CODEWITHSUNDEEP
c++destructor
Ondra
Ondra

Reputation: 3180

Destructor on const char *

In my program, i have line like this:

    const char * str  = getStr();

Do i need to call destructor on str [] at the end of function to prevent memory leaks?

Upvotes: 9

Views: 7352

Answers (4)

Omnifarious
Omnifarious

Reputation: 56068

It all depends on what getStr() does. It may even be that you have to call free on the pointer if getStr() created it with malloc. It may be that getStr() is returning a pointer to a static area (not very thread safe, but it happens) or any number of other things.

Part of the contract and documentation for getStr() should be who owns the pointer it returns.

Here are some examples of possible getStr() functions...

In this case getStr() owns the pointer and you don't have to do anything to free it. OTOH, what's being pointed at may change the next time you call getStr() so you should probably make your own copy if you need to keep it around for any length of time:

const char *getStr()
{
    static char buf[30] = "Silly counter";

    buf[0] = buf[0] + 1;
    return buf;
}

In this case, you will eventually need to call free on the pointer returned:

const char *getStr()
{
    return strdup("Silly string");
}

In this case, you will need to call plain old delete on the pointer returned:

const char *getStr()
{
    return new char;
}

In this case, you will need to call delete [] on the pointer returned:

const char *getStr()
{
    return new char[50];
}

There are many other possibilities. As I stated previously, part of the contract for a function (which should appear in its documentation) is who owns the pointer returned and how that data pointed to must be disposed of if doing so is the caller's responsibility.

Upvotes: 3

6502
6502

Reputation: 114579

It depends on how getStr() has been designed. It could return a pointer to a string that is still owned by someone else (and in this case the answer is no) or it may return a pointer to and the caller becomes the owner (and in this case the answer is yes).

You should check the documentation of getStr to know.

If the ownership of the returned area is of the caller then probably in C++ returning an std::string would have been a much better idea.

Upvotes: 1

Steve Jessop
Steve Jessop

Reputation: 279365

Question does not contain enough information to tell, it depends what getStr() does. For example:

const char *getStr() {
    return "boo";
}

then you must not call delete.

const char *getStr() {
    return new char;
}

then you should call delete str; to avoid a memory leak (and must not call delete[]).

const char *getStr() {
    return new char[10];
}

then you should call delete[] str; to avoid a memory leak (and must not call delete).

const char *getStr() {
    return 0;
}

then it doesn't matter what you do, calling any kind of delete on str has no effect.

Ownership of resources, and how to release any resources owned, are part of the interface to a function, and should be documented at the same time as you document what the return value actually is.

Upvotes: 24

BrMcMullin
BrMcMullin

Reputation: 1261

It's a good idea to do so if it's going out of scope. I'd recommend also setting the pointer to null to ensure it isn't dangling:

delete[] str;
str = null;

Upvotes: 0

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