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From: martin@v.loewis.de To: gcc-gnats@gcc.gnu.org Subject: libstdc++/4960: std::string slow to append individual characters Date: Wed, 21 Nov 2001 12:36:00 -0000 [thread overview] Message-ID: <200111272301.fARN1Kb02682@mira.informatik.hu-berlin.de> (raw) >Number: 4960 >Category: libstdc++ >Synopsis: std::string slow to append individual characters >Confidential: no >Severity: non-critical >Priority: medium >Responsible: unassigned >State: open >Class: change-request >Submitter-Id: net >Arrival-Date: Tue Nov 27 15:06:00 PST 2001 >Closed-Date: >Last-Modified: >Originator: Martin v. Loewis >Release: 3.1 20010813 (experimental) >Organization: HUB >Environment: System: Linux mira 2.4.10-4GB #1 Tue Sep 25 12:33:54 GMT 2001 i686 unknown Architecture: i686 host: i686-pc-linux-gnu build: i686-pc-linux-gnu target: i686-pc-linux-gnu configured with: /usr/src/egcs/configure --prefix=/usr/local/newabi --enable-shared --enable-threads --enable-languages=c,c++,java >Description: In gcc 2.95, adding one character after another to an std::string resulted in infrequent memory allocations, as the implementation would reserve sufficient memory. In libstdc++ v3, each append invocation will cause reallocation (and copying of the existing string) once the reserve is exhausted. >How-To-Repeat: Compile and benchmark the following program with both gcc 2.95 and gcc 3 on the same machine. On a 900MHz Pentium III, the 2.95 compilation result needs 0.01s, the gcc 3 result needs 4.0s. #include <string> #include <stdio.h> int main() { std::string s; int i; for(i=0;i<100000;i++){ //printf("%d %d\n",i,s.capacity()); s+=" "; } } >Fix: Add a reserve larger than the current size in std::string::append. The strategy of libstdc++ 2 (using the nearest power of 2) seems reasonable. >Release-Note: >Audit-Trail: >Unformatted:
next reply other threads:[~2001-11-27 23:06 UTC|newest] Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top 2001-11-21 12:36 martin [this message] 2001-11-21 13:16 pme 2001-11-21 14:36 pme 2001-12-05 0:40 paolo 2001-12-05 0:46 paolo 2001-12-08 1:52 paolo 2001-12-08 1:56 paolo
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