False positive: initialized array element reported as uninitialized after guarded loop write

[Rodri]

Hi, I found a false positive regarding the rule uninitvar.

In the following C++ program, cppcheck reports that array a is uninitialized when a[0] is returned. However, a[0] is always initialized before the return statement.

int main() {
  int a[2];
  int i;
  for (i = 0; i < 3; i++) {
    if (i >= 0 && i < 2)
      a[i] = 0;
  }
  return a[0];
}

The loop executes with i == 0, i == 1, and i == 2. For i == 0 and i == 1, the guard i >= 0 && i < 2 is true, so both a[0] and a[1] are assigned. The final iteration with i == 2 skips the write, but it does not make a[0] uninitialized.

Actual result

Cppcheck reports:

<error id="uninitvar" severity="warning" msg="Uninitialized variable: a" ...>
    <location line="8" column="10"/>
    <location line="5" column="16" info="Assuming condition is false"/>
    <symbol>a</symbol>
</error>

Cppcheck also reports knownConditionTrueFalse for i >= 0, which is expected and not part of this issue.

Expected result

Cppcheck should not report uninitvar for a at return a[0].

Verification

The issue was reproduced with:

cppcheck --output-format=xmlv2 --enable=all guarded_loop_array_init.cpp

Version: 2.21.0

[CHR]

Thanks for reporting, ticket is here: https://trac.cppcheck.net/ticket/14957