[Bug libstdc++/54268] New: std::string::reserve not consistent with std::vector::reserve

[Bug libstdc++/54268] New: std::string::reserve not consistent with std::vector::reserve

[vincenzo.innocente at cern dot ch]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54268

             Bug #: 54268
           Summary: std::string::reserve not consistent with
                    std::vector::reserve
    Classification: Unclassified
           Product: gcc
           Version: 4.8.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libstdc++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: vincenzo.innocente@cern.ch


as the following test shows std::string::reserve change capacity (and relocates
the underling array) even in case the argument is smaller than the current
capacity.
std::vector::reserve will instead only extend the capacity, never shirk it?
Is this intended? IN any case in pretty conducing for the naive developer…


cat stringReserve.cpp 
#include <cassert> 

#include <string>
#include <vector>
#include <iostream>
int main()
{
{
std::string foo,bar;
foo.reserve(100);
std::cout << foo.capacity() << std::endl;
std::cerr << std::hex << (size_t) foo.c_str() << std::endl;
foo.reserve(10);
std::cout << foo.capacity()<< std::endl;
std::cerr << (size_t) foo.c_str() << std::endl;
bar.reserve(100);
foo.reserve(50);
std::cout << foo.capacity() << std::endl;
std::cerr << (size_t) foo.c_str() << std::endl;
}

{
std::vector<char> foo,bar;
foo.reserve(100);
std::cout << foo.capacity() << std::endl;
std::cerr << std::hex << (size_t) (&foo.front()) << std::endl;
foo.reserve(10);
std::cout << foo.capacity() << std::endl;
std::cerr << (size_t) (&foo.front()) << std::endl;
bar.reserve(100);
foo.reserve(50);
std::cout << foo.capacity() << std::endl;
std::cerr << (size_t) (&foo.front()) << std::endl;
}

}


c++ -std=c++11 stringReserve.cpp 
./a.out
100
7fd289c03938
10
7fd289c03ae8
50
7fd289c03b18
100
7fd289c03920
100
7fd289c03920
100
7fd289c03920

[Bug libstdc++/54268] std::string::reserve not consistent with std::vector::reserve

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54268

Paolo Carlini <paolo.carlini at oracle dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|                            |DUPLICATE

--- Comment #1 from Paolo Carlini <paolo.carlini at oracle dot com> 2012-08-15 14:20:39 UTC ---
When we roll out the new implementation we can tweak it in this area. It will
be useful to know what other implementations are doing (the current, very old,
behavior is maybe perfectible but definitely intended)

*** This bug has been marked as a duplicate of bug 51359 ***

[Bug libstdc++/54268] std::string::reserve not consistent with std::vector::reserve

[vincenzo.innocente at cern dot ch]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54268

--- Comment #2 from vincenzo Innocente <vincenzo.innocente at cern dot ch> 2012-08-15 14:31:48 UTC ---
clang behaves similarly (even with -stdlib=libc++)