c++11 - Defined function returning const reference to class member and copy of the variable -

-

i still little bit confused returning const reference. probably, has been discussed, let's have following code did not find same:

#include <vector> #include <iostream>  struct {     int datasize;     std::vector<char> data; };  class t { public:     t();     ~t();     const a& getdata(); private:     dataa; };  t::t() : dataa{1} { }  t::~t() { }  const a& t::getdata() {     return dataa; }  void main() {     t t;     datareceivedcpy = {};     datareceivedcpy = t.getdata();      const a& datareceivedref = t.getdata();     std::cout << datareceivedref.datasize << std::endl; }

what happens, when call

datareceivedcpy = t.getdata();

is correct? point of view, , copy of requested struct made, right?

on other hand,

const a& datareceivedref = t.getdata();

returns reference object member, correct, unless t object not destructed. right?

yes, understanding sounds correct.

datareceivedcpy = t.getdata();

calls copy assignment operator put copy of t.dataa in datareceivedcpy.

const a& datareceivedref = t.getdata();

does no copying , makes datareceivedref reference t.dataa. valid lifetime of t.


Comments

Post a Comment

Popular posts from this blog

Spring Boot + JPA + Hibernate: Unable to locate persister -

-
i trying work entity inside request method of spring boot application. entity in project , pom.xml has dependencies it. why error message?: org.hibernate.unknownentitytypeexception: unable locate persister: com.ric.bill.model.bs.par package com.ric.web; import java.util.concurrent.atomic.atomiclong; import javax.persistence.entitymanager; import javax.persistence.persistencecontext; import net.sf.ehcache.cachemanager; import net.sf.ehcache.management.cache; import net.sf.ehcache.management.cachestatistics; import org.hibernate.stat.statistics; import org.springframework.beans.factory.annotation.autowired; import org.springframework.boot.autoconfigure.domain.entityscan; import org.springframework.cache.annotation.enablecaching; import org.springframework.transaction.annotation.enabletransactionmanagement; import org.springframework.transaction.annotation.propagation; import org.springframework.transaction.annotation.transactional; import org.springframework.web.bind.annotati...
Read more

go - Golang: panic: runtime error: invalid memory address or nil pointer dereference using bufio.Scanner -

-
i implementing go program uses bufio.scanner , bufio.writer have packaged code follows package main import ( "fmt" "player/command" "strings" ) func main() { //enter code here. read input stdin. print output stdout commands.scanner.scan() { //scan new line , send comand variable check command exist or not input := strings.split(strings.trim(commands.scanner.text(), " "), " ") command := input[0] if command == "" { fmt.printf("$ %s:", commands.pwd) continue } if !commands.commands[command] { commands.throwerror("cannot recognize input.") } else { commands.execute(command, input[1:], nil) } fmt.printf("$ %s:", commands.pwd) } } i using init.go file in main package follows package main import ( "flag" "player/sourc...
Read more

c - double free or corruption (fasttop) -

-
this code reads null terminated string file (file containing null terminated strings & should provide index wanted string). error: *** error in `./main': double free or corruption (fasttop): 0x090a4a80 *** aborted code: char *tmp_realloc=null; char *sstring=null; int i=1; /*set file pointer point string*/ fseek(fh,index,seek_set); sstring=(char*)malloc(sizeof(char)); if(sstring == null) return null; tmp_realloc=sstring; while( (*(sstring+i-1)=(char)fgetc((file*)fh)) != 0x0 ) { /*reallocate more memory*/ tmp_realloc=(char*)realloc((char*)sstring,++i); /*if not same address copy old new & set old point new*/ if(tmp_realloc != sstring){ strcpy((char*)tmp_realloc,(char*)sstring); free(sstring); sstring=tmp_realloc; } } could tell me pointer causing issue (& reason) ? remove part /*if not same address copy old new & set old point new*/ if(tmp_realloc != sstring){ strc...
Read more