Hi,
I tested the following behaviour with all gcc versions I had available (gcc
3.3.6 on x86 Slackware Linux, gcc 4.0.2 on x86 SUSE Linux, gcc 4.0.1 on OS X).
The following code:
std::string s1;
// in the following call memory is allocated
// and the capacity of s1 goes to 1024
s1.resize(1024);
std::string s2;
s2="abc";
// in the following call the allocated memory is freed
// so that after the assignment s1 has the same capacity as s2
s1=s2;
While this follows the standard, which says that after the assignment
s1.capacity() >= s2. capacity() must be true, it can be quite a performance hit
when doing a lot of assignments.
With gcc the following is much faster in these cases:
s1=s2.c_str();
since then the capacity stays high and the dynamic memory management is
avoided.
Alex
--
Summary: performance problem with std::string operator=(const
std::string& str);
Product: gcc
Version: 4.0.2
Status: UNCONFIRMED
Severity: enhancement
Priority: P3
Component: libstdc++
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: neundorf at kde dot org
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29037
