c++ - Slow iterating over string using pointers -

-

i love see why 1 of following solution slower other. lets concider following code:

// create long string int x,y; bool b; char c[10000];  (x=0;x<10000;x++)     c[x]='a'; string s(c);

now want iterate on string , compare each character other. first solution completes task in 5 seconds:

for (y=0;y<100000;y++){ (x=0;x<10000;x++){     b = (s[x]=='a'); }}

and second in 21 seconds:

string::iterator begin = s.begin(); string::iterator end   = s.end(); string::iterator i;  (y=0;y<100000;y++){     (i=begin;i<end;i++){         b = (*i=='a'); }}

why second slower?

it having dereference pointer every time comparing iterator 'a', instead of comparing actual char value. negligible difference in cases, doing 1,000,000,000 iterations noticeable.


Popular posts from this blog

How to calculate SNR of signals in MATLAB? -

-
i've encountered simple, yet fundamental problem on calculating snr: there several signals : s1 = original , pure clean signal without noise. n1 = white gaussian noise going added s1. s2 = s1 + n1 (the noisy signal before performing noise-reduction algorithm) s3 = noise-reduced signal (after performing noise reduction algorithm) n2 = s3 - s1 (the amount of noise after performing noise-reduction algorithm) now want compare snr before , after performing noise-reduction algorithm. which signals should consider snr_before!? s1/n1 or s2/n1 ? which signals should consider snr_after!? s3/n1 or s3/n2 ? which commands or functions should use in matlab in order compute snr_before , snr_after? thanks billion putting time on helping me. what know calculating snr before : snrbeforenoise = mean( signal .^ 2 ) / mean( noise .^ 2 ); and snr after : residual_noise = signal - noise_reduced_signal; snr_after = mean( signal .^ 2 ) / mean( residual_noise .^ 2...
Read more

java - How to create Table using Apache PDFBox -

-
java - How to create Table using Apache PDFBox - we planning migrate our pdf generation utilities itext pdfbox (due licensing issues in itext). effort, able write , position text, draw lines etc. creating tables text embedded in table cells challenge, went through documentation, examples, google, stackoverflow couldn't find thing. wondering if pdfbox provides native back upwards creating tables embedded text. lastly resort utilize link https://github.com/eduardohl/paginated-pdfbox-table-sample thanks links provided tilman. using boxable api ( https://github.com/dhorions/boxable ) able create table wanted to. fyi wanted create table variable number of cells. illustration row 1 have 2 cells, row 2 have 5 cells , row 3 have 3 cells. able ease. followed example1.java in link mentioned above. java pdf pdfbox
Read more

c# - Attempting to upload to FTP: System.Net.WebException: System error -

-
i have api takes in xml , uploads files based on information in xml. uploads on schedule (also xml), , have tested surrounding , know works. i getting error 40% of time on first file attempt upload in each time cycle (time cycle = 45 minutes files, 30 minutes others). here code upload: try { loggerftp.log("uploading file: " + filename, false); // create request. ftpwebrequest request = (ftpwebrequest)webrequest.create(appsettingsftp.ftpurl + @"/" + filename); request.method = webrequestmethods.ftp.uploadfile; request.timeout = 6000000; //set 100 minutes //request.timeout = -1; //set infinite // add login credentials. request.credentials = new networkcredential(appsettingsftp.ftplogin, appsettingsftp.ftppassword); // grab file contents. streamreader sourcestream = new streamreader(appsettingsftp.uploadfiledirectory + filename); byte[] filecontents = encoding.utf8.getbytes(sourcestream.readtoend()); sourcest...
Read more