如何在 C++ 中初始化指针数组

Question

I used valgrind to test my code, and found out that the problem might be with the way I initialized the pointer array. But I am not sure where the problem is.

Here's the error:

Conditional jump or move depends on uninitialised value(s)

==7846==    at 0x41065A: Scene::drawscene() const (scene.cpp:142)

==7846==    by 0x4111C3: main (testscene.cpp:48)

==7846==  Uninitialised value was created by a heap allocation

==7846==    at 0x4C29F90: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)

==7846==    by 0x50C1829: operator new(unsigned long) (in /usr/lib/libc++abi.so.1.0)

==7846==    by 0x40FBE8: Scene::copy(Scene const&) (scene.cpp:45)

==7846==    by 0x40FB7C: Scene::Scene(Scene const&) (scene.cpp:22)

==7846==    by 0x41108E: main (testscene.cpp:41)

==7846== 
==7846== Conditional jump or move depends on uninitialised value(s)

==7846==    at 0x4107AB: Scene::drawscene() const (scene.cpp:149)

==7846==    by 0x4111C3: main (testscene.cpp:48)

==7846==  Uninitialised value was created by a heap allocation

==7846==    at 0x4C29F90: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)

==7846==    by 0x50C1829: operator new(unsigned long) (in /usr/lib/libc++abi.so.1.0)
==7846==    by 0x40FBE8: Scene::copy(Scene const&) (scene.cpp:45)
==7846==    by 0x40FB7C: Scene::Scene(Scene const&) (scene.cpp:22)
==7846==    by 0x41108E: main (testscene.cpp:41)

And the way I initial the array is below:

 Image** image;
    int** sequence;
    images = new Image*[max];
    sequence = new int*[max];

Answer 1

To my eye, this makes little sense:

int** sequence;
sequence = new int*[max];

I omit images here, because this integer pointer array indicates what may be the flaw in your thinking, reflected in the images array as well.

Why would anyone make an array of integer pointers? On most hardware, the integers are the same size as the pointers, and where are the actual integers they would point to?

Is it possible you really mean

int* sequence;
sequence = new int[max];

An array of integers, which could now actually store numbers?

Perhaps that's the same problem with your images array, because you are forming an array of image pointers. Now, an image, whatever that actually is, may indeed be more deserving of an array of pointers to images - that is actually a more common concept than an array of pointers to integers.

So, the question now becomes, if you have an array of image pointers, where are the images you are pointing to? Are you, sometime later, doing:

images[ n ] = new image;

Or something to that effect? That would point the entry n to an image, at least. Or, do you really mean to create an array of images, as above I suggested an array of integers:

Image* image;
images = new Image[max];

Answer 2

I think that what you are trying to do is initialize a dynamic 2D array of ints and of the type Image. Here is a working example for initializing the sequences variable:

int** sequences = new int*[max];
    for(int i = 0; i < max; ++i)
        sequences [i] = new int[max];

This is assuming that your 2D array is of the NxN .

A 2D array is just a pointer to an array of pointers so what the code does, it first initializes the pointer to the array of pointers:

int** sequences = new int*[max];

But now you have an array of pointers pointing to nowhere, so you have to also initialize them:

for(int i = 0; i < max; ++i)
    sequences [i] = new int[max];

I'll leave it to you to do the same for the images variable.