Error C4703 potentially uninitialized local pointer variable 'y' used

Question

I'm getting an error potentially uninitialized local pointer variable 'y' used & potentially uninitialized local pointer variable 'z' used, in the code provided below. Please help me with the solution?

UINT8* x = new UINT8[512];
if (!x) goto clean;

//UINT32* y = NULL;
UINT32* y = new UINT32[4];
if (!y) goto clean;

//char* z = NULL;
char* z = new char[512];
if (!z) goto clean;

{.... Some Code....}

clean:

    if (x) delete[] x;
    if (y) delete[] y;
    if (z) delete[] z;

Did you come from 33 years ago? is the story repeating again? — Blasco, Feb 05 '18 at 09:43
if any but the last `goto` triggers you `delete[]` an unitialized pointer. If thats fine for you (i hope not) then you can ignore the warning, otherwise use RAII instead of `goto` — 463035818_is_not_an_ai, Feb 05 '18 at 09:47
actually this is the best example for the evilness of `goto` I encountered so far. I wasnt even aware that `goto` enables to jump over a declaration but still use the variable later — 463035818_is_not_an_ai, Feb 05 '18 at 09:49

songyuanyao · Accepted Answer · 2018-02-05T09:53:16.310

Move all the initializations to the beginning. Otherwise with if (!x) goto clean; and jumps to clean, y and z are still not initialized.

UINT8* x = NULL;
UINT32* y = NULL;
char* z = NULL;

x = new UINT8[512];
if (!x) goto clean;

y = new UINT32[4];
if (!y) goto clean;

z = new char[512];
if (!z) goto clean;

PS: As others pointed, in modern C++, raw pointers (and new and delete), and goto should not be used in general. You might want to refer to The Definitive C++ Book Guide and List.

score 3 · Answer 2 · answered Feb 05 '18 at 10:01

3

For reference, here's the 21st century version:

std::vector<std::uint8_t> x {512};
std::vector<std::uint32_t> y {4};
std::vector<char> z {512}; // Or std::string

Notice the lack of clean:. This is intentional. The compiler inserts clean-up code.

answered Feb 05 '18 at 10:01

MSalters

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And `std::array` for 2011 version. – songyuanyao Feb 05 '18 at 10:03
2

@songyuanyao: I'm converting like for like. Presumably the old code had good reason to put these containers on the heap, so I kept that. The whole point of RAII is that you can get the semantics of local variables even with heap allocation. – MSalters Feb 05 '18 at 10:12

score 2 · Answer 3 · answered Feb 05 '18 at 09:42

2

If you jump to goto from here:

if (!x) goto clean;

Then y and z would have never been initialized here:

if (x) delete[] x;
if (y) delete[] y;
if (z) delete[] z;

The real answer to this question is: do not use goto, especially in C++. Use std::unique_ptr instead to manage your memory automatically.

answered Feb 05 '18 at 09:42

Vittorio Romeo

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Can you also provide me an example for using std::unique_ptr, I'm new to coding! – user9059547 Feb 05 '18 at 14:37

Error C4703 potentially uninitialized local pointer variable 'y' used

3 Answers3