Re: free() allocated memory twice..
On Feb 12, 11:25 pm, Kai-Uwe Bux <jkherci...@gmx.net> wrote:
orm...@gmail.com wrote:
[about: free() allocated memory twice...]
.. is it an undefined behaviour??
Yes.
You would expect this code to this
code ti give a segmentation fault but it doesnt.. Why??
Because the behavior is _undefined_. That means, all your expectations ca=
n
be off.
Sample Code:
---------------
typedef struct {
char name[10];
int x;
} Employee;
int main()
{
// allocate and fill e1
Employee **e1 = (Employee**) malloc( 5 * sizeof(Employee*) );
for(i=0 ; i<5 ; ++i) {
e1[i] = (Employee*) malloc( sizeof(Employee) );
fillEmployee(e1[i]);
}
// make shallow copy
Employee **e2 = (Employee**) malloc( 5 * sizeof(Employee*) );
for(i=0 ; i<5 ; ++i) {
e2[i] = e1[i];
}
// free the copy
for(i=0 ; i<5 ; ++i) {
free(e2[i]);
}
free(e2);
e2 = NULL;
// free the original one
for(i=0 ; i<5 ; ++i) {
free(e1[i]);
}
free(e1);
e1 = NULL;
return 0;
}
BTW: asside from exhibiting undefined behavior, the code is not idiomatic=
..
You may want to consider the transition to std::string, std::vector, valu=
e
semantics, and if needed, new and delete.
Best
Kai-Uwe Bux
Thanks. Should I expect the same behavior if we used new and delete?
Also can we really make a similar shallow copying using std::vector's?
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