glibc detected *** free() invalid pointer

Question

Hi friends i am getting this error whwn i am running my code "glibc detected * free() invalid pointer" in my code i am creating 3 pointer and allocating memory to only one using new and deleting all the three pointer.

class test()
{
public : 
int a;
/..some functionality../

}; 

class second_test()
{
public : 
int b;
/..some functionality../
} 

  class third_test()
    {
    public : 
    int c;
    /..some functionality../
    } 




int main()
{
test *ptrtest;
second_test *psecond_test;
third_test*pthird_test;



ptrtest = new test;
/..Doing some functionality.../


delete ptrtest;
   delete psecond_test;
delete pthird_test;


}

and when i am running it is giving above error but surprisingly not al the time it is giving error 7 out nof 10 time it gives above error..please help me what exactly the problem. BECAUSE in c++ i think it is safe to delete NULL pointer.

Answer 1

second_test *psecond_test;

That does not point to a null pointer.

second_test *psecond_test = NULL; 

That does.

---

As an example, here's some code:

#include <cstdio>

int main() {
    struct x *ptr;
    printf("%p\n", ptr);
}

And when I run it, I get different addresses each time. (Although they could be the same, they could be zero, it's undefined what they are)

[10:36pm] ./foo
0x7fff6413205e
[10:36pm] ./foo
0x7fff6cff105e
[10:36pm] ./foo
0x7fff6890305e

---

Clang, for example, warns about this when I use -Wall .

[10:41pm] clang++ -Wall foo.cc
foo.cc:5:9: warning: variable 'ptr' is uninitialized when used here [-Wuninitialized]
        delete ptr;
               ^~~
foo.cc:4:10: note: initialize the variable 'ptr' to silence this warning
        int *ptr;
                ^
                 = NULL