Valgrind Error: in use at exit: 72,704 bytes C++ Initialization List weirdness with char*

Question

Issue:

I have a weird issue that I wasn't expecting. I have a class called Answers and within the header is this:

class Answer
{
    char* aText;
    bool b_correct;
public:
    Answer():aText(0){;}  //default constructor
}

The main (testing) driver code is this:

int main(void) 
{

    static const unsigned int MAX_ANSWERS = 5;
    Answer answers[MAX_ANSWERS];
}

The (unexpected) weirdness I am getting is that there is an alloc happening, and I haven't used a new anywhere in my code yet. I'm guessing that the char* is calling this in the initialization list.

I am using valgrind to test my code, and I'm getting 11 allocs and 10 frees. When I remove the initializer of :aText(0), the extra alloc goes away.

I get that this is badly constructed code. I am following a course outline to learn how to write in C++. Can someone please help me understand how the memory is allocated or what's happening during the initialization list to cause a call to new?

I know the error is coming from the code shown. I know the extra alloc is happening When I compile and run just this code.

Valgrind Output:

==12598== Memcheck, a memory error detector
==12598== Copyright (C) 2002-2013, and GNU GPL'd, by Julian Seward et al.
==12598== Using Valgrind-3.10.1 and LibVEX; rerun with -h for copyright info
==12598== Command: ./Answers
==12598== 
==12598== 
==12598== HEAP SUMMARY:
==12598==     in use at exit: 72,704 bytes in 1 blocks
==12598==   total heap usage: 1 allocs, 0 frees, 72,704 bytes allocated
==12598== 
==12598== LEAK SUMMARY:
==12598==    definitely lost: 0 bytes in 0 blocks
==12598==    indirectly lost: 0 bytes in 0 blocks
==12598==      possibly lost: 0 bytes in 0 blocks
==12598==    still reachable: 72,704 bytes in 1 blocks
==12598==         suppressed: 0 bytes in 0 blocks
==12598== Rerun with --leak-check=full to see details of leaked memory
==12598== 
==12598== For counts of detected and suppressed errors, rerun with: -v
==12598== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)

Platform Information:

Fedora 22

gcc.x86_64 5.1.1-4.fc22

valgrind.x86_64 1:3.10.1-13.fc22

codeblocks.x86_64 13.12-14.fc22

Get rid of the ... and post a full class that shows what you're observing. You're potentially hiding code behind those ... that causes the allocation to occur. — PaulMcKenzie
– PaulMcKenzie, Commented Aug 2, 2015 at 18:22
Why do you say there are allocations happening? Because of valgrind? Also, well-written C++ code will not any any explicit calls to new, but will have lots of automatic allocations behind the scenes. Do not make the mistake of thinking that writing C++ is about calling new and delete. — Aaron McDaid
– Aaron McDaid, Commented Aug 2, 2015 at 18:25
I didn't want to post code that wasn't important to the problem. I set up breaks in my code, and this is all that is running for me to get an alloc... and yes, valgrind said that it has happened. Is it a problem with valgrind? — user2470057
– user2470057, Commented Aug 2, 2015 at 18:27
@user2470057 I didn't want to post code that wasn't important to the problem Then post a complete example that shows the issue. Code that you may believe is not important may well be important. Or remove those ellipses, complete the class by giving it a trailing semicolon, stick it above main(), and remove the ellipses from main. — PaulMcKenzie
– PaulMcKenzie, Commented Aug 2, 2015 at 18:28
OK seriously, the rest of the code is unimportant. I just ran valgrind with this current code (... removed)... and I got this: ==11857== HEAP SUMMARY: ==11857== in use at exit: 72,704 bytes in 1 blocks ==11857== total heap usage: 1 allocs, 0 frees, 72,704 bytes allocated ==11857== still reachable: 72,704 bytes in 1 blocks — user2470057
– user2470057, Commented Aug 2, 2015 at 18:42

user2470057 · Accepted Answer · 2015-08-04 18:40:30Z

15

This is a known GCC 5.1 bug, not a valgrind bug.

Details here: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64535

Possible workarounds: Downgrade GCC to an earlier version or wait for Valgrind to update a fix for this error. Both solutions are being worked on by their respective communities.

edited Aug 4, 2015 at 18:40

answered Aug 3, 2015 at 2:51

user2470057

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6 Comments

Dominic Farolino Over a year ago

Any developments?

Crouching Kitten Over a year ago

Bug is still present in 5.4

bremen_matt Over a year ago

I must be misunderstanding something because I get exactly the same Valgrind error when I compile with Clang 3.8

Arjun Menon Over a year ago

I too get the exact same error with both Clang and GCC, on Travis CI. Here is an example of the leak with GCC and the leak with Clang. (The valgrind error appears toward the very end.)

Arjun Menon Over a year ago

The right answer is likely the one in: stackoverflow.com/questions/30376601/…

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