false positive arrayIndexOutOfBounds when using pre-increment in member function call

[Yannick HOUDOT]

Hi Guys,

It looks like increment is evaluated twice ... do you know of this issue ?
change from post to pre-increment does not change anything.

if I change to
v[idx++].a =0;
then it's ok, but as soon as I called a member function, it goes awry.

void fct()
{
    struct _st_t{
        int a; 
        void set(size_t i) { a=i; }
    } v[4];

    int idx = 0;

    v[idx++].set(0);
    v[idx++].set(0);
    v[idx++].set(0);
    v[idx++].set(0);
}

logs:

$ cppcheck   test_incr_bound.cpp
Checking test_incr_bound.cpp ...
test_incr_bound.cpp:13:6: error: Array 'v[4]' accessed at index 5, which is out of bounds. [arrayIndexOutOfBounds]
    v[idx++].set(0);
     ^
test_incr_bound.cpp:9:15: note: Assignment 'idx=0', assigned value is 0
    int idx = 0;
              ^
test_incr_bound.cpp:11:7: note: idx is incremented', new value is 1
    v[idx++].set(0);
      ^
test_incr_bound.cpp:11:7: note: idx is incremented', new value is 2
    v[idx++].set(0);
      ^
test_incr_bound.cpp:12:7: note: idx is incremented', new value is 3
    v[idx++].set(0);
      ^
test_incr_bound.cpp:12:7: note: idx is incremented', new value is 4
    v[idx++].set(0);
      ^
test_incr_bound.cpp:13:7: note: idx is incremented', new value is 5
    v[idx++].set(0);
      ^
test_incr_bound.cpp:13:6: note: Array index out of bounds
    v[idx++].set(0);
     ^
test_incr_bound.cpp:14:6: error: Array 'v[4]' accessed at index 7, which is out of bounds. [arrayIndexOutOfBounds]
    v[idx++].set(0);
     ^
test_incr_bound.cpp:9:15: note: Assignment 'idx=0', assigned value is 0
    int idx = 0;
              ^
test_incr_bound.cpp:11:7: note: idx is incremented', new value is 1
    v[idx++].set(0);
      ^
test_incr_bound.cpp:11:7: note: idx is incremented', new value is 2
    v[idx++].set(0);
      ^
test_incr_bound.cpp:12:7: note: idx is incremented', new value is 3
    v[idx++].set(0);
      ^
test_incr_bound.cpp:12:7: note: idx is incremented', new value is 4
    v[idx++].set(0);
      ^
test_incr_bound.cpp:13:7: note: idx is incremented', new value is 5
    v[idx++].set(0);
      ^
test_incr_bound.cpp:13:7: note: idx is incremented', new value is 6
    v[idx++].set(0);
      ^
test_incr_bound.cpp:14:7: note: idx is incremented', new value is 7
    v[idx++].set(0);
      ^
test_incr_bound.cpp:14:6: note: Array index out of bounds
    v[idx++].set(0);
     ^

$ cppcheck --version
Cppcheck 2.13.0

$

[CHR]

Thanks for reporting, added here: https://trac.cppcheck.net/ticket/12731

[Yannick HOUDOT]

from the trac link, I thought the issue was corrected in 2.17.1 version... but It's still occurs.

Did I misunderstand or does the defect fall into limbo ?

(just asking !) Regards.

[CHR]

The ticket is still open, so unfortunately nothing has been fixed yet.