper
  19. isdigit
  20. isxdigit
  21. iscntrl
  22. isgraph
  23. isspace
  24. isblank
  25. isprint
  26. ispunct

strlen, strcpy and strcmp are compatible to C standard library, but are extended by Luna SDK so they handles all character types. strcmp_prefix checks whether one string is the prefix string of another string, and returns 0 if is. strtoi64, strtou64 and strtof64 interprets one number value presented the by string, and returns the value.

Unicode encoding library

#include <Luna/Runtime/UTF8.hpp>

Unicode is a text encoding standard that is widely used in modern computers, programs and websites. Luna SDK comes with a built-in Unicode library for processing strings encoded in commonly-used Unicode formats, including UTF-8, UTF-16 (LE and GE) and UTF-32.

Luna SDK uses 32-bit character type (c32) to represent one Unicode character, the value of the character object represents the codepoint of the character in Unicode character table. One Unicode character can be encoded to 1 c32 character in UTF-32, 1 to 2 c16 characters in UTF-16, and 1 to 6 c8 characters in UTF-8.

By definition, one Unicode character represented by c32 differs from one Unicode character encoded using UTF-32 (the first bit of one UTF-32 character must be 0, so only 2^32 Unicode codepoints can be represented in UTF-32). But in practice, all existing Unicode characters can be converted to their UTF-32 representation without any modification, so we do not differ one Unicode character from one UTF-32 character in this manual.

utf8_charspan and utf16_charspan take one Unicode character, and return the number of c8 or c16 characters required to represent that character in UTF-8 or UTF-16 encoding. utf8_charlen and utf16_charlen take the first c8 or c16 character of one UTF-8 or UTF-16 encoded Unicode character, and return the number of bytes used for that character. These functions can be used to measure the size of one UTF-32 character in UTF-8 and UTF-16 encoding.

utf8_strlen and utf16_strlen calculate the number of Unicode characters contained by a UTF-8 or UTF-16 encoded string, utf8_index and utf16_index return the index of the first c8 or c16 character of the nth Unicode character in a UTF-8 or UTF-16 ebcided string. These functions can be used to calculate the length of Unicode-encoded strings.

utf8_encode_char and utf16_encode_char encode one Unicode character into multiple c8 or c16 characters using UTF-8 or UTF-16 encoding, write the encoded characters to the user-provided buffer, and return the number of characters written. utf8_decode_char and utf16_decode_char, on the other side, read multiple c8 or c16 characters from the user-provided buffer, and returns the Unicode character represented by these characters.

utf16_to_utf8 converts a UTF-8 encoded string to a UTF-16 encoded string, and utf8_to_utf16 converts a UTF-16 encoded string to a UTF-8 encoded string. Both functions write result strings in a user-provided buffer, utf16_to_utf8_len and utf8_to_utf16_len can be used to calculate the minimum size (measured in number of c8 or c16 characters, not including the null terminator) required for the buffer to hold the result string.

Base64 encoding library

#include <Luna/Runtime/Base64.hpp>

Base64 is an encoding format that represents arbitrary binary data using 64 printable characters, plus one character (=) for paddings. It is useful to store binary data in a text-based file. Luna SDK comes with a built-in Base64 library for encoding and decoding binary data using Base64.

base64_encode encodes the binary data in the user-provided source buffer to a Base64 encoded string, and writes the string to the user-provided destination buffer. To determine the size of the destination buffer required, call base64_get_encoded_size with the size of the row binary data.

base64_decode decodes the Base64 string in the user-provided source buffer to original binary data, and writes the binary data to the user-provided destination buffer. To determine the size of the destination buffer required, call base64_get_decoded_size with the size of the Base64 string, excluding the null terminator.