[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