void str_vec::reallocate()
{
auto new_capacity = size()>1?size()*2:1;
auto new_data = alloc.allocate(new_capacity);
auto dest = new_data;
auto elem = elements;
for(std::size_t i = 0;i<size();++i)
alloc.construct(dest++,std::move(*elem++));
free();
elements = new_data;
first_free = dest;
std::cout << cap - elements << std::endl;
cap = new_data+new_capacity;
}
/**
* @brief allocate memory for spicified number of elements
* @param n
* @note it's user's responsibility to ensure that @param n is greater than
* the current capacity.
*/
void StrVec::wy_alloc_n_move(std::size_t n)
{
std::size_t newCapacity = n;
std::string*
newData = alloc.allocate(newCapacity);
std::string*
dest = newData;
std::string*
elem = element;
//! move the old to newly allocated space.
for (std::size_t i = 0; i != size(); ++i)
alloc.construct(dest++, std::move(*elem++));
free();
//! update data structure
element = newData;
first_free = dest;
cap = element + newCapacity;
}
/**
* @brief allocate new room if nessary and push back the new string
* @param s new string
*/
void StrVec::push_back(const std::string& s)
{
chk_n_alloc();
alloc.construct(first_free++, s);
}
void reallocate()
{
auto newcap = size() ? size()*2 : 1;
auto newspace = alloc.allocate(newcap);
std::cout << "reallocate: size() " << size() << std::endl;
auto dest = newspace;
auto source = element_;
// move the data from the old memory to the new
// std::move() returns rvalue, which cause construct() to use string
// move ctor.
//
// seg-fault when have a typo and use element in the loop:
//
// for (size_t i = 0; i != size(); ++i)
// alloc.construct(dest++, std::move(*element_++));
//
// *gdb-debug* bt when use -g
// Program terminated with signal SIGSEGV, Segmentation fault.
// #0 0x00007f94aa120113 in std::basic_string<char, std::char_traits<char>, std::allocator<char> >::basic_string(std::string&&) () from /usr/lib/x86_64-linux-gnu/libstdc++.so.6
// (gdb) bt
// #0 0x00007f94aa120113 in std::basic_string<char, std::char_traits<char>, std::allocator<char> >::basic_string(std::string&&) () from /usr/lib/x86_64-linux-gnu/libstdc++.so.6
// #1 0x0000000000401bf7 in __gnu_cxx::new_allocator<std::string>::construct<std::string<std::string> > (this=0x602cd1 <StrVec::alloc>, __p=0xa53000) at /usr/include/c++/4.9/ext/new_allocator.h:120
// #2 0x0000000000401932 in StrVec::reallocate (this=0x7ffdc9026bc0) at t_ex_strvec.cpp:117
// #3 0x0000000000401aa5 in StrVec::check_and_alloc (this=0x7ffdc9026bc0) at t_ex_strvec.cpp:147
// #4 0x000000000040165e in StrVec::push_back (this=0x7ffdc9026bc0, s="two") at t_ex_strvec.cpp:44
// #5 0x000000000040133e in main () at t_ex_strvec.cpp:198
//
// when not use -g
// (gdb) bt
// #0 0x00007f3348f5c113 in std::basic_string<char, std::char_traits<char>, std::allocator<char> >::basic_string(std::string&&) () from /usr/lib/x86_64-linux-gnu/libstdc++.so.6
// #1 0x0000000000401bf7 in void __gnu_cxx::new_allocator<std::string>::construct<std::string, std::string>(std::string*, std::string&&) ()
// #2 0x0000000000401932 in StrVec::reallocate() ()
// #3 0x0000000000401aa5 in StrVec::check_and_alloc() ()
// #4 0x000000000040165e in StrVec::push_back(std::string const&) ()
// #5 0x000000000040133e in main ()
//
// How to debug? See that uses 'construct' and gdb is useful to see
// what's going on when stepping through. Found out that the loop
// continues and saw that when add to print i and size().
//
// ...
// i: 16856, size: 18446744073709534761
// Segmentation fault (core dumped)
//
// (gdb) f 2
// #2 0x0000000000401932 in StrVec::reallocate (this=0x7ffdc9026bc0) at t_ex_strvec.cpp:117
// 117 alloc.construct(dest++, std::move(*element_++));
// (gdb) p i
// $1 = 16856
// (gdb) p/u free_-element_
// $6 = 18446744073709534760
//
// Why? Since element_ is member data and keep increasing it, then
// size() member function would produce negative which turns into
// big number sicne size() returns size_t, unsigned int.
for (size_t i = 0; i != size(); ++i)
{
// std::cout << "i: " << i << ", size: " << size() << std::endl;
alloc.construct(dest++, std::move(*source++));
}
// std::cout.flush();
// std::this_thread::sleep_for(std::chrono::seconds{5});
// to point the new space
element_ = newspace;
free_ = dest;
cap_ = element_ + newcap;
}