How can i skip over structures when writing in a binary file [c++] -


i have structure :

struct ticket {     bool isreserved; // seat resereved (true)     time_t soldon; //when has ticket been bought     double price; // price of ticket     ticket() {  isreserved = 0; price = 0; soldon = 0; } };

i have saved many times needed in binary file , read correctly. question when how can modify 1 structure when user wants buy ticket. example when wants buy 5th seat should go 5th structure , change data. here how try it.

std::cout<<"\nplease enter how many tickets purchase : \n"; {        if(number<0 || number > freeseats)         std::cerr<<"invalid input.try again: \n";     std::cin>>number;  }while(number<0 || number > freeseats);  int *t = new int[number];  for(int = 0; i<number; i++) {     int seat = 0;          {          std::cout<<"please enter seat "<<i<<" : ";         std::cin>>seat;          file.clear();         file.seekg(0,std::ios::beg);         for(int =1; <= seat; i++)         {             serializetickets(file,ticket);         }         if(ticket.isreserved == 1)             std::cout<<"the ticket has been reserved\n";     }while(ticket.isreserved == 1);      t[i] = seat; }  file.close();  schedule.serializetargetline(choice); std::ofstream myfile(ticketsfilename,std::ios::binary || std::ios::out);  for(int = 0; i<number; i++) {     time_t timer(0);     std::time(&timer);      myfile.seekp(+(t[i] - 1)*sizeof(ticket),std::ios::beg);      ticket.isreserved=1;     ticket.price = atof(schedule.getprice().c_str());     ticket.soldon = timer;      myfile.write(reinterpret_cast<char*> (&ticket),sizeof(ticket)); }  delete[] t; myfile.close();

if you're compiling gcc, encourage add -wall compiler flags maximum compiler assistance.

the problem appears not opening file writing:

std::ofstream myfile(ticketsfilename,std::ios::binary || std::ios::out);

when mean't

std::ios::binary | std::ios::out

or (std::ios::binary | std::ios::out)

if turn on full compiler warnings, tell you have boolean operation mean't have logical.

and, yes, should use pragma pack around structure. see http://msdn.microsoft.com/en-us/library/ms253935(v=vs.80).aspx , https://stackoverflow.com/a/9852860/257645

note, unless targetting older compilers, can as:

#pragma pack(push, 1) struct ... {     ... }; #pragma pack(pop)

(short version: tells compiler use in-memory representation of structure may less run-time performant create less environment-dependent footprint storage this)


Comments

Post a Comment

Popular posts from this blog

.htaccess - First slash is removed after domain when entering a webpage in the browser -

sometimes when hit address of webpage in browser, removes first slash after domain. examples: www.mywebsite.com/scripts/script_6.php -> trying load www.mywebsite.comscripts/script_6.php www.mywebsite.com/test.php -> trying load www.mywebsite.comtest.php after entering again, loads page. a .htaccess settings must wrong: rewritebase / errordocument 404 http://www.mywebsite.com/oops.php errordocument 401 /notallowed.php rewriteengine on # turn on rewriting engine #gzip <ifmodule mod_deflate.c> addoutputfilterbytype deflate text/text text/html text/plain text/xml text/css application/x- javascript application/javascript </ifmodule> #end gzip rewritecond %{http_host} ^mywebsite\.com rewriterule ^(.*)$ http://www.mywebsite.com$1 [r=permanent,l] directoryindex index6.php rewriterule ^termsofuse/?$ termsofuse.php [nc,l] # handle requests "adpolicy" rewriterule ^privacy-policy/?$ privacy-policy.php [nc,l] # handle requ...
Read more

Automatically create pages in phpfox -

i have array of information of places , wanna use them create multiple pages in phpfox site. first tried manually insert data in phpfox database (in tables of phpfox_pages , phpfox_pages_text ). the page shown in site when opening it's link, site says: the page looking cannot found. do know other tables should manipulate make work? or know plugin phpfox same? thanks, solved ( @purefan guide): "pages" has user if take @ phpfox_user table, you'll found out how fetch new records on that. there 2 ambiguous fields in table ( password & password_salt ). can use script create values fields: <?php function generaterandomstring() { $length = 164; $characters = '-_0123456789abcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyz'; $randomstring = ''; ($i = 0; $i < $length; $i++) { $randomstring .= $characters[rand(0, strlen($characters) - 1)]; } return $randomstring; } $ssalt = '';...
Read more

c# - Farseer ContactListener is not working -

i'm using farseer in xna project, have trouble contactlistener. created class contactlistener these 2 error messages , don't know how fix problems. the type or namespace name 'contactlistener' not found (are missing using directive or assembly reference?) the type or namespace name 'contactimpulse' not found (are missing using directive or assembly reference?) what wrong contactlistener class? class mycontactlistener: contactlistener { void begincontact(contact contact) { /* handle begin event */ } void endcontact(contact contact) { /* handle end event */ } void presolve(contact contact, ref manifold oldmanifold) { fixture fixturea = contact.fixturea; fixture fixtureb = contact.fixtureb; if (fixtureb.collisioncategories == category.cat10) { contact.enabled = false; } } void postsolve(contact contact, ref contactimpulse impulse) { /* handle post-solve event */ } }...
Read more