Get Segfault when setting branch address in different functions

[Crisps]

Dear experts

I passed a TTree to another function and set branch addresses there for 3 variables a b c, and then I set the branch address in the main function again for 2 variables a b, then set fault occurs when I try to GetEntry(). Why?

int main(){
//omit
int[3] a;
int[3] b;

TTree* t = (TTree*)f->Get("t");

DoIt(t);

t->SetBranchAddress("a", &a);
t->SetBranchAddress("b", &b);

t->GetEntry(0); //Segfault here
//omit
}

void DoIt(TTree* t){
int[3] a;
int[3] b;
int[3] c;
t->SetBranchAddress("a", &a);
t->SetBranchAddress("b", &b);
t->SetBranchAddress("c", &c);
//omit
}

[Danilo]

Hi,

The variables the addresses of which you are using are allocated on the stack of the function you mention. When returning these addresses become invalid.

Best,
Danilo

[Crisps]

Thank you, but I’m not using them in the main function, and I reset the address for a and b, not for c because I won’t use it, but still got segfault.

[dastudillo]

Reset the branch addresses just before leaving DoIt:

//...
t->SetBranchAddress("a", &a);
t->SetBranchAddress("b", &b);
t->SetBranchAddress("c", &c);
//...
t->ResetBranchAddresses();
}

[Danilo]

Hi,

Correct. However, their address is still saved in the TTree branches. A way to avoid that, is indeed what @dastudillo proposed.

Cheers,
D