String Algorithms

std::string has a bunch of member functions that are essentially algorithms hanging off of a string type for no reason. Instead of repeating this with the types in the text layer, Boost.Text instead provides these algorithms as free functions, like all the other C++ algorithms. Unlike all the other C++ algorithms, the Boost.Text string algorithms work with code_point_ranges, grapheme_ranges, and even pointers to null-terminated strings, in all the permutations you might need. You can use ranges, just like with the algorithms in std::ranges:

assert(boost::text::starts_with(U"here", U"her")); // Like std::ranges::starts_with().

You can use any range that models utf_range_like or grapheme_range. You can also compare a range to a C-style null-terminated string pointer, even if the C-style string is in a different UTF format:

char const * her = "her";
assert(boost::text::starts_with(U"here", her));

And of course, the text-layer types are supported:

boost::text::rope here = "here";
boost::text::text_view her = "her";
assert(boost::text::starts_with(here, her));

	Tip
	If you like using the Boost.StringAlgo library, the text layer types work with those as well. Just be sure to use the code point iterators of your favorite text-layer type; Boost.StringAlgo doesn't know anything about graphemes.

See string_algorithm.hpp for a list of all the algorithms.

Utilities

There are a lot of small utility functions scattered throughout the Boost.Text headers. My philosophy is that if I have to write a function f() to implement a major feature, and f() seems like it might be useful to someone, somewhere, ever, I'm going to keep f() publicly available, rather than putting in a detail namespace. I'm not going to list all the available functions, but here are some pointers to where you can find them:

- transcode_iterator.hpp contains a variety of utility functions that give info on code points and UTF-8 code units. For instance, it contains replacement_character(), which just gives you the value of the Unicode replacement character, and scalar_value(), which tells you if a given unsigned int is in the range of Unicode scalar values.

- There are a couple of overloads of to_string() that can be used to construct a std::string from a range of code points.

- General-purpose algorithms can be found in algorithm.hpp. These are essentially back-ports of algorithms that are available anywhere from C++26 on back to C++98. They differ from the ones in std in that they are sentinel-friendly, and some have different names, because they predate the ones in the standard.

- There are numerous foo_prop() functions, where foo is word, line, etc. These give the text segmentation- or algorithm-specific property for any code point. See word_prop() in word_break.hpp for an example.