Reference question in C++ [modified]

[es1968]

Hi all, The following question: 1)string str1 = "a"; 2)string str2 = "b"; 3)string& refstr = str1; printf("\n str1: %s,", str1.c_str()); printf("\n str2: %s,", str2.c_str()); printf("\n refstr: %s,\n ", refstr.c_str()); 4)str1 = "aa"; printf("\n str1: %s,", str1.c_str()); printf("\n str2: %s,", str2.c_str()); printf("\n refstr: %s,\n ", refstr.c_str()); 5)refstr = str2; printf("\n str1: %s,", str1.c_str()); printf("\n str2: %s,", str2.c_str()); printf("\n refstr: %s,\n ", refstr.c_str()); 6)str2 = "bb"; printf("\n str1: %s,", str1.c_str()); printf("\n str2: %s,", str2.c_str()); printf("\n refstr: %s,\n ", refstr.c_str()); displays after each stage : 3) str1: a str2: b refstr: a 4) str1: aa str2: b refstr: aa 5) str1: b str2: b refstr: b 6) str1: b, str2: bb, refstr: b, May I get an accurate explantion why this is the display for each stage ? Why after stage 6 the display is not bb for all ? Thanks in advance, Eyal

modified on Sunday, October 11, 2009 7:32 AM

[CPallini]

es1968 wrote:

May I get an accurate explantion why this is the display for each stage ?

Yes, documentation [^] explains it all:

A reference holds the address of an object, but behaves syntactically like an object.

:)

If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler. -- Alfonso the Wise, 13th Century King of Castile.
This is going on my arrogant assumptions. You may have a superb reason why I'm completely wrong. -- Iain Clarke
[My articles]

[es1968]

Hi Pallini, Thanks for your the answer, but I want to understand why after stage 6, str1 and strref have not been changed after str2 changed to "bb" ? It's important for me to understand this, probably I miss something. Best, Eyal

[Rajesh R Subramanian]

es1968 wrote:

why after stage 6, str1 and strref have not been changed after str2 changed to "bb" ?

Because nothing is changing the values of str1 and strref. At stage 6, only the value of str2 is changed, so everything else remains the same. What are you not understanding?

It is a crappy thing, but it's life -^ Carlo Pallini

[CPallini]

Well, you know, roughly speaking, a reference is a sugar-added-pointer, so let's write your code again, this time using the real thing (BTW no need to say that Klingon developers don't use references, references are for sissies... :rolleyes: )

#include <string>
using namespace std;
#include <stdio.h>
void main()
{
// case 0
string str1 = "a";
string str2 = "b";
string * const pstr = &str1;//that's wath a reference really is

printf("\\ncase 0\\n str1: %s", str1.c\_str());
printf("\\n str2: %s", str2.c\_str());
printf("\\n refstr: %s\\n ", (\*pstr).c\_str());

// case 1
str1 = "aa";

printf("\\n case 1\\n str1: %s", str1.c\_str());
printf("\\n str2: %s", str2.c\_str());
printf("\\n refstr: %s\\n ", (\*pstr).c\_str());

// case 2
(\*pstr) = str2;

printf("\\n case 2\\n str1: %s", str1.c\_str());
printf("\\n str2: %s", str2.c\_str());
printf("\\n refstr: %s\\n ", (\*pstr).c\_str());

// case 3
str2 = "bb";

printf("\\n case 3\\n str1: %s", str1.c\_str());
printf("\\n str2: %s", str2.c\_str());
printf("\\n refstr: %s\\n ", (\*pstr).c\_str());

}

If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler. -- Alfonso the Wise, 13th Century King of Castile.
This is going on my arrogant assumptions. You may have a superb reason why I'm completely wrong. -- Iain Clarke
[My articles]

[es1968]

CPallini, Thanks a lot, Eyal

[es1968]

Rajesh, Thanks a lot, Eyal