standard c_str() problem in C++

Question

4.00/5 (1 vote)

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I have craeted following kind of function in a class:

C++

void SetStr(string& s1, string& s2)
 {
 const char* s =(s1+s2).c_str();
 cout<<s<<endl;
 }

On calling it from main nothing is getting printed on console. While the following function works:

C++

void SetStr(string& s1, string& s2)
 {
 cout<<(s1+s2).c_str()<<endl;
 }

Can someone please tell me what is the problem.
Thank you.

Posted 21-Feb-12 18:54pm

Anitesh Kumar

Updated 21-Feb-12 19:38pm

Chandrasekharan P

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Comments

Chandrasekharan P 22-Feb-12 1:38am

Please do not repost your question and when you put the code please use pre tags.

jasonterry1 22-Feb-12 3:05am

umm... your code works for me...
(compiled gcc linux ubuntu)

5 solutions

Solution 5

It should be creating a temp string object in statement s1+s2, so why not put an s3 explicitly?

string st3 = s1+ s2;
const char* ch = st3.c_str();
cout<<ch;

btw, what's wrong with

just cout<<s1+s2 in the first place?

Posted 22-Feb-12 0:43am

Eytukan

Updated 22-Feb-12 8:50am

v2

Comments

CPallini 22-Feb-12 7:35am

Great Answer, my 5 (applause). BTW you should properly format your code. :-D

Emilio Garavaglia 22-Feb-12 14:51pm

Done!

CPallini 22-Feb-12 16:20pm

Così non vale: The youngster should format the code himself.

Solution 3

hi,
try this

C++

s1.append(s2);
cout << s1 <<endl;

Posted 21-Feb-12 22:08pm

Areff

Comments

CPallini 22-Feb-12 7:35am

Uhm, I see a side effect...

Solution 4

Thank you guys for replies... but my question was not "how can i print the concatinated string?"...It was "What is getting wrong in my code?". I got the answer from Emilio. Please refer that.

Posted 21-Feb-12 22:36pm

Anitesh Kumar

Solution 1

Try This :

C#

void SetStr(string& s1, string& s2)
{
    const char *s;
    strcpy(s,(s1+s2).c_str());
    cout<<s<<endl;
}

Posted 21-Feb-12 19:26pm

CRDave1988

Comments

tolw 22-Feb-12 4:52am

That's a terrible idea! You are copying a string to an unasigned pointer. No memory has been allocated so the code can have fatal results!

CPallini 22-Feb-12 7:36am

That's plainly wrong. Please remove it.

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Emilio Garavaglia · Accepted Answer · 2012-02-21T20:15:00

Solution 2

see here[^]

Posted 21-Feb-12 20:15pm

Emilio Garavaglia

Comments

Anitesh Kumar 22-Feb-12 4:07am

Thank you Emilio...