String processing
Basic string operations
There exists a small set of string-manipulation operations as global functions in the Genode namespace.
repos/base/include/util/string.h
To cover the common case of embedding a string buffer as a member variable in a class, there exists the String class template, which alleviates the need for C-style arrays in such situations.
The String constructor takes any number of arguments, which will appear concatenated in the constructed String. Each argument must be printable as explained in Section Diagnostic output.
There exist a number of printable helper classes that cover typical use cases for producing formatted text output.
- Number_of_bytes
-
wraps an integer value and produces an output suffixed with K, M, or G whenever the value is a multiple of a kilobyte, megabyte, or gigabyte.
- Cstring
-
wraps a plain C character array to make it printable. There exist two constructors. The constructor with one argument expects a null-terminated character array. The other constructor takes the number of to-be-printed characters as arguments.
- Hex
-
wraps an integer value and produces hexadecimal output.
- Char
-
produces a character corresponding to the ASCII value the wrapped integer argument.
To improve safety in situations that require raw byte-wise access of memory, the two utilities Byte_range_ptr and Const_byte_range_ptr hold a pointer together with a size limit in bytes. They should be used instead of traditional C-style pairs of pointer and size arguments to equip each pointer with its legitimate range of access. Note that the utilities are meant for transient arguments only. They are deliberately not copyable to prevent the accidental storing of the embedded pointer values.
Tokenizing
For parsing structured text such as argument strings or XML, simple tokenizing support is provided via the Token class.
Diagnostic output
To enable components to produce diagnostic output like errors, warnings, and log messages, Genode offers a simple Output interface for sequentially writing single characters or character sequences.
Functions for generating output for different types are named print and take an Output & as first argument. The second argument is a const & to the value to print. Overloads of the print function for commonly used basic types are provided. Furthermore, there is a function template that is used if none of the type-specific overloads match. This function template expects the argument to be an object with a print method. In contrast to a plain print function overload, such a method is able to incorporate private state into the output.
repos/base/include/base/output.h
The component's execution environment provides an implementation of the Output interface that targets a LOG session. This output back end is offered to the component in the form of the log, warning, error, and trace functions that accept an arbitrary number of arguments that are printed in a concatenated fashion. Each message is implicitly finalized with a newline character.
Unicode handling
The string-handling utilities described in Section Basic string operations operate on ASCII-encoded character strings where each character is encoded as one byte. It goes without saying that ASCII is unsuitable for user-facing components that are ultimately expected to support the display of international characters. The Utf8_ptr utility accommodates such components with an easy way to extract a sequence of Unicode codepoints from an UTF-8-encoded string.