Question

I’m learning C++ right now using Bruce Eckel’s “Thinking in C++” and I’m in the early chapters. I’ve got a C and Java background. Right now I’ve got the following problem: When I compile the sources below with

g++ A.cpp B.cpp bmain.cpp

, the program outputs a “1” (correctly) and then a segfault. When I compile with

g++ -g A.cpp B.cpp bmain.cpp

, the exact same program produces a 1 and NO segfault! I’ve got to say I find this astonishing. Could someone point out what I do wrong? My OS is “Linux 2.6.35-30-generic #54-Ubuntu x86_64”, my g++ is version “g++ (Ubuntu/Linaro 4.4.4-14ubuntu5) 4.4.5”.

EDIT: Just because this seems to be an important source of the error, thanks @Evan Teran: The A constructor in the B struct never gets called! I’ve put a “cout << “blah” << endl;” inside and it doesn’t print anything

EDIT: I’ve included the “return 0” at the end of main now, but that doesn’t help.

A.h:

#ifndef A_H
#define A_H

#include <string>

class A {
public:
        int i;
        std::string str;
        void print();
        A();
};

#endif

A.cpp:

#include "A.h"
#include <iostream>
#include <string>

using namespace std;

void A::print() {
        cout << str << " " << i << endl;
}

A::A() {
        str = "initstr";
    i = 0;
}

B.h:

#ifndef B_H
#define B_H

#include "A.h"

class B {
private:
        int counter;
public:
        A a;
        B();
        void increase();
        int read();
};

#endif

B.cpp:

#include "B.h"

using namespace std;

B::B() {
        counter = 0;
}

void B::increase() {
        ++counter;
}

int B::read() {
        return counter;
}

bmain.cpp:

#include <iostream>
#include "B.h"

using namespace std;

int main(int argc, char **argv) {
        B b;
        b.increase();
        cout << b.read() << endl;
        return 0;
}

EDIT: I’ve installed g++ from the packages. My Ubuntu is also very standard.

This is what I get when I call
gdb a.out core

warning: Can't read pathname for load map: Eingabe-/Ausgabefehler.
Reading symbols from /usr/lib/libstdc++.so.6...(no debugging symbols found)...done.
Loaded symbols for /usr/lib/libstdc++.so.6
Reading symbols from /lib/libm.so.6...Reading symbols from /usr/lib/debug/lib/libm-2.12.1.so...done.
done.
Loaded symbols for /lib/libm.so.6
Reading symbols from /lib/libgcc_s.so.1...(no debugging symbols found)...done.
Loaded symbols for /lib/libgcc_s.so.1
Reading symbols from /lib/libc.so.6...Reading symbols from /usr/lib/debug/lib/libc-2.12.1.so...done.
done.
Loaded symbols for /lib/libc.so.6
Reading symbols from /lib64/ld-linux-x86-64.so.2...Reading symbols from /usr/lib/debug/lib/ld-2.12.1.so...done.
done.
Loaded symbols for /lib64/ld-linux-x86-64.so.2
Core was generated by `./a.out'.
Program terminated with signal 11, Segmentation fault.
#0  0x00007fba1049104b in std::basic_string<char, std::char_traits<char>, std::allocator<char> >::~basic_string() () from /usr/lib/libstdc++.so.6

EDIT 2:
BTW, my hardware is not faulty as far as I know and I treat the OS quite well

EDIT 3:
Valgrind reports the following:

==3428== Conditional jump or move depends on uninitialised value(s)
==3428==    at 0x4ECB022: std::basic_string<char, std::char_traits<char>, std::allocator<char> >::~basic_string() (in /usr/lib/libstdc++.so.6.0.14)
==3428==    by 0x400D73: A::~A() (in /home/xxx/C++/Exercises/ch04/a.out)
==3428==    by 0x400D91: B::~B() (in /home/xxx/C++/Exercises/ch04/a.out)
==3428==    by 0x400CD7: main (in /home/xxx/C++/Exercises/ch04/a.out)
==3428== 
==3428== Use of uninitialised value of size 8
==3428==    at 0x4ECB04B: std::basic_string<char, std::char_traits<char>, std::allocator<char> >::~basic_string() (in /usr/lib/libstdc++.so.6.0.14)
==3428==    by 0x400D73: A::~A() (in /home/xxx/C++/Exercises/ch04/a.out)
==3428==    by 0x400D91: B::~B() (in /home/xxx/C++/Exercises/ch04/a.out)
==3428==    by 0x400CD7: main (in /home/xxx/C++/Exercises/ch04/a.out)
==3428== 
==3428== Invalid read of size 4
==3428==    at 0x4ECB04B: std::basic_string<char, std::char_traits<char>, std::allocator<char> >::~basic_string() (in /usr/lib/libstdc++.so.6.0.14)
==3428==    by 0x400D73: A::~A() (in /home/xxx/C++/Exercises/ch04/a.out)
==3428==    by 0x400D91: B::~B() (in /home/xxx/C++/Exercises/ch04/a.out)
==3428==    by 0x400CD7: main (in /home/xxx/C++/Exercises/ch04/a.out)
==3428==  Address 0xfffffffffffffff8 is not stack'd, malloc'd or (recently) free'd
==3428== 
==3428== 
==3428== Process terminating with default action of signal 11 (SIGSEGV): dumping core
==3428==  Access not within mapped region at address 0xFFFFFFFFFFFFFFF8
==3428==    at 0x4ECB04B: std::basic_string<char, std::char_traits<char>, std::allocator<char> >::~basic_string() (in /usr/lib/libstdc++.so.6.0.14)
==3428==    by 0x400D73: A::~A() (in /home/xxx/C++/Exercises/ch04/a.out)
==3428==    by 0x400D91: B::~B() (in /home/xxx/C++/Exercises/ch04/a.out)
==3428==    by 0x400CD7: main (in /home/xxx/C++/Exercises/ch04/a.out)
==3428==  If you believe this happened as a result of a stack
==3428==  overflow in your program's main thread (unlikely but
==3428==  possible), you can try to increase the size of the
==3428==  main thread stack using the --main-stacksize= flag.
==3428==  The main thread stack size used in this run was 8388608.
==3428== 
==3428== HEAP SUMMARY:
==3428==     in use at exit: 0 bytes in 0 blocks
==3428==   total heap usage: 0 allocs, 0 frees, 0 bytes allocated
==3428== 
==3428== All heap blocks were freed -- no leaks are possible    

Answer 1

The way this is going, it seems like a bug in either the GCC/libstdc++ packaging/building, or in the version used. Try GCC 4.5 or 4.6 and if it doesn’t happen there, tell yourself to always use the latest and greatest (until that breaks something of course) and never look back.

It seems the compiler is not initializing the A member in B, which would result in std::string‘s destructor failing to read the necessary info to properly destruct itself. But this is just conjecture and guesses.