[Bug 1284973] [NEW] std::array does not 0-initialise its members (per standard)

[Volodya]

Public bug reported:

Compiling the following example code:

#include <iostream>
#include <array>


int main(int argc, char* argv[])
{
	char a1[10];
	std::array<char, 10> a2;
	
	for(int i=0; i<10; i++)
	{
		std::cout << "a1[" << i << "] = " << (int)a1[i] << std::endl;
	}
	for(int i=0; i<10; i++)
	{
		std::cout << "a2[" << i << "] = " << (int)a2[i] << std::endl;
	}
}


compiling with:
g++ -std=c++11 arrays.cpp


produces the following:
$ ./a.out 
a1[0] = -36
a1[1] = -101
a1[2] = -13
a1[3] = -65
a1[4] = 85
a1[5] = -118
a1[6] = 70
a1[7] = -73
a1[8] = -16
a1[9] = -43
a2[0] = 113
a2[1] = -73
a2[2] = 0
a2[3] = 0
a2[4] = 0
a2[5] = 0
a2[6] = -37
a2[7] = -119
a2[8] = 4
a2[9] = 8


Somehow at least some of the members of std::array retain their non-zero values, which goes against C++11 standard.

Interesting to note that four values do get zero-filled (regardless of
the size of the array) on a reasonably large array, but not others. It
may, of course, but just a lucky fluke.

ProblemType: Bug
DistroRelease: Ubuntu 13.10
Package: g++ 4:4.8.1-2ubuntu3
ProcVersionSignature: Ubuntu 3.11.0-17.31-generic 3.11.10.3
Uname: Linux 3.11.0-17-generic i686
ApportVersion: 2.12.5-0ubuntu2.2
Architecture: i386
Date: Wed Feb 26 08:48:34 2014
InstallationDate: Installed on 2013-12-22 (65 days ago)
InstallationMedia: Ubuntu 13.10 "Saucy Salamander" - Release i386 (20131016.1)
MarkForUpload: True
SourcePackage: gcc-defaults
UpgradeStatus: No upgrade log present (probably fresh install)

** Affects: gcc-defaults (Ubuntu)
     Importance: Undecided
         Status: New


** Tags: apport-bug i386 saucy

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https://bugs.launchpad.net/bugs/1284973

Title:
  std::array does not 0-initialise its members (per standard)

Status in “gcc-defaults” package in Ubuntu:
  New

Bug description:
  Compiling the following example code:

  #include <iostream>
  #include <array>

  
  int main(int argc, char* argv[])
  {
  	char a1[10];
  	std::array<char, 10> a2;
  	
  	for(int i=0; i<10; i++)
  	{
  		std::cout << "a1[" << i << "] = " << (int)a1[i] << std::endl;
  	}
  	for(int i=0; i<10; i++)
  	{
  		std::cout << "a2[" << i << "] = " << (int)a2[i] << std::endl;
  	}
  }

  
  compiling with:
  g++ -std=c++11 arrays.cpp

  
  produces the following:
  $ ./a.out 
  a1[0] = -36
  a1[1] = -101
  a1[2] = -13
  a1[3] = -65
  a1[4] = 85
  a1[5] = -118
  a1[6] = 70
  a1[7] = -73
  a1[8] = -16
  a1[9] = -43
  a2[0] = 113
  a2[1] = -73
  a2[2] = 0
  a2[3] = 0
  a2[4] = 0
  a2[5] = 0
  a2[6] = -37
  a2[7] = -119
  a2[8] = 4
  a2[9] = 8

  
  Somehow at least some of the members of std::array retain their non-zero values, which goes against C++11 standard.

  Interesting to note that four values do get zero-filled (regardless of
  the size of the array) on a reasonably large array, but not others. It
  may, of course, but just a lucky fluke.

  ProblemType: Bug
  DistroRelease: Ubuntu 13.10
  Package: g++ 4:4.8.1-2ubuntu3
  ProcVersionSignature: Ubuntu 3.11.0-17.31-generic 3.11.10.3
  Uname: Linux 3.11.0-17-generic i686
  ApportVersion: 2.12.5-0ubuntu2.2
  Architecture: i386
  Date: Wed Feb 26 08:48:34 2014
  InstallationDate: Installed on 2013-12-22 (65 days ago)
  InstallationMedia: Ubuntu 13.10 "Saucy Salamander" - Release i386 (20131016.1)
  MarkForUpload: True
  SourcePackage: gcc-defaults
  UpgradeStatus: No upgrade log present (probably fresh install)

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