performance - C++ emplace_back parameters -


here piece of code in daily work. want ask if there difference between 2 cases, in terms of performance.

std::vector< std::pair<std::string, std::string> > avec;  // case 1 avec.emplace_back("hello", "bonjour");  // case 2 avec.emplace_back(std::pair("hello", "bonjour"));

following question:

what std::list these 2 cases?

emplace_back construct element in-place, argument passed in perfect-forwarded constructor element.

for 1st case, conceptually 1 step needed, i.e. appropriate constructor of std::pair invoked construct element directly in vector.

for 2nd case, 3 steps needed; (1) appropriate constructor invoked construct temporary std::pair, (2) element move constructed in vector in-place temporary std::pair, (3) temporary std::pair destroyed.


Comments

Post a Comment

Popular posts from this blog

Command prompt result in label. Python 2.7 -

i want put result(output) of shell command label. command works, label shows "0", however, in command prompt, result shown correctly, need showed in label. doing ubuntu. myg1 = button(root, text="rodyti informacija", command=lambda: gauti()) myg1.pack(side=bottom) def gauti(): imti = tekstas.get("1.0", "end-1c") info = subprocess.call("id '{imti}' ".format(imti=imti), shell=true) w = label(root, text= info) w.pack(side = bottom) subprocess.call() returns exit code of process created (in case 0 success). if want text output of process, should instead call subprocess.check_output() .
Read more

javascript - How do I use URL parameters to change link href on page? -

i change href value of link using url parameters. example: default <a id="dlink" href="link-1">link</a> but, when user goes https://url.com/?dlink=link-2 it swaps out link new link <a id="dlink" href="link-2">link</a> first need value url. if you're not using javascript framework can create function using jquery. please check get url parameter jquery or how query string values in js it. after that, element "a" id , set value there. $("#dlink").attr("href", hreffromparam);
Read more

amazon web services - AWS Route53 Trying To Get Site To Resolve To www -

so have domain nameservers pointed aws route 53. site hosted on ec2 instance , reachable resolves site.com, if input www.site.com. i'm curious how site resolve www.site.com. have under route53 domains hosted zone 2 additional record sets outside of ns , soa: a site.com ec2 elastic ip cname www.site.com ec2 public dns i can reach site using both site.com , www.site.com, resolve site.com. there way make if enter either, resolves www.site.com? at first, both should record set. a site.com ec2 elastic ip www.site.com ec2 elastic ip and need redirect setting in web server (nginx, apache, ..) following. (source: how redirect www non-www nginx on centos 7 ) redirect non-www www if want redirect users plain, non-www domain www domain, add server block: server { server_name example.com; return 301 $scheme://www.example.com$request_uri; } save , exit. configures nginx redirect requests "example.com" "www.example.com". not
Read more