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  • Why does std::cout convert volatile pointers to bool?

    - by Joseph Garvin
    If you try to cout a volatile pointer, even a volatile char pointer where you would normally expect cout to print the string, you will instead simply get '1' (assuming the pointer is not null I think). I assume output stream operator<< is template specialized for volatile pointers, but my question is, why? What use case motivates this behavior? Example code: #include <iostream> #include <cstring> int main() { char x[500]; std::strcpy(x, "Hello world"); int y; int *z = &y; std::cout << x << std::endl; std::cout << (char volatile*)x << std::endl; std::cout << z << std::endl; std::cout << (int volatile*)z << std::endl; return 0; } Output: Hello world 1 0x8046b6c 1

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  • Spam Assassin on windows

    - by ebeworld
    I just installed spam assassin and run for its sample ham mail as spamassassin sample-nonspam.txt, but it ended up marking it as a spam. What configuration am i missing to change? Result of the check is: From: Keith Dawson To: tbtf@world.std.com Subject: **SPAM** TBTF ping for 2001-04-20: Reviving Date: Fri, 20 Apr 2001 16:59:58 -0400 Message-Id: X-Spam-Flag: YES X-Spam-Checker-Version: SpamAssassin 3.2.3 (2007-08-08) on ebeworld-PC X-Spam-Level: **** X-Spam-Status: Yes, score=10.5 required=6.3 tests=DCC_CHECK,DIGEST_MULTIPLE, DNS_FROM_OPENWHOIS,RAZOR2_CF_RANGE_51_100,RAZOR2_CF_RANGE_E4_51_100, RAZOR2_CHECK shortcircuit=no autolearn=no version=3.2.3 MIME-Version: 1.0 Content-Type: multipart/mixed; boundary="----------=_4BF17E8E.BF8E0000" This is a multi-part message in MIME format. ------------=_4BF17E8E.BF8E0000 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit This mail is probably spam. The original message has been attached intact in RFC 822 format. Content preview: -----BEGIN PGP SIGNED MESSAGE----- TBTF ping for 2001-04-20: Reviving T a s t y B i t s f r o m t h e T e c h n o l o g y F r o n t [...] Content analysis details: (10.5 points, 6.3 required) 2.4 DNS_FROM_OPENWHOIS RBL: Envelope sender listed in bl.open-whois.org. 1.5 RAZOR2_CF_RANGE_E4_51_100 Razor2 gives engine 4 confidence level above 50% [cf: 58] 2.5 RAZOR2_CHECK Listed in Razor2 (http://razor.sf.net/) 0.5 RAZOR2_CF_RANGE_51_100 Razor2 gives confidence level above 50% [cf: 58] 3.6 DCC_CHECK Listed in DCC (http://rhyolite.com/anti-spam/dcc/) 0.0 DIGEST_MULTIPLE Message hits more than one network digest check ------------=_4BF17E8E.BF8E0000 Content-Type: message/rfc822; x-spam-type=original Content-Description: original message before SpamAssassin Content-Disposition: inline Content-Transfer-Encoding: 8bit Return-Path: Delivered-To: [email protected] Received: from europe.std.com (europe.std.com [199.172.62.20]) by mail.netnoteinc.com (Postfix) with ESMTP id 392E1114061 for ; Fri, 20 Apr 2001 21:34:46 +0000 (Eire) Received: (from daemon@localhost) by europe.std.com (8.9.3/8.9.3) id RAA09630 for tbtf-outgoing; Fri, 20 Apr 2001 17:31:18 -0400 (EDT) Received: from sgi04-e.std.com (sgi04-e.std.com [199.172.62.134]) by europe.std.com (8.9.3/8.9.3) with ESMTP id RAA08749 for ; Fri, 20 Apr 2001 17:24:31 -0400 (EDT) Received: from world.std.com (world-f.std.com [199.172.62.5]) by sgi04-e.std.com (8.9.3/8.9.3) with ESMTP id RAA8278330 for ; Fri, 20 Apr 2001 17:24:31 -0400 (EDT) Received: (from dawson@localhost) by world.std.com (8.9.3/8.9.3) id RAA26781 for tbtf@world.std.com; Fri, 20 Apr 2001 17:24:31 -0400 (EDT) Received: from sgi04-e.std.com (sgi04-e.std.com [199.172.62.134]) by europe.std.com (8.9.3/8.9.3) with ESMTP id RAA07541 for ; Fri, 20 Apr 2001 17:12:06 -0400 (EDT) Received: from world.std.com (world-f.std.com [199.172.62.5]) by sgi04-e.std.com (8.9.3/8.9.3) with ESMTP id RAA8416421 for ; Fri, 20 Apr 2001 17:12:06 -0400 (EDT) Received: from [208.192.102.193] (ppp0c199.std.com [208.192.102.199]) by world.std.com (8.9.3/8.9.3) with ESMTP id RAA14226 for ; Fri, 20 Apr 2001 17:12:04 -0400 (EDT) Mime-Version: 1.0 Message-Id: Date: Fri, 20 Apr 2001 16:59:58 -0400 To: tbtf@world.std.com From: Keith Dawson Subject: TBTF ping for 2001-04-20: Reviving Content-Type: text/plain; charset="us-ascii" Sender: tbtf-approval@world.std.com Precedence: list Reply-To: tbtf-approval@europe.std.com -----BEGIN PGP SIGNED MESSAGE----- TBTF ping for 2001-04-20: Reviving T a s t y B i t s f r o m t h e T e c h n o l o g y F r o n t Timely news of the bellwethers in computer and communications technology that will affect electronic commerce -- since 1994 Your Host: Keith Dawson ISSN: 1524-9948 This issue: < http://tbtf.com/archive/2001-04-20.html > To comment on this issue, please use this forum at Quick Topic: < http://www.quicktopic.com/tbtf/H/kQGJR2TXL6H > ________________________________________________________________________ Q u o t e O f T h e M o m e n t Even organizations that promise "privacy for their customers" rarely if ever promise "continued privacy for their former customers..." Once you cancel your account with any business, their promises of keeping the information about their customers private no longer apply... you're not a customer any longer. This is in the large category of business behaviors that individuals would consider immoral and deceptive -- and businesses know are not illegal. -- "_ankh," writing on the XNStalk mailing list ________________________________________________________________________ ..TBTF's long hiatus is drawing to a close Hail subscribers to the TBTF mailing list. Some 2,000 [1] of you have signed up since the last issue [2] was mailed on 2000-07-20. This brief note is the first of several I will send to this list to excise the dead addresses prior to resuming regular publication. While you time the contractions of the newsletter's rebirth, I in- vite you to read the TBTF Log [3] and sign up for its separate free subscription. Send "subscribe" (no quotes) with any subject to [email protected] . I mail out collected Log items on Sun- days. If you need to stay more immediately on top of breaking stories, pick up the TBTF Log's syndication file [4] or read an aggregator that does. Examples are Slashdot's Cheesy Portal [5], Userland [6], and Sitescooper [7]. If your news obsession runs even deeper and you own an SMS-capable cell phone or PDA, sign up on TBTF's WebWire- lessNow portal [8]. A free call will bring you the latest TBTF Log headline, Jargon Scout [9] find, or Siliconium [10]. Two new columnists have bloomed on TBTF since last summer: Ted By- field's roving_reporter [11] and Gary Stock's UnBlinking [12]. Late- ly Byfield has been writing in unmatched depth about ICANN, but the roving_reporter nym's roots are in commentary at the intersection of technology and culture. Stock's UnBlinking latches onto topical sub- jects and pursues them to the ends of the Net. These writers' voices are compelling and utterly distinctive. [1] http://tbtf.com/growth.html [2] http://tbtf.com/archive/2000-07-20.html [3] http://tbtf.com/blog/ [4] http://tbtf.com/tbtf.rdf [5] http://www.slashdot.org/cheesyportal.shtml [6] http://my.userland.com/ [7] http://www.sitescooper.org/ [8] http://tbtf.com/pull-wwn/ [9] http://tbtf.com/jargon-scout.html [10] http://tbtf.com/siliconia.html [11] http://tbtf.com/roving_reporter/ [12] http://tbtf.com/unblinking/ ________________________________________________________________________ S o u r c e s For a complete list of TBTF's email and Web sources, see http://tbtf.com/sources.html . ________________________________________ B e n e f a c t o r s TBTF is free. If you get value from this publication, please visit the TBTF Benefactors page < http://tbtf.com/the-benefactors.html > and consider contributing to its upkeep. ________________________________________________________________________ TBTF home and archive at http://tbtf.com/ . To unsubscribe send the message "unsubscribe" to [email protected]. TBTF is Copy- right 1994-2000 by Keith Dawson, <dawson@world.std.com>. Commercial use prohibited. For non-commercial purposes please forward, post, and link as you see fit. _______________________________________________ Keith Dawson dawson@world.std.com Layer of ash separates morning and evening milk. -----BEGIN PGP SIGNATURE----- Version: PGPfreeware 6.5.2 for non-commercial use http://www.pgp.com iQCVAwUBOuCi3WAMawgf2iXRAQHeAQQA3YSePSQ0XzdHZUVskFDkTfpE9XS4fHQs WaT6a8qLZK9PdNcoz3zggM/Jnjdx6CJqNzxPEtxk9B2DoGll/C/60HWNPN+VujDu Xav65S0P+Px4knaQcCIeCamQJ7uGcsw+CqMpNbxWYaTYmjAfkbKH1EuLC2VRwdmD wQmwrDp70v8= =8hLB -----END PGP SIGNATURE----- ------------=_4BF17E8E.BF8E0000--

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  • std::binary_function - no match for call?

    - by Venkat Shiva
    Hi, this is my code: #include <iostream> #include <functional> using namespace std; int main() { binary_function<double, double, double> operations[] = { plus<double>(), minus<double>(), multiplies<double>(), divides<double>() }; double a, b; int choice; cout << "Enter two numbers" << endl; cin >> a >> b; cout << "Enter opcode: 0-Add 1-Subtract 2-Multiply 3-Divide" << endl; cin >> choice; cout << operations[choice](a, b) << endl; } and the error I am getting is: Calcy.cpp: In function ‘int main()’: Calcy.cpp:17: error: no match for call to ‘(std::binary_function<double, double, double>) (double&, double&)’ Can anyone explain why I am getting this error and how to get rid of it?

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  • Actual long double precision does not agree with std::numeric_limits

    - by dmb
    Working on Mac OS X 10.6.2, Intel, with i686-apple-darwin10-g++-4.2.1, and compiling with the -arch x86_64 flag, I just noticed that while... std::numeric_limits<long double>::max_exponent10 = 4932 ...as is expected, when a long double is actually set to a value with exponent greater than 308, it becomes inf--ie in reality it only has 64bit precision instead of 80bit. Also, sizeof() is showing long doubles to be 16 bytes, which they should be. Finally, using gives the same results as . Does anyone know where the discrepancy might be? long double x = 1e308, y = 1e309; cout << std::numeric_limits::max_exponent10 << endl; cout << x << '\t' << y << endl; cout << sizeof(x) << endl; gives 4932 1e+308 inf 16

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  • Error trying to use rand from std library cstdlib with g++

    - by Matt
    I was trying to use the random function in Ubuntu compiling with g++ on a larger program and for some reason rand just gave weird compile errors. For testing purposes I made the simplest program I could and it still gives errors. Program: #include <iostream> using std::cout; using std::endl; #include <cstdlib> int main() { cout << "Random number " << rand(); return 0; } Error when compiling with the terminal sudo g++ chapter_3/tester.cpp ./test ./test: In function _start': /build/buildd/eglibc-2.10.1/csu/../sysdeps/i386/elf/start.S:65: multiple definition of_start' /usr/lib/gcc/i486-linux-gnu/4.4.1/../../../../lib/crt1.o:/build/buildd/eglibc-2.10.1/csu/../sysdeps/i386/elf/start.S:65: first defined here ./test:(.rodata+0x0): multiple definition of _fp_hw' /usr/lib/gcc/i486-linux-gnu/4.4.1/../../../../lib/crt1.o:(.rodata+0x0): first defined here ./test: In function_fini': (.fini+0x0): multiple definition of _fini' /usr/lib/gcc/i486-linux-gnu/4.4.1/../../../../lib/crti.o:(.fini+0x0): first defined here ./test:(.rodata+0x4): multiple definition of_IO_stdin_used' /usr/lib/gcc/i486-linux-gnu/4.4.1/../../../../lib/crt1.o:(.rodata.cst4+0x0): first defined here ./test: In function __data_start': (.data+0x0): multiple definition ofdata_start' /usr/lib/gcc/i486-linux-gnu/4.4.1/../../../../lib/crt1.o:(.data+0x0): first defined here ./test: In function __data_start': (.data+0x4): multiple definition of__dso_handle' /usr/lib/gcc/i486-linux-gnu/4.4.1/crtbegin.o:(.data+0x0): first defined here ./test: In function main': (.text+0xb4): multiple definition ofmain' /tmp/cceF0x0p.o:tester.cpp:(.text+0x0): first defined here ./test: In function _init': (.init+0x0): multiple definition ofinit' /usr/lib/gcc/i486-linux-gnu/4.4.1/../../../../lib/crti.o:(.init+0x0): first defined here /usr/lib/gcc/i486-linux-gnu/4.4.1/crtend.o:(.dtors+0x0): multiple definition of `_DTOR_END' ./test:(.dtors+0x4): first defined here /usr/bin/ld: error in ./test(.eh_frame); no .eh_frame_hdr table will be created. collect2: ld returned 1 exit status

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  • Normal pointer vs Auto pointer (std::auto_ptr)

    - by AKN
    Code snippet (normal pointer) int *pi = new int; int i = 90; pi = &i; int k = *pi + 10; cout<<k<<endl; delete pi; [Output: 100] Code snippet (auto pointer) Case 1: std::auto_ptr<int> pi(new int); int i = 90; pi = &i; int k = *pi + 10; //Throws unhandled exception error at this point while debugging. cout<<k<<endl; //delete pi; (It deletes by itself when goes out of scope. So explicit 'delete' call not required) Case 2: std::auto_ptr<int> pi(new int); int i = 90; *pi = 90; int k = *pi + 10; cout<<k<<endl; [Output: 100] Can someone please tell why it failed to work for case 1?

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  • std::stringstream GCC Abnormal Behavior

    - by FlorianZ
    I have a very interesting problem with compiling a short little program on a Mac (GCC 4.2). The function below would only stream chars or strings into the stringstream, but not anything else (int, double, float, etc.) In fact, the fail flag is set if I attempt to convert for example an int into a string. However, removing the preprocessor flag: _GLIBCXX_DEBUG=1, which is set by default in XCode for the debug mode, will yield the desired results / correct behavior. Here is the simple function I am talking about. value is template variable of type T. Tested for int, double, float (not working), char and strings (working). template < typename T > const std::string Attribute<T>::getValueAsString() const { std::ostringstream stringValue; stringValue << value; return stringValue.str(); } Any ideas what I am doing wrong, why this doesn't work, or what the preprocessor flag does to make this not work anymore? Thanks!

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  • Using boost::random to select from an std::list where elements are being removed

    - by user144182
    See this related question on more generic use of the Boost Random library. My questions involves selecting a random element from an std::list, doing some operation, which could potentally include removing the element from the list, and then choosing another random element, until some condition is satisfied. The boost code and for loop look roughly like this: // create and insert elements into list std::list<MyClass> myList; //[...] // select uniformly from list indices boost::uniform_int<> indices( 0, myList.size()-1 ); boost::variate_generator< boost::mt19937, boost::uniform_int<> > selectIndex(boost::mt19937(), indices); for( int i = 0; i <= maxOperations; ++i ) { int index = selectIndex(); MyClass & mc = myList.begin() + index; // do operations with mc, potentially removing it from myList //[...] } My problem is as soon as the operations that are performed on an element result in the removal of an element, the variate_generator has the potential to select an invalid index in the list. I don't think it makes sense to completely recreate the variate_generator each time, especially if I seed it with time(0).

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  • Difference between std::result_of and decltype

    - by Luc Touraille
    I have some trouble understanding the need for std::result_of in C++0x. If I understood correctly, result_of is used to obtain the resulting type of invoking a function object with certain types of parameters. For example: template <typename F, typename Arg> typename std::result_of<F(Arg)> invoke(F f, Arg a) { return f(a); } I don't really see the difference with the following code: template <typename F, typename Arg> auto invoke(F f, Arg a) -> decltype(f(a)) //uses the f parameter { return f(a); } or template <typename F, typename Arg> auto invoke(F f, Arg a) -> decltype(F()(a)); //"constructs" an F { return f(a); } The only problem I can see with these two solutions is that we need to either: have an instance of the functor to use it in the expression passed to decltype. know a defined constructor for the functor. Am I right in thinking that the only difference between decltype and result_of is that the first one needs an expression whereas the second does not?

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  • front end to linux std mailbox for development purposes

    - by Fabio
    I am actually a software developer, do have a fair amount of linux experience as a user though since 1997. I am normally on stackoverflow.com, please excuse me if this question isn't appropriate here. I am working on a web project. We send out emails. I work locally on a linux box. When coding I use my local mailboxes to check what's been sent. Emails sent out to valid email addresses are not arriving at my official mailbox; they might be stopped by the provider's mail servers (gmail, yahoo). Now, we are sending out HTML mails too. I need to check how they look like. Is there a GUI frontend to the standard linux BSD mailbox? Or should I install some IMAP/POP server for this? Will such server get the emails sent to username@localhost ? Thanks for any suggestion

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  • How to install virtio balloon driver in Windows Server 2008 Std x64

    - by javano
    I am trying to run the install command in the INF file that comes on the virtio drivers ISO, after having downloaded devcon.exe from Microsoft's website. I am getting the following error and I don't know how to progress; C:\Users\Administrator\Desktop\ADM64>devcon install BALLOON.inf PCI\VEN_1AF4&DEV_1002&SUBSYS_00051AF4&REV_00 devcon.exe failed. 'DEV_1002' is not recognized as an internal or external command, operable program or batch file. 'SUBSYS_00051AF4' is not recognized as an internal or external command, operable program or batch file. 'REV_00' is not recognized as an internal or external command, operable program or batch file. Thank you.

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  • upgrade from windows server 2008 r2 std to enterprise

    - by Ravi
    We recently had to upgrade our servers from Win 2008 R2 Standard to Enterprise. The upgrade method was DISM. After the upgrade, a lot of weird things started to happen. Though Windows says it's been properly activated, we lost 1) RDP settings (disappeared from the Remote Setting tab of Properties of My Computer) 2) The option to join a domain is grayed out 3) The server had to 2 physical processors 12 cores each. Now, task manager or windows sees only 1 processor (or only 12 cores) 4) the amount of physical ram on this sever is 32 GB (Windows reports only 4 GB are usable) Has anyone encountered this before ? Thanks Ravi

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  • 7zip: how to extract to std output?

    - by Jason S
    I have 7z 4.65 and am trying to extract a single file to standard output. The 7z command-line help says -so is the command-line parameter to extract to standard output, but when I try this: >>> 7z e -so dist\dlogpkg.jar META-INF/MANIFEST.MF 7-Zip 4.65 Copyright (c) 1999-2009 Igor Pavlov 2009-02-03 Error: I won't write data and program's messages to same terminal how can I fix this? There doesn't seem to be a command line param to suppress the normal 7z stdout messages. (edit: the equivalent operation in "unzip" would be unzip -p dist\dlogpkg.jar META-INF/MANIFEST.MF which works fine. But I'd like to use 7z for various reasons.)

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  • Windows 2003 X64 Std page file usage

    - by duhaas
    Just trying to understand why I'm seeing what I'm seeing on this system. Pagefile performance counters are telling me i'm @ about 1.5% used with my page file, settings for the file are 2GB-4GB, but task manager was showing 13GB usage: Oddly enough, it just sunk down: This machine has IBM DB2 9.5 workgroup edition running on it. Thoughts??? Actually, just learned the developer had just stopped DB2, hence the huge drop, just not understand the difference in the PF usage in task manager vs perf counters?

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  • STL operator= behavior change with Visual Studio 2010?

    - by augnob
    Hi, I am attempting to compile QtScriptGenerator (gitorious) with Visual Studio 2010 (C++) and have run into a compile error. In searching for a solution, I have seen occasional references to compile breakages introduced since VS2008 due to changes in VS2010's implementation of STL and/or c++0x conformance changes. Any ideas what is happening below, or how I could go about fixing it? If the offending code appeared to be QtScriptGenerator's, I think I would have an easier time fixing it.. but it appears to me that the offending code may be in VS2010's STL implementation and I may be required to create a workaround? PS. I am pretty unfamiliar with templates and STL. I have a background in embedded and console projects where such things have until recently often been avoided to reduce memory consumption and cross-compiler risks. C:\Program Files\Microsoft Visual Studio 10.0\VC\INCLUDE\xutility(275) : error C2679: binary '=' : no operator found which takes a right-hand operand of type 'rpp::pp_output_iterator<_Container>' (or there is no acceptable conversion) with [ _Container=std::string ] c:\qt\qtscriptgenerator\generator\parser\rpp\pp-iterator.h(75): could be 'rpp::pp_output_iterator<_Container> &rpp::pp_output_iterator<_Container>::operator =(const char &)' with [ _Container=std::string ] while trying to match the argument list '(rpp::pp_output_iterator<_Container>, rpp::pp_output_iterator<_Container>)' with [ _Container=std::string ] C:\Program Files\Microsoft Visual Studio 10.0\VC\INCLUDE\xutility(2176) : see reference to function template instantiation '_Iter &std::_Rechecked<_OutIt,_OutIt>(_Iter &,_UIter)' being compiled with [ _Iter=rpp::pp_output_iterator<std::string>, _OutIt=rpp::pp_output_iterator<std::string>, _UIter=rpp::pp_output_iterator<std::string> ] c:\qt\qtscriptgenerator\generator\parser\rpp\pp-internal.h(83) : see reference to function template instantiation '_OutIt std::copy<std::_String_iterator<_Elem,_Traits,_Alloc>,_OutputIterator>(_InIt,_InIt,_OutIt)' being compiled with [ _OutIt=rpp::pp_output_iterator<std::string>, _Elem=char, _Traits=std::char_traits<char>, _Alloc=std::allocator<char>, _OutputIterator=rpp::pp_output_iterator<std::string>, _InIt=std::_String_iterator<char,std::char_traits<char>,std::allocator<char>> ] c:\qt\qtscriptgenerator\generator\parser\rpp\pp-engine-bits.h(500) : see reference to function template instantiation 'void rpp::_PP_internal::output_line<_OutputIterator>(const std::string &,int,_OutputIterator)' being compiled with [ _OutputIterator=rpp::pp_output_iterator<std::string> ] C:\Program Files\Microsoft Visual Studio 10.0\VC\INCLUDE\xutility(275) : error C2582: 'operator =' function is unavailable in 'rpp::pp_output_iterator<_Container>' with [ _Container=std::string ] Here's some context.. pp-internal.h-- #ifndef PP_INTERNAL_H #define PP_INTERNAL_H #include <algorithm> #include <stdio.h> namespace rpp { namespace _PP_internal { .. 68 template <typename _OutputIterator> 69 void output_line(const std::string &__filename, int __line, _OutputIterator __result) 70 { 71 std::string __msg; 72 73 __msg += "# "; 74 75 char __line_descr[16]; 76 pp_snprintf (__line_descr, 16, "%d", __line); 77 __msg += __line_descr; 78 79 __msg += " \""; 80 81 if (__filename.empty ()) 82 __msg += "<internal>"; 83 else 84 __msg += __filename; 85 86 __msg += "\"\n"; 87 std::copy (__msg.begin (), __msg.end (), __result); 88 }

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  • dual map structure implementation?

    - by Danra
    Hey, I'm looking for a standard dual-map structure - is there one implemented in std/boost/another standard C++ library? When I say "dual-map" I mean a map which can be indexed efficiently both by the key and the "value" (it actually has two key types instead of one key type and one value type). for example: dualmap<int,string> m; m[1] = "foo"; m["bar"] = 2 int a = m["bar"]; // a = 2 Thanks, Dan

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  • Code runs 6 times slower with 2 threads than with 1

    - by Edward Bird
    So I have written some code to experiment with threads and do some testing. The code should create some numbers and then find the mean of those numbers. I think it is just easier to show you what I have so far. I was expecting with two threads that the code would run about 2 times as fast. Measuring it with a stopwatch I think it runs about 6 times slower! void findmean(std::vector<double>*, std::size_t, std::size_t, double*); int main(int argn, char** argv) { // Program entry point std::cout << "Generating data..." << std::endl; // Create a vector containing many variables std::vector<double> data; for(uint32_t i = 1; i <= 1024 * 1024 * 128; i ++) data.push_back(i); // Calculate mean using 1 core double mean = 0; std::cout << "Calculating mean, 1 Thread..." << std::endl; findmean(&data, 0, data.size(), &mean); mean /= (double)data.size(); // Print result std::cout << " Mean=" << mean << std::endl; // Repeat, using two threads std::vector<std::thread> thread; std::vector<double> result; result.push_back(0.0); result.push_back(0.0); std::cout << "Calculating mean, 2 Threads..." << std::endl; // Run threads uint32_t halfsize = data.size() / 2; uint32_t A = 0; uint32_t B, C, D; // Split the data into two blocks if(data.size() % 2 == 0) { B = C = D = halfsize; } else if(data.size() % 2 == 1) { B = C = halfsize; D = hsz + 1; } // Run with two threads thread.push_back(std::thread(findmean, &data, A, B, &(result[0]))); thread.push_back(std::thread(findmean, &data, C, D , &(result[1]))); // Join threads thread[0].join(); thread[1].join(); // Calculate result mean = result[0] + result[1]; mean /= (double)data.size(); // Print result std::cout << " Mean=" << mean << std::endl; // Return return EXIT_SUCCESS; } void findmean(std::vector<double>* datavec, std::size_t start, std::size_t length, double* result) { for(uint32_t i = 0; i < length; i ++) { *result += (*datavec).at(start + i); } } I don't think this code is exactly wonderful, if you could suggest ways of improving it then I would be grateful for that also.

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  • Getting template metaprogramming compile-time constants at runtime

    - by GMan - Save the Unicorns
    Background Consider the following: template <unsigned N> struct Fibonacci { enum { value = Fibonacci<N-1>::value + Fibonacci<N-2>::value }; }; template <> struct Fibonacci<1> { enum { value = 1 }; }; template <> struct Fibonacci<0> { enum { value = 0 }; }; This is a common example and we can get the value of a Fibonacci number as a compile-time constant: int main(void) { std::cout << "Fibonacci(15) = "; std::cout << Fibonacci<15>::value; std::cout << std::endl; } But you obviously cannot get the value at runtime: int main(void) { std::srand(static_cast<unsigned>(std::time(0))); // ensure the table exists up to a certain size // (even though the rest of the code won't work) static const unsigned fibbMax = 20; Fibonacci<fibbMax>::value; // get index into sequence unsigned fibb = std::rand() % fibbMax; std::cout << "Fibonacci(" << fibb << ") = "; std::cout << Fibonacci<fibb>::value; std::cout << std::endl; } Because fibb is not a compile-time constant. Question So my question is: What is the best way to peek into this table at run-time? The most obvious solution (and "solution" should be taken lightly), is to have a large switch statement: unsigned fibonacci(unsigned index) { switch (index) { case 0: return Fibonacci<0>::value; case 1: return Fibonacci<1>::value; case 2: return Fibonacci<2>::value; . . . case 20: return Fibonacci<20>::value; default: return fibonacci(index - 1) + fibonacci(index - 2); } } int main(void) { std::srand(static_cast<unsigned>(std::time(0))); static const unsigned fibbMax = 20; // get index into sequence unsigned fibb = std::rand() % fibbMax; std::cout << "Fibonacci(" << fibb << ") = "; std::cout << fibonacci(fibb); std::cout << std::endl; } But now the size of the table is very hard coded and it wouldn't be easy to expand it to say, 40. The only one I came up with that has a similiar method of query is this: template <int TableSize = 40> class FibonacciTable { public: enum { max = TableSize }; static unsigned get(unsigned index) { if (index == TableSize) { return Fibonacci<TableSize>::value; } else { // too far, pass downwards return FibonacciTable<TableSize - 1>::get(index); } } }; template <> class FibonacciTable<0> { public: enum { max = 0 }; static unsigned get(unsigned) { // doesn't matter, no where else to go. // must be 0, or the original value was // not in table return 0; } }; int main(void) { std::srand(static_cast<unsigned>(std::time(0))); // get index into sequence unsigned fibb = std::rand() % FibonacciTable<>::max; std::cout << "Fibonacci(" << fibb << ") = "; std::cout << FibonacciTable<>::get(fibb); std::cout << std::endl; } Which seems to work great. The only two problems I see are: Potentially large call stack, since calculating Fibonacci<2 requires we go through TableMax all the way to 2, and: If the value is outside of the table, it returns zero as opposed to calculating it. So is there something I am missing? It seems there should be a better way to pick out these values at runtime. A template metaprogramming version of a switch statement perhaps, that generates a switch statement up to a certain number? Thanks in advance.

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  • Using a boost::fusion::map in boost::spirit::karma

    - by user1097105
    I am using boost spirit to parse some text files into a data structure and now I am beginning to generate text from this data structure (using spirit karma). One attempt at a data structure is a boost::fusion::map (as suggested in an answer to this question). But although I can use boost::spirit::qi::parse() and get data in it easily, when I tried to generate text from it using karma, I failed. Below is my attempt (look especially at the "map_data" type). After some reading and playing around with other fusion types, I found boost::fusion::vector and BOOST_FUSION_DEFINE_ASSOC_STRUCT. I succeeded to generate output with both of them, but they don't seem ideal: in vector you cannot access a member using a name (it is like a tuple) -- and in the other solution, I don't think I need both ways (member name and key type) to access the members. #include <iostream> #include <string> #include <boost/spirit/include/karma.hpp> #include <boost/fusion/include/map.hpp> #include <boost/fusion/include/make_map.hpp> #include <boost/fusion/include/vector.hpp> #include <boost/fusion/include/as_vector.hpp> #include <boost/fusion/include/transform.hpp> struct sb_key; struct id_key; using boost::fusion::pair; typedef boost::fusion::map < pair<sb_key, int> , pair<id_key, unsigned long> > map_data; typedef boost::fusion::vector < int, unsigned long > vector_data; #include <boost/fusion/include/define_assoc_struct.hpp> BOOST_FUSION_DEFINE_ASSOC_STRUCT( (), assocstruct_data, (int, a, sb_key) (unsigned long, b, id_key)) namespace karma = boost::spirit::karma; template <typename X> std::string to_string ( const X& data ) { std::string generated; std::back_insert_iterator<std::string> sink(generated); karma::generate_delimited ( sink, karma::int_ << karma::ulong_, karma::space, data ); return generated; } int main() { map_data d1(boost::fusion::make_map<sb_key, id_key>(234, 35314988526ul)); vector_data d2(boost::fusion::make_vector(234, 35314988526ul)); assocstruct_data d3(234,35314988526ul); std::cout << "map_data as_vector: " << boost::fusion::as_vector(d1) << std::endl; //std::cout << "map_data to_string: " << to_string(d1) << std::endl; //*FAIL No 1* std::cout << "at_key (sb_key): " << boost::fusion::at_key<sb_key>(d1) << boost::fusion::at_c<0>(d1) << std::endl << std::endl; std::cout << "vector_data: " << d2 << std::endl; std::cout << "vector_data to_string: " << to_string(d2) << std::endl << std::endl; std::cout << "assoc_struct as_vector: " << boost::fusion::as_vector(d3) << std::endl; std::cout << "assoc_struct to_string: " << to_string(d3) << std::endl; std::cout << "at_key (sb_key): " << boost::fusion::at_key<sb_key>(d3) << d3.a << boost::fusion::at_c<0>(d3) << std::endl; return 0; } Including the commented line gives lots of pages of compilation errors, among which notably something like: no known conversion for argument 1 from ‘boost::fusion::pair’ to ‘double’ no known conversion for argument 1 from ‘boost::fusion::pair’ to ‘float’ Might it be that to_string needs the values of the map_data, and not the pairs? Though I am not good with templates, I tried to get a vector from a map using transform in the following way template <typename P> struct take_second { typename P::second_type operator() (P p) { return p.second; } }; // ... inside main() pair <char, int> ff(32); std::cout << "take_second (expect 32): " << take_second<pair<char,int>>()(ff) << std::endl; std::cout << "transform map_data and to_string: " << to_string(boost::fusion::transform(d1, take_second<>())); //*FAIL No 2* But I don't know what types am I supposed to give when instantiating take_second and anyway I think there must be an easier way to get (iterate over) the values of a map (is there?) If you answer this question, please also give your opinion on whether using an ASSOC_STRUCT or a map is better.

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  • what to use in place of std::map::emplace?

    - by kfmfe04
    For containers such as std::map< std::string, std::unique_ptr< Foo >>, it looks like emplace() has yet to be implemented in stdc++ as of gcc 4.7.2. Unfortunately, I can't store Foo directly by value as it is an abstract super-class. As a simple, but inefficient, place-holder, I've just been using std::map< std::string, Foo* > in conjunction with a std::vector< std::unique_ptr< Foo >> for garbage collection. Do you have a interim solution that is more efficient and more easily replaced once emplace() is available?

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  • Objective C -std=c99 usage

    - by Andy White
    Is there any reason why you shouldn't use the "-std=c99" flag for compiling Objective-C programs on Mac? The one feature in C99 that I really like is the ability to declare variables anywhere in code, rather than just at the top of methods, but does this flag causes any problems or create incompatibilities for iPhone or Cocoa apps?

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  • Is it worth using std::tr1 in production?

    - by flashnik
    I'm using MS VC 2008 and for some projects Intel C++ compiler 11.0. Is it worth using tr1 features in production? Will they stay in new standard? For example, now I use stdext::hash_map. TR1 defines std::tr1::unordered_map. But in MS implementation unordered_map is just theirs stdext::hash_map, templatized in another way.

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  • std::string x(x);

    - by FredOverflow
    std::string x(x); This crashes very badly on my compiler. Does this mean I should test for this != &that in my own copy constructors, or can I assume that no client will ever be so stupid?

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