C++ alloc array of objects

Question

I've got this issue with allocation of an array of some objects that I need to initialize with some constructor. Let me show what I mean:

ofstream* out = new ofstream[10];

for(int i = 0; i < 10; i++){
    stringstream ss;
    ss << "file" << i << ".txt";
    string str(ss.str());
    char *fileName = (char*)str.c_str();
    out[i] = ofstream(fileName); //Now, this is wrong
}

And I need some help on the wrong marked line. How do I allocate each member of that array?

And thank you for not pointing me to other posts (I looked on a lot before posting)

out is susceptible to a memory leak. Remember to call delete[] on out. — user195488
– user195488, Commented Apr 12, 2011 at 20:05

Erik · Accepted Answer · 2011-04-12 20:02:02Z

5

Get rid of the fileName variable and use out[i].open(str.c_str()); - and remember to delete[] out;

answered Apr 12, 2011 at 20:02

Erik

91.8k13 gold badges203 silver badges192 bronze badges

Sign up to request clarification or add additional context in comments.

3 Comments

Iulius Curt Over a year ago

does delete[] also calls close() on each stream in my array?

Erik Over a year ago

@iuliux: delete[] will ensure the destructor of each stream is called - which closes it.

Iulius Curt Over a year ago

Cool. Then let your answer be the chosen one, though @Chris Kaminski also answered fine

Chris K · Accepted Answer · 2011-04-12 20:03:21Z

5

Here's the simplest solution to your problem.

out[i].open(fileName);

answered Apr 12, 2011 at 20:03

Chris K

12.4k8 gold badges41 silver badges65 bronze badges

Comments

Kiril Kirov · Accepted Answer · 2011-04-12 20:07:58Z

2

You could optimize this, with removing str and fileName:
out[ i ].open( ss.str().c_str() );

Also, I'd recommend you yo use std::vector not to carry about memory allocation and deallocation.
std::vector< std::ofstream >

answered Apr 12, 2011 at 20:07

Kiril Kirov

38.5k26 gold badges120 silver badges195 bronze badges

3 Comments

Iulius Curt Over a year ago

Well, I kind of read earlier why ss.str().c_str() doesn't work. The guys were saying that ss.str generates a temporary object.

Kiril Kirov Over a year ago

Huh? It's strange O.o I don't see anything wrong with this - yes, .str() returns temp object, but what? It's still "live" when opening the file(stream).

Kiril Kirov Over a year ago

I just ran this on Visual Studio 2010 and there are no even warnings, it works just fine :?

Konstantin Weitz · Accepted Answer · 2011-04-12 20:16:09Z

2

If you really need to call the constructor by the time you insert the element (maybe because your class doesn't have a default constructor), try placement new as described here http://www.parashift.com/c++-faq-lite/ctors.html#faq-10.5

answered Apr 12, 2011 at 20:16

Konstantin Weitz

6,5238 gold badges29 silver badges45 bronze badges

Collectives™ on Stack Overflow

C++ alloc array of objects

4 Answers 4

3 Comments

Comments

3 Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

4 Answers 4

3 Comments

Comments

3 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related