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Fixed-Length String

Current mainline string-related interfaces fall mainly into two groups:

  • LibXR::String<N>: fixed-capacity, value-semantics string objects
  • LibXR::RuntimeStringView<...>: runtime-built retained NUL-terminated string views

The first group fits small fixed-capacity string values. The second fits retained names or formatted results such as module names, topic names, and runtime-generated identifiers.

Feature Overview​

  • Fixed Length: The maximum length is specified via the template parameter MaxLength. Internally, it uses std::array<char, MaxLength+1> and is always null-terminated (\0).
  • Safe Operations: Most methods include boundary checks and assertions to prevent out-of-bounds access.
  • C-Style String Compatible: Supports construction from const char* or strings with a specified length. The Raw() method retrieves the underlying string.
  • Appending and Searching: Supports += for appending and Find() for substring search.
  • Full Comparison Operators: Supports ==, !=, <, >, <=, >=, including comparisons between different String<N> lengths.

Usage Example​

LibXR::String<32> s1("hello");
s1 += " world";
int idx = s1.Find("lo");  // returns 3
auto sub = s1.Substr<5>(6);  // extracts 5 characters starting from index 6
LibXR::RuntimeStringView<"camera_{}", unsigned int> name;
name.Reformat(7U);
// name.View() == "camera_7"

API Reference​

Constructors​

  • String() – Constructs an empty string.
  • String(const char* str) – Constructs from a C-style string.
  • String(const char* str, size_t len) – Constructs from a string with a specified length.

Basic Methods​

  • const char* Raw() const – Returns the underlying C-style string.
  • size_t Length() const – Returns the current string length.
  • void Clear() – Clears the string.
  • int Find(const char* str) const – Finds the position of a substring; returns -1 if not found.
  • template <unsigned int SubStrLength> String<SubStrLength> Substr(size_t pos) const – Extracts a substring starting at a given position.

Operators​

  • += – Appends a C-style string.
  • [] – Accesses characters by index (with boundary assertion).
  • Comparison operators – ==, !=, <, >, <=, >= are supported across String<N> of different lengths.

RuntimeStringView​

RuntimeStringView<Source, Args...> is the other public string capability in current mainline, defined in libxr_string.hpp.

Its main purpose is:

  • retaining one runtime-generated NUL-terminated text value
  • exposing it repeatedly through View() / CStr()
  • allocating capacity once from a compile-time upper bound on the first formatted rewrite, then reusing that same storage

Two construction paths​

  1. Plain text copy / concatenation path
LibXR::RuntimeStringView<> topic_name("camera/front");
LibXR::RuntimeStringView<> path("/dev/", "ttyUSB0");

This path accepts text-like inputs only. If you need numeric formatting, do not use the plain concatenation constructor.

  1. Formatted rewrite path
LibXR::RuntimeStringView<"camera_{}", unsigned int> name;
name.Reformat(7U);

LibXR::RuntimeStringView<"frame_%03u", unsigned int> frame;
frame.Reprintf(5U);
  • Reformat(...) uses brace-style formatting
  • Reprintf(...) uses printf-style formatting
  • the current implementation requires the rewrite call argument types to match the template-bound Args... exactly

Current mainline semantic boundaries​

  • Formatted RuntimeStringView arguments currently accept only value types whose capacity can be bounded statically; runtime string arguments are rejected and should use the plain RuntimeStringView<> concatenation path instead.
  • The current implementation does not free allocated storage in the object destructor. Its design target is a retained string view with one allocation and repeated reuse, not a short-lived auto-releasing text container.
  • Status() reports the result of the latest construction or rewrite; on failure, the visible text is cleared to an empty string.

Common access APIs​

  • std::string_view View() const
  • const char* CStr() const
  • size_t Size() const
  • bool Empty() const
  • ErrorCode Status() const

If you need deterministic capacity, value semantics, and ordinary object-style string lifetime, prefer String<N>. If you need a retained runtime name or a repeatedly rewritten formatted result, RuntimeStringView is the closer match to current mainline design.