New/Delete and Malloc/Free in C++ code

[Chris]

Hello all,

Does anyone know of or have experienced any problems with using new/delete
and malloc/free in the same same C++ code base? Of course, not using free()
on something you new'd.

Specially, I tend to deal with C-strings a lot and when I want to make a
copy I tend to use the strlen/new char[]/strncpy combination as in:

// s1 may be on the stack or heap it is unknown to the authour
// (i.e. returned for some library, etc.)

s1 = "Some string";

int n = strlen(s1);
char *s2 = new char[n+1];

strncpy(s2, s1, n);
s2[n] = '\0';

I would like to simplify this to simply:

s1 = "Some string"; // same conditions on s1 as above

char *s2 = strdup(s1);

However, the implementation of strdup() that I use uses malloc to duplicate
the string. Thus requiring me to use free() when I no longer want to use
s2.

So, could mixing new/delete and malloc/free in the same program cause
problems? I'm thinking issues with the heap, etc.

Thanks,

 

[Pete Becker]

// s1 may be on the stack or heap it is unknown to the authour
// (i.e. returned for some library, etc.)

s1 = "Some string";

int n = strlen(s1);
char *s2 = new char[n+1];

strncpy(s2, s1, n);
s2[n] = '\0';

strcpy will work just fine here.

I would like to simplify this to simply:

s1 = "Some string"; // same conditions on s1 as above

char *s2 = strdup(s1);

However, the implementation of strdup() that I use uses malloc to duplicate
the string. Thus requiring me to use free() when I no longer want to use
s2.

So, could mixing new/delete and malloc/free in the same program cause
problems? I'm thinking issues with the heap, etc.

No, there are no inherent problems.

 

[Victor Bazarov]

Does anyone know of or have experienced any problems with using
new/delete and malloc/free in the same same C++ code base? Of course,
not using free() on something you new'd.

Specially, I tend to deal with C-strings a lot and when I want to
make a copy I tend to use the strlen/new char[]/strncpy combination
as in:

// s1 may be on the stack or heap it is unknown to the authour
// (i.e. returned for some library, etc.)

s1 = "Some string";

int n = strlen(s1);
char *s2 = new char[n+1];

strncpy(s2, s1, n);
s2[n] = '\0';

I would like to simplify this to simply:

s1 = "Some string"; // same conditions on s1 as above

char *s2 = strdup(s1);

However, the implementation of strdup() that I use uses malloc to
duplicate the string. Thus requiring me to use free() when I no
longer want to use s2.

That's fine since the type is 'char'.

So, could mixing new/delete and malloc/free in the same program cause
problems? I'm thinking issues with the heap, etc.

Nope. Beyond the fact that 'strdup' is your own non-C++ function
which you use at your own risk, using new/delete (or new[]/delete[])
along with malloc/free is perfectly OK. Just don't use 'malloc'
for any non-POD types.

V

 

[Chris]

...

int n = strlen(s1);
char *s2 = new char[n+1];

strncpy(s2, s1, n);
s2[n] = '\0';

strcpy will work just fine here.

That's true. I tend to use strncpy() out of habit.

No, there are no inherent problems.

Thanks for the confirmation.