Qt wrongly thinks QImage is loaded properly - c++

Question

I am having an issue when trying to store a sequence of image data with Qt.
Here is a piece of code that shows the problem:
#include <vector>
#include <iostream>
#include <QImage>
...
const int nFrames = 1000;
std::vector<int> sizes(nFrames);
std::vector<uchar*> images(nFrames);
for (int k = 0; k < nFrames; k++)
{
QImage *img = new QImage("/.../sample.png");
uchar *data = img->bits();
sizes.at(k) = img->width() * img->height();
images.at(k) = data;
}
std::cout << "Data loaded \"successfully\"." << std::endl;
for (int k = 0; k < nFrames; k++)
{
std::cout << k << ": " << (int) (images.at(k)[0]) << std::endl;
}
In the first loop, the program loads QImage objects and puts the bitmaps in the images vector of pointers. In the second loop, we just read a pixel of each frame.
The problem is that the program proceeds through the first loop without complaining, even if the heap memory becomes full. As a result, I get a crash in the second loop, as shown by the output of the program:
Data loaded "successfully".
0: 128
1: 128
2: 128
...
192: 128
[crash before hitting 1000]
To reproduce the problem, you can use the grayscale image below, and you may need to change the value of nFrames, depending on how much memory you have.
My question is: How can I load the data in the first loop in a way that would allow me to detect if the memory becomes full? I don't necessarily need to keep the QImage objects in memory, but only the data of theimages vector.

Answer 1

Firs of all, the first loop has memory leak becouse of img objects are not deleted.
From Qt documentation:
uchar * QImage::bits()
Returns a pointer to the first pixel data. This
is equivalent to scanLine(0).
Note that QImage uses implicit data sharing. This function performs a
deep copy of the shared pixel data, thus ensuring that this QImage is
the only one using the current return value.
So you can safely delete img at and of loop.
....
images.at(k) = data;
delete img;
}
To detect if the memory becomes full you can check if operator new create QImage object like this:
QImage *img = new QImage("/.../sample.png");
if(!img) {
//out of memory
}

Answer 2

Partial answer:
The first loop can be replaced by the following:
for (int k = 0; k < nFrames; k++)
{
QImage *img = new QImage("/.../sample.png");
sizes.at(k) = img->width() * img->height();
uchar *data = new uchar[sizes.at(k)];
std::copy(img->bits(), img->bits() + sizes.at(k), data);
images.at(k) = data;
delete img;
}
This creates in images.at(k) a copy of the data that img->bits() points to. (Btw, this allows now to delete the QImage at the end of the first for loop.) An std::bad_alloc error in the loop if out of memory.
However, this is not good enough. I suspect possible issues when nFrames is set to a value such that the maximum memory taken by the program is close to the limit (or when another program frees memory while this is running). My concern is that I still have no guarantee that img.bits() returns a pointer to accurate data.