libcamera: utils: Add string splitter utility function

Add a utils::split() function that splits a string for the purpose of
iterating over substrings. It returns an object of unspecified type that
can be used in range-based for loops.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
Signed-off-by: Kieran Bingham <kieran.bingham@ideasonboard.com>

Documentation/Doxyfile.in

@@ -880,6 +880,7 @@ EXCLUDE_SYMBOLS        = libcamera::BoundMethodArgs \
                          libcamera::BoundMethodStatic \
                          libcamera::SignalBase \
                          libcamera::*::Private \
+                         libcamera::*::details::* \
                          std::*
 
 # The EXAMPLE_PATH tag can be used to specify one or more files or directories

src/libcamera/include/utils.h

@@ -108,6 +108,40 @@ inline _hex hex<uint64_t>(uint64_t value, unsigned int width)
 
 size_t strlcpy(char *dst, const char *src, size_t size);
 
+namespace details {
+
+class StringSplitter
+{
+public:
+	StringSplitter(const std::string &str, const std::string &delim);
+
+	class iterator
+	{
+	public:
+		iterator(const StringSplitter *ss, std::string::size_type pos);
+
+		iterator &operator++();
+		std::string operator*() const;
+		bool operator!=(const iterator &other) const;
+
+	private:
+		const StringSplitter *ss_;
+		std::string::size_type pos_;
+		std::string::size_type next_;
+	};
+
+	iterator begin() const;
+	iterator end() const;
+
+private:
+	std::string str_;
+	std::string delim_;
+};
+
+} /* namespace details */
+
+details::StringSplitter split(const std::string &str, const std::string &delim);
+
 } /* namespace utils */
 
 } /* namespace libcamera */

src/libcamera/utils.cpp

@@ -199,6 +199,69 @@ size_t strlcpy(char *dst, const char *src, size_t size)
 	return strlen(src);
 }
 
+details::StringSplitter::StringSplitter(const std::string &str, const std::string &delim)
+	: str_(str), delim_(delim)
+{
+}
+
+details::StringSplitter::iterator::iterator(const details::StringSplitter *ss, std::string::size_type pos)
+	: ss_(ss), pos_(pos)
+{
+	next_ = ss_->str_.find(ss_->delim_, pos_);
+}
+
+details::StringSplitter::iterator &details::StringSplitter::iterator::operator++()
+{
+	pos_ = next_;
+	if (pos_ != std::string::npos) {
+		pos_ += ss_->delim_.length();
+		next_ = ss_->str_.find(ss_->delim_, pos_);
+	}
+
+	return *this;
+}
+
+std::string details::StringSplitter::iterator::operator*() const
+{
+	std::string::size_type count;
+	count = next_ != std::string::npos ? next_ - pos_ : next_;
+	return ss_->str_.substr(pos_, count);
+}
+
+bool details::StringSplitter::iterator::operator!=(const details::StringSplitter::iterator &other) const
+{
+	return pos_ != other.pos_;
+}
+
+details::StringSplitter::iterator details::StringSplitter::begin() const
+{
+	return iterator(this, 0);
+}
+
+details::StringSplitter::iterator details::StringSplitter::end() const
+{
+	return iterator(this, std::string::npos);
+}
+
+/**
+ * \fn split(const std::string &str, const std::string &delim)
+ * \brief Split a string based on a delimiter
+ * \param[in] str The string to split
+ * \param[in] delim The delimiter string
+ *
+ * This function splits the string \a str into substrings based on the
+ * delimiter \a delim. It returns an object of unspecified type that can be
+ * used in a range-based for loop and yields the substrings in sequence.
+ *
+ * \return An object that can be used in a range-based for loop to iterate over
+ * the substrings
+ */
+details::StringSplitter split(const std::string &str, const std::string &delim)
+{
+	/** \todo Try to avoid copies of str and delim */
+	return details::StringSplitter(str, delim);
+}
+
 } /* namespace utils */
 
 } /* namespace libcamera */