Please consider the program below (backtrace included (gcc 4.0.2
(Ubuntu))). The program crashes when doing a std::slice on a valarray
containing a structure with a string element in it.
Is what I am doing there undefined behaviour? I've read 26.3.4 from
the standard but got no clues.
As you can see in the backtrace the segfault happens when trying to
assign this string:
(gdb) print *__a
...
y = {
static npos = 18446744073709551615,
_M_dataplus = {
<std::allocator<char>> = {
<__gnu_cxx::__mt_alloc<char,__gnu_cxx::__common_pool_policy<__gnu_cxx::__pool,
true> >> = {
<__gnu_cxx::__mt_alloc_base<char>> = {<No data fields>}, <No data
fields>}, <No data fields>},
members of
std::basic_string<char,std::char_traits<char>,std::allocator<char>
>::_Alloc_hider:
_M_p = 0x2aaaaadb9958 ""
}
to this string:
(gdb) print *__b
...
y = {
static npos = 18446744073709551615,
_M_dataplus = {
<std::allocator<char>> = {
<__gnu_cxx::__mt_alloc<char,__gnu_cxx::__common_pool_policy<__gnu_cxx::__pool,
true> >> = {
<__gnu_cxx::__mt_alloc_base<char>> = {<No data fields>}, <No data
fields>}, <No data fields>},
members of
std::basic_string<char,std::char_traits<char>,std::allocator<char>
>::_Alloc_hider:
_M_p = 0x0
}
I am not sure why *__b is a 0x0-string, and who should be responsible
to initialize it correctly (__b is initialized in the C++ library). It
is mandated by the standard that only POD types are allowed in a
valarray?
Thanks,
(The program crashes with gcc 3.x und gcc 4.x, it works with Visual
Studio though :-().
--8<---------------cut here---------------start------------->8---
#include <valarray>
struct element
{
int x;
std::string y;
element ()
{
x = 0;
y = "";
}
element const & operator = (element const & e)
{
if (this != &e)
{
x = e.x;
y = e.y; // Why is this.y = 0x0 ?
}
return *this;
}
};
int main (int argc, char **argv)
{
std::valarray <element> y (element (), 1);
std::valarray <element> z =
std::valarray <element> (y [std::slice (0, 1, 1)]);
return 0;
}
Core was generated by `./a.out'.
Program terminated with signal 11, Segmentation fault.
(gdb) bt
#0 0x00002aaaaac80d52 in __gnu_cxx::__exchange_and_add () from
/usr/lib/libstdc++.so.6
(gdb) bt
#0 0x00002aaaaac80d52 in __gnu_cxx::__exchange_and_add () from
/usr/lib/libstdc++.so.6
#1 0x00002aaaaac61edc in std::string::assign () from /usr/lib/libstdc++.so.6
#2 0x0000000000400c33 in element::operator= (this=0x502030, [EMAIL PROTECTED])
at valarray_segfault.cpp:19
#3 0x0000000000400f9f in std::__valarray_copy<element> (__a=0x502010, __n=1,
__s=1, __b=0x502030) at valarray_array.h:293
#4 0x0000000000400ff9 in std::__valarray_copy<element> (__a={_M_data =
0x502010}, __n=1, __s=1, __b={_M_data = 0x502030}) at valarray_array.h:457
#5 0x0000000000401065 in valarray (this=0x7ffffffb1980, [EMAIL PROTECTED]) at
valarray:587
#6 0x0000000000400961 in main (argc=1, argv=0x7ffffffb1ad8) at
valarray_segfault.cpp:30
(gdb) frame 3
#3 0x0000000000400f9f in std::__valarray_copy<element> (__a=0x502010, __n=1,
__s=1, __b=0x502030) at valarray_array.h:293
293 *__b = *__a;
(gdb) print *__b
$1 = {
x = 0,
y = {
static npos = 18446744073709551615,
_M_dataplus = {
<std::allocator<char>> = {
<__gnu_cxx::__mt_alloc<char,__gnu_cxx::__common_pool_policy<__gnu_cxx::__pool,
true> >> = {
<__gnu_cxx::__mt_alloc_base<char>> = {<No data fields>}, <No data
fields>}, <No data fields>},
members of
std::basic_string<char,std::char_traits<char>,std::allocator<char>
>::_Alloc_hider:
_M_p = 0x0
}
}
}
(gdb) print *__a
$2 = {
x = 0,
y = {
static npos = 18446744073709551615,
_M_dataplus = {
<std::allocator<char>> = {
<__gnu_cxx::__mt_alloc<char,__gnu_cxx::__common_pool_policy<__gnu_cxx::__pool,
true> >> = {
<__gnu_cxx::__mt_alloc_base<char>> = {<No data fields>}, <No data
fields>}, <No data fields>},
members of
std::basic_string<char,std::char_traits<char>,std::allocator<char>
>::_Alloc_hider:
_M_p = 0x2aaaaadb9958 ""
}
}
}
(gdb)
--8<---------------cut here---------------end--------------->8---
--
--Jhair
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