I have the following problem: recently I was trying to improve the performance of my programs using this option:
std::ios_base::sync_with_stdio( false );
which I read from here that it is useful to increase the output stream speed for std::cout.
The problem is that, if I try to compile my program prove.cpp with g and -std=c 17 flag:
#include <ios>
class foo
{
public:
void test() { std::ios_base::sync_with_stdio( false );}
};
int main
{
foo object;
object.test();
}
and run Valgrind memcheck tool on the executable, using:
valgrind --leak-check=full --show-leak-kinds=all ./a.out
I got a sort of error from Valgrind output:
==353686== Memcheck, a memory error detector
==353686== Copyright (C) 2002-2017, and GNU GPL'd, by Julian Seward et al.
==353686== Using Valgrind-3.15.0 and LibVEX; rerun with -h for copyright info
==353686== Command: ./a.out
==353686==
==353686==
==353686== HEAP SUMMARY:
==353686== in use at exit: 122,880 bytes in 6 blocks
==353686== total heap usage: 7 allocs, 1 frees, 195,584 bytes allocated
==353686==
==353686== 8,192 bytes in 1 blocks are still reachable in loss record 1 of 6
==353686== at 0x483C583: operator new[](unsigned long) (in /usr/lib/x86_64-linux-gnu/valgrind/vgpreload_memcheck-amd64-linux.so)
==353686== by 0x4977D03: std::basic_filebuf<char, std::char_traits<char> >::_M_allocate_internal_buffer() (in /usr/lib/x86_64-linux-gnu/libstdc .so.6.0.28)
==353686== by 0x4975AD9: ??? (in /usr/lib/x86_64-linux-gnu/libstdc .so.6.0.28)
==353686== by 0x4927AA7: std::ios_base::sync_with_stdio(bool) (in /usr/lib/x86_64-linux-gnu/libstdc .so.6.0.28)
==353686== by 0x10926B: foo::test() (in /home/gianluca/a.out)
==353686== by 0x1091CF: main (in /home/gianluca/a.out)
==353686==
==353686== 8,192 bytes in 1 blocks are still reachable in loss record 2 of 6
==353686== at 0x483C583: operator new[](unsigned long) (in /usr/lib/x86_64-linux-gnu/valgrind/vgpreload_memcheck-amd64-linux.so)
==353686== by 0x4977D03: std::basic_filebuf<char, std::char_traits<char> >::_M_allocate_internal_buffer() (in /usr/lib/x86_64-linux-gnu/libstdc .so.6.0.28)
==353686== by 0x4975AD9: ??? (in /usr/lib/x86_64-linux-gnu/libstdc .so.6.0.28)
==353686== by 0x4927AC8: std::ios_base::sync_with_stdio(bool) (in /usr/lib/x86_64-linux-gnu/libstdc .so.6.0.28)
==353686== by 0x10926B: foo::test() (in /home/gianluca/a.out)
==353686== by 0x1091CF: main (in /home/gianluca/a.out)
==353686==
==353686== 8,192 bytes in 1 blocks are still reachable in loss record 3 of 6
==353686== at 0x483C583: operator new[](unsigned long) (in /usr/lib/x86_64-linux-gnu/valgrind/vgpreload_memcheck-amd64-linux.so)
==353686== by 0x4977D03: std::basic_filebuf<char, std::char_traits<char> >::_M_allocate_internal_buffer() (in /usr/lib/x86_64-linux-gnu/libstdc .so.6.0.28)
==353686== by 0x4975AD9: ??? (in /usr/lib/x86_64-linux-gnu/libstdc .so.6.0.28)
==353686== by 0x4927AE8: std::ios_base::sync_with_stdio(bool) (in /usr/lib/x86_64-linux-gnu/libstdc .so.6.0.28)
==353686== by 0x10926B: foo::test() (in /home/gianluca/a.out)
==353686== by 0x1091CF: main (in /home/gianluca/a.out)
==353686==
==353686== 32,768 bytes in 1 blocks are still reachable in loss record 4 of 6
==353686== at 0x483C583: operator new[](unsigned long) (in /usr/lib/x86_64-linux-gnu/valgrind/vgpreload_memcheck-amd64-linux.so)
==353686== by 0x4979B16: std::basic_filebuf<wchar_t, std::char_traits<wchar_t> >::_M_allocate_internal_buffer() (in /usr/lib/x86_64-linux-gnu/libstdc .so.6.0.28)
==353686== by 0x4975CC9: ??? (in /usr/lib/x86_64-linux-gnu/libstdc .so.6.0.28)
==353686== by 0x4927B5D: std::ios_base::sync_with_stdio(bool) (in /usr/lib/x86_64-linux-gnu/libstdc .so.6.0.28)
==353686== by 0x10926B: foo::test() (in /home/gianluca/a.out)
==353686== by 0x1091CF: main (in /home/gianluca/a.out)
==353686==
==353686== 32,768 bytes in 1 blocks are still reachable in loss record 5 of 6
==353686== at 0x483C583: operator new[](unsigned long) (in /usr/lib/x86_64-linux-gnu/valgrind/vgpreload_memcheck-amd64-linux.so)
==353686== by 0x4979B16: std::basic_filebuf<wchar_t, std::char_traits<wchar_t> >::_M_allocate_internal_buffer() (in /usr/lib/x86_64-linux-gnu/libstdc .so.6.0.28)
==353686== by 0x4975CC9: ??? (in /usr/lib/x86_64-linux-gnu/libstdc .so.6.0.28)
==353686== by 0x4927B77: std::ios_base::sync_with_stdio(bool) (in /usr/lib/x86_64-linux-gnu/libstdc .so.6.0.28)
==353686== by 0x10926B: foo::test() (in /home/gianluca/a.out)
==353686== by 0x1091CF: main (in /home/gianluca/a.out)
==353686==
==353686== 32,768 bytes in 1 blocks are still reachable in loss record 6 of 6
==353686== at 0x483C583: operator new[](unsigned long) (in /usr/lib/x86_64-linux-gnu/valgrind/vgpreload_memcheck-amd64-linux.so)
==353686== by 0x4979B16: std::basic_filebuf<wchar_t, std::char_traits<wchar_t> >::_M_allocate_internal_buffer() (in /usr/lib/x86_64-linux-gnu/libstdc .so.6.0.28)
==353686== by 0x4975CC9: ??? (in /usr/lib/x86_64-linux-gnu/libstdc .so.6.0.28)
==353686== by 0x4927B90: std::ios_base::sync_with_stdio(bool) (in /usr/lib/x86_64-linux-gnu/libstdc .so.6.0.28)
==353686== by 0x10926B: foo::test() (in /home/gianluca/a.out)
==353686== by 0x1091CF: main (in /home/gianluca/a.out)
==353686==
==353686== LEAK SUMMARY:
==353686== definitely lost: 0 bytes in 0 blocks
==353686== indirectly lost: 0 bytes in 0 blocks
==353686== possibly lost: 0 bytes in 0 blocks
==353686== still reachable: 122,880 bytes in 6 blocks
==353686== suppressed: 0 bytes in 0 blocks
==353686==
==353686== For lists of detected and suppressed errors, rerun with: -s
==353686== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)
Do you know how to solve it? Should I suppress it? Thanks.
CodePudding user response：
Based on other's answers, it seems that there is no easy solution to the problem. However, since this is a not so relevant issue and memory is reclaimed when my program exits, I concluded that the most suitable "solution" is to add these specific errors to a Valgrind suppression file.