How to get the pixels value of a png picture?

cocos2d-x
1

I am using the cocos2d-x v3.8.1.
I have tried this code to get the pixels value of a png picture,but got empty data.

Image * img = new Image();
img->initWithImageFile(mCurrentPictureDiffName);
unsigned char *data = img->getData();

Anybody can help me?

2

Image * img = new Image();
img->initWithImageFile(mCurrentPictureDiffName);
unsigned int *data = (unsigned int *)img->getData();

This code can get the pixels value.