Operator overloading, implicit conversion, and false-positive "Returning pointer to local variable"

[Andrey Alekseenko]

Hi! The following code triggers a false-positive warning with a recent main (80c42fcaf305014ba7eaf4e234ee029a87819d44):

typedef float rvec[2];

class RVec {
public:
  RVec(float x, float y) : x_{x, y} {}
  RVec(const rvec x) : x_{x[0], x[1]} {}
  float operator[](int i) const { return x_[i]; }
  RVec operator+(const RVec &right) const {
    return {x_[0] + right[0], x_[1] + right[1]};
  }
  rvec x_;
};

int main() {
  auto foo = [](RVec x) {
    rvec dx;
    dx[0] = dx[1] = 1.F;
    return x + dx;
  };
}

Checking test_add.cpp ...
test_add.cpp:18:14: error: Returning pointer to local variable 'dx' that will be invalid when returning. [returnDanglingLifetime]
    return x + dx;
             ^
test_add.cpp:18:16: note: Array decayed to pointer here.
    return x + dx;
               ^
test_add.cpp:16:10: note: Variable created here.
    rvec dx;
         ^
test_add.cpp:18:14: note: Returning pointer to local variable 'dx' that will be invalid when returning.
    return x + dx;
             ^

We are not doing any pointer arithmetics here, since dx is converted to RVec, and then the overloaded operator+ is used.

[CHR]

Thanks for reporting, ticket is here: https://trac.cppcheck.net/ticket/11829

[Andrey Alekseenko]

Thanks!