CODEWITHSUNDEEP
c++
Ciaran Neely
Ciaran Neely

Reputation: 1

Why is cout outputting outputting backslashes and digits when I use it again?

I have this piece of code (something I threw together trying to isolate a weird error in a chess program I'm trying to write):

 #include <vector>
 #include <iostream>

class piece{
public:
 piece() : COLOUR('C'){}
 const char COLOUR;
};

std::vector<piece*> makeEmptyLine(){
 std::vector<piece*> emptyLine;
 piece null;
 emptyLine.push_back(&null);
 return emptyLine;
}

int main(){
 std::vector<piece*> emptyLine = makeEmptyLine();
 std::cout << (*emptyLine[0]).COLOUR;
 std::cout << (*emptyLine[0]).COLOUR;
 std::cout << (*emptyLine[0]).COLOUR;
 return 0;
}

And the output is C\367\367

The first std::cout << (*emptyLine[0]).COLOUR; always prints "C" (the expected result). But when it's used again, it outputs that backslash and three digits which change depending on how many times I use cout in the program.

Upvotes: 0

Views: 44

Answers (1)

Peter VARGA
Peter VARGA

Reputation: 5186

You have an undefined behaviour because you use the address of a local variable null which is destroyed once your function makeEmptyLine() returns.

Does your compiler complain when you try to compile it with the highest warning level?

Upvotes: 1

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