How to initialize c-strings array (no stl)

Question

I want to initialize array of c-strings with zero pointers in MSVC2010

// Foo.h
#pragma once
class Foo {
  int sz_;
  char **arr_; 
public:
  Foo();
  ~Foo();
  // ... some other functions
};

// Foo.cpp
#include "Foo.h"
#define INITIAL_SZ 20

Foo::Foo() : sz_(INITIAL_SZ) {
  // there I have to initialize arr_ (dynamic array and can be enlarged later)
  arr_ = (char **)calloc(INITIAL_SZ * sizeof (char *)); // ??? 
  // or maybe arr_ = new ...
}

How to correct initialize arr_? I was not allowed to use of STL, MFC, etc.

Just curious. Why no STL? And also what have you tried so far? Actually what you have there calloc() will initialize everything to zeros (NULL). — yasouser
– yasouser, Commented May 26, 2011 at 17:38

Alexander Gessler · Accepted Answer · 2011-05-26 17:39:25Z

5

arr = new char*[INITIAL_SZ](); will do - you can even put it in an initialization list.

answered May 26, 2011 at 17:39

Alexander Gessler

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Comments

Oliver Charlesworth · Accepted Answer · 2011-05-26 17:53:14Z

4

If you really want to avoid STL, etc., then why not:

arr_ = new char*[INITIAL_SZ]();

You could even put this in the initializer list.

Remember to invoke delete [] arr_ in your destructor. (As @Nawaz points out below, you should probably also follow the Rule of Three, and define a suitable copy-constructor and assignment operator as well.)

edited May 26, 2011 at 17:53

answered May 26, 2011 at 17:40

Oliver Charlesworth

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2 Comments

Alexander Gessler Over a year ago

I don't think it initializes them to zero, does it? (I'm not perfectly sure of the initialization rules, but I think the extra parentheses are needed)

Sarfaraz Nawaz Over a year ago

And also define copy-ctor and assignment operator : rule of three!

Matthieu M. · Accepted Answer · 2011-05-26 17:41:44Z

2

1. Build a proper string class

2. Build a proper array class

3. Use the array on strings

Happy chasing memory leaks, double frees and memory corruption.

answered May 26, 2011 at 17:41

Matthieu M.

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3 Comments

leetNightshade Over a year ago

Yes, except you didn't answer his question. "I was not allowed to use of STL, MFC, etc." Clearly he's following some specific guidelines, so your answer is completely unhelpful, if not a little stuck-up.

Matthieu M. Over a year ago

@leetNightshade: it's definitely stuck up, and meant as a taunt. However not using STL or MFC does not mean that you cannot create your own classes for memory management. My answer merely suggest to decompose the issue (String + Array) instead of trying to solve it all at once. And I know that the classes will be imperfect, experts get them wrong.

Greg Over a year ago

+1 a little extra work up front to avoid hours of painful string management and debugging by hand.

Himadri Choudhury · Accepted Answer · 2011-05-26 17:40:07Z

1

arr_ = (char **)calloc(INITIAL_SZ * sizeof (char *));

should be

arr_ = (char **)calloc(INITIAL_SZ, sizeof (char *));

answered May 26, 2011 at 17:40

Himadri Choudhury

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Comments

Jonathan Grynspan · Accepted Answer · 2011-05-26 17:40:33Z

1

The correct way is to redefine arr_ as std::vector<std::string> and to use vector::reserve() to hint at the number of strings you expect to have. Let C++ take care of the memory for you.

But if you must use raw C strings, you probably want:

arr_ = new char *[sz_];

answered May 26, 2011 at 17:40

Jonathan Grynspan

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