[libcamera-devel] [PATCH 1/3] libcamera: utils: Add string splitter utility function

[Laurent Pinchart]

Hi Kieran,

On Thu, Feb 13, 2020 at 04:10:10PM +0000, Kieran Bingham wrote:
> On 13/02/2020 13:36, Laurent Pinchart wrote:
> > On Thu, Feb 13, 2020 at 01:24:27PM +0000, Kieran Bingham wrote:
> >> On 13/02/2020 13:09, Kieran Bingham wrote:
> >>> From: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
> >>>
> >>> 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 at ideasonboard.com>
> >>
> >> This is really helpful, thanks
> >>
> >> Reviewed-by: Kieran Bingham <kieran.bingham at ideasonboard.com>
> >>
> >>> ---
> >>>  Documentation/Doxyfile.in     |  1 +
> >>>  src/libcamera/include/utils.h | 34 +++++++++++++++++++
> >>>  src/libcamera/utils.cpp       | 62 +++++++++++++++++++++++++++++++++++
> >>>  3 files changed, 97 insertions(+)
> >>>
> >>> diff --git a/Documentation/Doxyfile.in b/Documentation/Doxyfile.in
> >>> index 1c46b04b3f7e..beeaf6d3cf48 100644
> >>> --- a/Documentation/Doxyfile.in
> >>> +++ b/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
> >>> diff --git a/src/libcamera/include/utils.h b/src/libcamera/include/utils.h
> >>> index e467eb21c518..080ea6614de0 100644
> >>> --- a/src/libcamera/include/utils.h
> >>> +++ b/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_;
> > 
> > Note that I would really like if we could store references to str and
> > delim here, but my attempt to do so resulted in problems, I believe due
> > to the values passed to the StringSplitter constructor being
> > temporaries. I don't know if there's a good way to solve that.
> 
> This isn't used in any hot-path, so I'm not worried for now.
> 
> If it comes up in the future it can be investigated then.
> 
> Would you like to add a todo: ? or not worth it?

It's always good to keep todos in mind :-) Please see below.

> >>> +};
> >>> +
> >>> +} /* namespace details */
> >>> +
> >>> +details::StringSplitter split(const std::string &str, const std::string &delim);
> >>> +
> >>>  } /* namespace utils */
> >>>  
> >>>  } /* namespace libcamera */
> >>> diff --git a/src/libcamera/utils.cpp b/src/libcamera/utils.cpp
> >>> index 4beffdab5eb6..fe027c0b009c 100644
> >>> --- a/src/libcamera/utils.cpp
> >>> +++ b/src/libcamera/utils.cpp
> >>> @@ -199,6 +199,68 @@ 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 */

-- 
Regards,

Laurent Pinchart