segfault "caused" by unused variable in different class

micha_eleric

i dont get why or how changing a variable in a different class "causes" a segfault, when the variable is not called. makes me wander if it is a symptom of a unrelated issue.

using linux, Qt Creator, c++,

void Class2::Print(std::string s)
    {
        m_file << s << '\n' << std::flush;
        std::cout << s << '\n' << std::flush;
    }

std::ofstream m_file;
m_file.open("Class2OutputFile.txt");

Print() is called 22 times no issue.

connect(m_ui->pushButton_35, &QPushButton::clicked,this, &Class1::Btn_ABCParam);
connect(m_ui->pushButton_32, &QPushButton::clicked,this, &Class1::Btn_XYZParam);

"causes" sigfault, but never does anything with

while(i < m_vPointA.size())
or 
while(i < (m_iNewPoint + 1))

debug showed what was crashing program.
if i push a button that DOES call a function that DOES deal with m_iNewPoint or m_vPointA, then no crash, all works as should.

Btn_ABCParam and Btn_XYZParam, sends values to Class2, which does nothing with m_iNewPoint nor m_vPointA.

as long as

Class1::DisPlayView()
Class1::PrintLocation()
Class1::PrintLocationStepMtrPst()

dont get to last element of m_vPointA, then Class2::Print() has no issue with (std::string s)

i am wandering if the real issue is also causing : https://forum.qt.io/topic/142392/dont-know-what-to-call-error-bug-part-of-string-printed-to-file-and-konsole-without-calling-cout-or-std-ofstream-m_file/4

i have made a new project, and added my code to new project. same error

Christian Ehrlicher

Please provide a minimal, compilable example to reproduce your issue - it's impossible to see something from your code fragments...
Apart from this - unitinitalized variables may contain anything so everything can happen when they are accessed.

micha_eleric

@Christian-Ehrlicher said in segfault "caused" by unused variable in different class:

Please provide a minimal, compilable example to reproduce your issue - it's impossible to see something from your code fragments...
Apart from this - unitinitalized variables may contain anything so everything can happen when they are accessed.

the variable ARE NOT accessed, uninitialized or initialized
to repeat what i already said, variable that is "causing" sigfault, has absolutely nothing to do with the function that sigfault occurs in.

at first i thought m_iNewPoint was causing the crash, because if i changed m_iNewPoint [which is at minimum initializing] to one less than size of m_vPointA, then there was no crash.

Class2 has only one function, that tells Class1 to do anything with m_vPointA nor m_iNewPoint. Class2 does not have any functions that call m_vPointA nor m_iNewPoint. Only Class1 can touch m_vPointA or m_iNewPoint.

The minimum code, would be the whole project.

anything done in Class1 that uses m_vPointA or m_iNewPoint, doe not "cause" a sigfault.

It is like putting fuel in a car in mexico, and a house in canada explodes.

ChrisW67

The moral of the story... don't refuel in Mexico!

All we can say is that:

if executing the two connect() calls causes a segfault then m_ui, m_ui->pushButton_35, and m_ui->pushButton_32 are all candidates for being uninitialised or undefined.
if executing whatever is in Class1::Btn_ABCParam() or Class1::Btn_XYZParam() causes the segfault then the problem is there.

Any other relationship between these two connect() statements and anything else in your post is unclear.

as long as

Class1::DisPlayView()
Class1::PrintLocation()
Class1::PrintLocationStepMtrPst()

dont get to last element of m_vPointA, then Class2::Print() has no issue with (std::string s)

This strongly suggests one, some, or all, of these methods runs off the end of a list, attempt out of bounds access of m_vPointA (whatever that object is), or that last element in m_vPointA is invalid or undefined.

Run your program in the debugger and, when it crashes, copy and paste:

the ASSERT or other output from the console
the entire stack back trace
the lines of code around the first line or your code mentioned in the back trace

micha_eleric

@ChrisW67 said in segfault "caused" by unused variable in different class:

The moral of the story... don't refuel in Mexico!

All we can say is that:

if executing the two connect() calls causes a segfault then m_ui, m_ui->pushButton_35, and m_ui->pushButton_32 are all candidates for being uninitialised or undefined.

if executing whatever is in Class1::Btn_ABCParam() or Class1::Btn_XYZParam() causes the segfault then the problem is there.

this makes sense, but does not explain allowing unrelated code being able to see last element of m_vPointA, that is not called.

Any other relationship between these two connect() statements and anything else in your post is unclear.

as long as

Class1::DisPlayView()
Class1::PrintLocation()
Class1::PrintLocationStepMtrPst()

dont get to last element of m_vPointA, then Class2::Print() has no issue with (std::string s)

there is not relations, other then being in Class1 with the two buttons connects. that is why i did not look at those the two functions that are connected to the two buttons

This strongly suggests one, some, or all, of these methods runs off the end of a list, attempt out of bounds access of m_vPointA (whatever that object is), or that last element in m_vPointA is invalid or undefined.

"strongly suggests" but as i said several times, m_iNewPoint is initialized, and m_vPointA is accessed one less than m_vPointA.size(), by different methods, does not "cause" sigfault, but m_iNewPoint == m_vPointA.size() does "cause" sigfault.

Run your program in the debugger and, when it crashes, copy and paste:

the ASSERT or other output from the console

the entire stack back trace

the lines of code around the first line or your code mentioned in the back trace

ok

micha_eleric

@ChrisW67 said in segfault "caused" by unused variable in different class:

Run your program in the debugger and, when it crashes, copy and paste:

the ASSERT or other output from the console

nothing

the entire stack back trace

i would like to know where to find stack. dont see a button/tab for stack

the lines of code around the first line or your code mentioned in the back trace

micha_eleric

@ChrisW67 said in segfault "caused" by unused variable in different class:

i found this. no clue what it is

        5022 [1]	    {
0x55842709e972                  f3 0f 1e fa           endbr64
0x55842709e976  <+    4>        55                    push   %rbp
0x55842709e977  <+    5>        48 89 e5              mov    %rsp,%rbp
0x55842709e97a  <+    8>        48 83 ec 10           sub    $0x10,%rsp
0x55842709e97e  <+   12>        48 89 7d f8           mov    %rdi,-0x8(%rbp)
0x55842709e982  <+   16>        48 89 75 f0           mov    %rsi,-0x10(%rbp)
        5023 [1]	        m_file << s << '\n' << std::flush;
0x55842709e986  <+   20>        48 8b 45 f8           mov    -0x8(%rbp),%rax
0x55842709e98a  <+   24>        48 8d 50 18           lea    0x18(%rax),%rdx
0x55842709e98e  <+   28>        48 8b 45 f0           mov    -0x10(%rbp),%rax
0x55842709e992  <+   32>        48 89 c6              mov    %rax,%rsi
0x55842709e995  <+   35>        48 89 d7              mov    %rdx,%rdi
0x55842709e998  <+   38>        e8 f3 3b fd ff        callq  0x558427072590 <_ZStlsIcSt11char_traitsIcESaIcEERSt13basic_ostreamIT_T0_ES7_RKNSt7__cxx1112basic_stringIS4_S5_T1_EE@plt>
0x55842709e99d  <+   43>        be 0a 00 00 00        mov    $0xa,%esi
0x55842709e9a2  <+   48>        48 89 c7              mov    %rax,%rdi
0x55842709e9a5  <+   51>        e8 96 36 fd ff        callq  0x558427072040 <_ZStlsISt11char_traitsIcEERSt13basic_ostreamIcT_ES5_c@plt>
0x55842709e9aa  <+   56>        48 89 c2              mov    %rax,%rdx
0x55842709e9ad  <+   59>        48 8b 05 0c 46 07 00  mov    0x7460c(%rip),%rax        # 0x558427112fc0
0x55842709e9b4  <+   66>        48 89 c6              mov    %rax,%rsi
0x55842709e9b7  <+   69>        48 89 d7              mov    %rdx,%rdi
0x55842709e9ba  <+   72>        e8 e1 3e fd ff        callq  0x5584270728a0 <_ZNSolsEPFRSoS_E@plt>
        5024 [1]	        std::cout << s << '\n' << std::flush;
0x55842709e9bf  <+   77>        48 8b 45 f0           mov    -0x10(%rbp),%rax
0x55842709e9c3  <+   81>        48 89 c6              mov    %rax,%rsi
0x55842709e9c6  <+   84>        48 8b 05 9b 45 07 00  mov    0x7459b(%rip),%rax        # 0x558427112f68
0x55842709e9cd  <+   91>        48 89 c7              mov    %rax,%rdi
0x55842709e9d0  <+   94>        e8 bb 3b fd ff        callq  0x558427072590 <_ZStlsIcSt11char_traitsIcESaIcEERSt13basic_ostreamIT_T0_ES7_RKNSt7__cxx1112basic_stringIS4_S5_T1_EE@plt>
0x55842709e9d5  <+   99>        be 0a 00 00 00        mov    $0xa,%esi
0x55842709e9da  <+  104>        48 89 c7              mov    %rax,%rdi
0x55842709e9dd  <+  107>        e8 5e 36 fd ff        callq  0x558427072040 <_ZStlsISt11char_traitsIcEERSt13basic_ostreamIcT_ES5_c@plt>
0x55842709e9e2  <+  112>        48 89 c2              mov    %rax,%rdx
0x55842709e9e5  <+  115>        48 8b 05 d4 45 07 00  mov    0x745d4(%rip),%rax        # 0x558427112fc0
0x55842709e9ec  <+  122>        48 89 c6              mov    %rax,%rsi
0x55842709e9ef  <+  125>        48 89 d7              mov    %rdx,%rdi
0x55842709e9f2  <+  128>        e8 a9 3e fd ff        callq  0x5584270728a0 <_ZNSolsEPFRSoS_E@plt>
        5025 [1]	    }
0x55842709e9f7  <+  133>        90                    nop
0x55842709e9f8  <+  134>        c9                    leaveq
0x55842709e9f9  <+  135>        c3                    retq

ChrisW67

Ensure you build a debug version of your project:

then run the program in the debugger:

generate the crash:

then look at the debugger panes at the bottom of your screen. The left panel is the back trace (yours will be longer). Right-click to copy the text:

Select the top-most line in the back trace that is in your code. There is a panel that shows the variables in scope at the time of the call selected.

micha_eleric

@ChrisW67 the panel that shows variables, is open by default, and has no title. it says
s <not accessible> std::string
which is weird, every call to Print(), has a string

what was copied to clip board:
1 std::ostream::sentry::sentry(std::ostream&) 0x7f5783825f27
2 std::basic_ostream<char, std::char_traits<char>>& std::__ostream_insert<char, std::char_traits<char>>(std::basic_ostream<char, std::char_traits<char>>&, const char *, long) 0x7f57838266cc
3 Class2::Print CControls.cpp 5023 0x55db831e499d
4 Class2::CheckABCParam CControls.cpp 39 0x55db831b9036
5 Class3::CheckABCParam Class3.cpp 90 0x55db8322a1ce
6 Class1::Btn_ABCParam CGUI.cpp 856 0x55db831f9599
7 QtPrivate::FunctorCall<QtPrivate::IndexesList<>, QtPrivate::List<>, void, void (Class1:: *)()>::call(void (Class1:: *)(), Class1 *, void * *) qobjectdefs_impl.h 152 0x55db83228a69
8 QtPrivate::FunctionPointer<void (Class1:: *)()>::call<QtPrivate::List<>, void>(void (Class1:: *)(), Class1 *, void * *) qobjectdefs_impl.h 185 0x55db8322879a
9 QtPrivate::QSlotObject<void (Class1:: *)(), QtPrivate::List<>, void>::impl(int, QtPrivate::QSlotObjectBase *, QObject *, void * *, bool *) qobjectdefs_impl.h 414 0x55db832281c8
10 QMetaObject::activate(QObject *, int, int, void * *) 0x7f5783b87328
11 QAbstractButton::clicked(bool) 0x7f5784683806
12 ?? 0x7f5784683a2e
13 ?? 0x7f5784684e73
14 QAbstractButton::mouseReleaseEvent(QMouseEvent *) 0x7f5784685035
15 QWidget::event(QEvent *) 0x7f57845d12b6
16 QApplicationPrivate::notify_helper(QObject *, QEvent *) 0x7f578458ea66
17 QApplication::notify(QObject *, QEvent *) 0x7f5784598343
18 QCoreApplication::notifyInternal2(QObject *, QEvent *) 0x7f5783b5b80a
19 QApplicationPrivate::sendMouseEvent(QWidget *, QMouseEvent *, QWidget *, QWidget *, QWidget * *, QPointer<QWidget>&, bool, bool) 0x7f5784597457
20 ?? 0x7f57845ed35d
... <More>

it does not explain how changing a variable for a vector, that is not used, is causing a string to be empty, that has nothing to do with the changed variable, nor a vector

micha_eleric

????????
i replace

while(i < (m_vPointA.size() - 0))

with

while(i < (m_vPointA.size() - 1))

so i can move on. getting the last value in vectors are not a big deal, what is causing the unrelated segfault, is.

got another unrelated segfault at same point by removing

m_sState = "stop"

, but this time in Class2, which also has absolutely nothing to do with

Class2::CheckABCParam()

, sending a string to

Class2::Print()

???????????????????????????????????????????????????????????
remove all 6

m_sState = "stop"

at same time, it segfaults in unrelated code
remove one at a time, run debug, repeat untill all 6 are removed, and it does not????????

Kent-Dorfman

I detect a strong odor of pointer problems.

micha_eleric

@Kent-Dorfman said in segfault "caused" by unused variable in different class:

I detect a strong odor of pointer problems.

i am getting random segfault at

Class2::Print()

, but most dont occur everytime. the one involving

(m_vPointA.size()

is the only one that occurred every time for two days

lets go with pointer error. how to track it down?