Error: illegal pointer to class object <histogram> 0x0 1401

I’ve got this error message and I wrote the part of my code below,

TH2D* fg2d_temp[8][4] = {0};

fg2d_temp[0][0] = (TH2D*)fin->Get(“fg2d_0_0”);

fg2d[0][0] = (TH2D*)fg2d_temp[0][0]->Clone();

I’ve checked that fg2d_temp is well written in infile ‘fin’.
It may be a silly question, but I have no idea what this message means and why this error message showed.
Could you give any suggestion?


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that means that you are using a null pointer (0x0).
You should check that the pointers coming from fg2d_temp that you use are not null (the simplest way is to print their values before you use them, you should see that one of the pointers you use is 0 or nullptr).


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Thanks, I printed my pointer and got 0.
I got null pointer because I made a typo when I get histogram from the file… I found it after following your suggestion. Thanks a lot!