Bug in the linker

[johnny dude]

Hi,

I found a possible bug, ld does not produce an error message: "multiple
definitions" when it is a constructor defined in the structure declaration.

How to reproduce it:
I'm using the gcc:9.2.0 docker, created two files and the result listed
below:

***@44027fc60f45:/# cat a.cpp
#include <iostream>
struct A { int n; A(int n) : n(n + 10) {} };
int a(int n) { return A(n).n; }
extern int b(int n);
int main(int, char**) { std::clog << a(5) << ", " << b(5) << "\n"; }

***@44027fc60f45:/# cat b.cpp
#include <iostream>
struct A { int n; A(int n) : n(n + 100) {} };
int b(int n) { return A(n).n; }

***@44027fc60f45:/# g++ a.cpp b.cpp -o ab && ./ab
15, 15

***@44027fc60f45:/# g++ b.cpp a.cpp -o ba && ./ba
105, 105
***@44027fc60f45:/#

[Andreas Schwab]

Post by johnny dude
#include <iostream>
struct A { int n; A(int n) : n(n + 10) {} };
int a(int n) { return A(n).n; }
extern int b(int n);
int main(int, char**) { std::clog << a(5) << ", " << b(5) << "\n"; }
#include <iostream>
struct A { int n; A(int n) : n(n + 100) {} };
int b(int n) { return A(n).n; }

This violates basic.def.odr.

Andreas.

[johnny dude]

Thank you for the quick response.

I understand the violation.

In all other cases ld returns an error of: "multiple definitions".
Including the same code, with the constructor defined outside the struct
declaration.

I thought it might be an implementation detail.

Post by Andreas Schwab

Post by johnny dude
#include <iostream>
struct A { int n; A(int n) : n(n + 10) {} };
int a(int n) { return A(n).n; }
extern int b(int n);
int main(int, char**) { std::clog << a(5) << ", " << b(5) << "\n"; }
#include <iostream>
struct A { int n; A(int n) : n(n + 100) {} };
int b(int n) { return A(n).n; }

This violates basic.def.odr.
Andreas.
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