[cfe-users] Strange null dereference error

[Morrell, Michael]

With the following code:

=================================
#include <stdlib.h>

extern bool x, y, z;

void foo(uint16_t *p)
{
    uint16_t *px = NULL, *py = NULL, *pz = NULL;

    if (x) {
        px = p;
        p += 32;
    }

    if (y) {
        py = p;
        p += 32;
    }

    if (z)
        pz = p;

    if (px != NULL)
        px[0] = 0;
    if (py != NULL)
        py[0] = 0;
    if (pz != NULL)
        pz[0] = 0;
=================================

Running:

  checker-275/libexec/c++-analyzer -c foo.cpp gives:


foo.cpp:25:15: warning: Array access (from variable 'py') results in a null pointer dereference
        py[0] = 0;
        ~~    ^
foo.cpp:27:15: warning: Array access (from variable 'pz') results in a null pointer dereference
        pz[0] = 0;
        ~~    ^
2 warnings generated.

All variables are checked for NULL right before the deference.  It is OK with "px", but not "py" or "pz".

As an aside, running "scan-build c++ -c foo.cpp" says there are no bugs.   I don't know why that would be different.

Should I just file a bug for this?

  Michael