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• std::string.resize() and std::string.length()

  - by dreamlax

  I'm relatively new to C++ and I'm still getting to grips with the C++ Standard Library. To help transition from C, I want to format a std::string using printf-style formatters. I realise stringstream is a more type-safe approach, but I find myself finding printf-style much easier to read and deal with (at least, for the time being). This is my function: using namespace std; string formatStdString(const string &format, ...) { va_list va; string output; size_t needed; size_t used; va_start(va, format); needed = vsnprintf(&output[0], 0, format.c_str(), va); output.resize(needed + 1); // for null terminator?? used = vsnprintf(&output[0], output.capacity(), format.c_str(), va); // assert(used == needed); va_end(va); return output; } This works, kinda. A few things that I am not sure about are: Do I need to make room for a null terminator, or is this unnecessary? Is capacity() the right function to call here? I keep thinking length() would return 0 since the first character in the string is a '\0'. Occasionally while writing this string's contents to a socket (using its c_str() and length()), I have null bytes popping up on the receiving end, which is causing a bit of grief, but they seem to appear inconsistently. If I don't use this function at all, no null bytes appear.

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• Using std::ifstream to load in an array of struct data type into a std::vector

  - by Sent1nel

  I am working on a bitmap loader in C++ and when moving from the C style array to the std::vector I have run into an usual problem of which Google does not seem to have the answer. 8 Bit and 4 bit, bitmaps contain a colour palette. The colour palette has blue, green, red and reserved components each 1 byte in size. // Colour palette struct BGRQuad { UInt8 blue; UInt8 green; UInt8 red; UInt8 reserved; }; The problem I am having is when I create a vector of the BGRQuad structure I can no longer use the ifstream read function to load data from the file directly into the BGRQuad vector. // This code throws an assert failure! std::vecotr quads; if (coloursUsed) // colour table available { // read in the colours quads.reserve(coloursUsed); inFile.read( reinterpret_cast(&quads[0]), coloursUsed * sizeof(BGRQuad) ); } Does anyone know how to read directly into the vector without having to create a C array and copy data into the BGRQuad vector?

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• On reference_wrapper and callable objects

  - by Nicola Bonelli

  Given the following callable object: struct callable : public std::unary_function &lt;void, void&gt; { void operator()() const { std::cout << "hello world" << std::endl; } }; a std::tr1::reference_wrapper< calls through it: callable obj; std::tr1::ref(obj)(); Instead, when the operator() accepts an argument: struct callable : public std::unary_function &lt;int, void&gt; { void operator()(int n) const { std::cout << n << std::endl; } }; std::tr1::bind accepts a reference_wrapper to it as a callable wrapper... callable obj; std::tr1::bind( std::tr1::ref(obj), 42 )(); but what's wrong with this? std::tr1::ref(obj)(42);

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• Making uppercase of std::string

  - by Daniel K.

  Which implementation do you think is better? std::string ToUpper( const std::string& source ) { std::string result; result.reserve( source.length() ); std::transform( source.begin(), source.end(), result.begin(), std::ptr_fun<int, int>( std::toupper ) ); return result; } and... std::string ToUpper( const std::string& source ) { std::string result( source.length(), '\0' ); std::transform( source.begin(), source.end(), result.begin(), std::ptr_fun<int, int>( std::toupper ) ); return result; } Difference is that the first one uses reserve method after the default constructor, but the second one uses the constructor accepting the number of characters.

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• Specializing function template for both std::string and char*

  - by sad_man

  As the title says I want to specialize a function template for both string and char pointer, so far I did this but I can not figure out passing the string parameters by reference. #include <iostream> #include <string> template<typename T> void xxx(T param) { std::cout << "General : "<< sizeof(T) << std::endl; } template<> void xxx<char*>(char* param) { std::cout << "Char ptr: "<< strlen(param) << std::endl; } template<> void xxx<const char* >(const char* param) { std::cout << "Const Char ptr : "<< strlen(param)<< std::endl; } template<> void xxx<const std::string & >(const std::string & param) { std::cout << "Const String : "<< param.size()<< std::endl; } template<> void xxx<std::string >(std::string param) { std::cout << "String : "<< param.size()<< std::endl; } int main() { xxx("word"); std::string aword("word"); xxx(aword); std::string const cword("const word"); xxx(cword); } Also template<> void xxx<const std::string & >(const std::string & param) thing just does not working. If I rearranged the opriginal template to accept parameters as T& then the char * is required to be char * & which is not good for static text in code. Please help !

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• How to fix Ogre3d segfault with std::_Rb_tree_insert_and_rebalance ?

  - by Balázs Béla

  Hello all. I'm working on a 3d music visualizer using Ogre3d, basically it's a spectrum analizer, a lot like the old xmms plugin: (http)://www.youtube.com/watch?v=_6NKBiwYN24 It works well, the bars are drawn and updated, there are no framerate issues, but it crashes randomly. Sometimes it can run without problems, finish the song, other times it crashes instantly, other times the music just stops, without a crash. Here is the source code for the main class : https://github.com/balazsbela/OgreVisualizer/blob/master/src/VisualizerApplication.cpp#L221 Also the crashes seem to happen less often when I display the framerate overlay from Ogre samples. Would limiting the framerate help ? The crashes are seemingly random. Is it a performance issue ? Please help me out, I'm quite lost on this one, I also posted on Ogre3d forums but I received no responses. (http)://www.ogre3d.org/forums/viewtopic.php?f=2&t=63207 I also tried stackoverflow: (http)://stackoverflow.com/questions/5050147/how-to-fix-ogre3d-segfault-with-std-rb-tree-insert-and-rebalance Thank you. Backtrace: balazsbela@darknet:~/workspace/OgreVisualizer/Release$ gdb OgreVisualizer core GNU gdb (GDB) 7.2-debian Copyright (C) 2010 Free Software Foundation, Inc. License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html> This is free software: you are free to change and redistribute it. There is NO WARRANTY, to the extent permitted by law. Type "show copying" and "show warranty" for details. This GDB was configured as "i486-linux-gnu". For bug reporting instructions, please see: <http://www.gnu.org/software/gdb/bugs/>... Reading symbols from /home/balazsbela/workspace/OgreVisualizer/Release/OgreVisualizer...done. [New Thread 17705] [New Thread 17702] [New Thread 17703] [New Thread 17700] Reading symbols from /usr/lib/libv4l/v4l1compat.so...(no debugging symbols found)...done. Loaded symbols for /usr/lib/libv4l/v4l1compat.so Reading symbols from /usr/local/lib/libOgreMain.so.1.7.1...done. Loaded symbols for /usr/local/lib/libOgreMain.so.1.7.1 Reading symbols from /usr/lib/libfftw3.so.3...(no debugging symbols found)...done. Loaded symbols for /usr/lib/libfftw3.so.3 Reading symbols from /usr/lib/libSDL_sound-1.0.so.1...(no debugging symbols found)...done. Loaded symbols for /usr/lib/libSDL_sound-1.0.so.1 Reading symbols from /usr/lib/libSDL-1.2.so.0...(no debugging symbols found)...done. Loaded symbols for /usr/lib/libSDL-1.2.so.0 Reading symbols from /usr/lib/libSDL_mixer-1.2.so.0...(no debugging symbols found)...done. Loaded symbols for /usr/lib/libSDL_mixer-1.2.so.0 Reading symbols from /usr/lib/libOIS-1.2.0.so...(no debugging symbols found)...done. Loaded symbols for /usr/lib/libOIS-1.2.0.so Reading symbols from /usr/lib/libstdc++.so.6...(no debugging symbols found)...done. Loaded symbols for /usr/lib/libstdc++.so.6 Reading symbols from /lib/i686/cmov/libm.so.6...Reading symbols from /usr/lib/debug/lib/i686/cmov/libm-2.11.2.so...done. done. Loaded symbols for /lib/i686/cmov/libm.so.6 Reading symbols from /lib/libgcc_s.so.1...(no debugging symbols found)...done. Loaded symbols for /lib/libgcc_s.so.1 Reading symbols from /lib/i686/cmov/libc.so.6...Reading symbols from /usr/lib/debug/lib/i686/cmov/libc-2.11.2.so...done. done. Loaded symbols for /lib/i686/cmov/libc.so.6 Reading symbols from /lib/i686/cmov/libpthread.so.0...Reading symbols from /usr/lib/debug/lib/i686/cmov/libpthread-2.11.2.so...done. done. Loaded symbols for /lib/i686/cmov/libpthread.so.0 Reading symbols from /usr/local/lib/libv4l1.so.0...done. Loaded symbols for /usr/local/lib/libv4l1.so.0 Reading symbols from /usr/lib/libfreetype.so.6...(no debugging symbols found)...done. Loaded symbols for /usr/lib/libfreetype.so.6 Reading symbols from /usr/lib/libSM.so.6...(no debugging symbols found)...done. Loaded symbols for /usr/lib/libSM.so.6 Reading symbols from /usr/lib/libICE.so.6...(no debugging symbols found)...done. Loaded symbols for /usr/lib/libICE.so.6 Reading symbols from /usr/lib/libX11.so.6...(no debugging symbols found)...done. Loaded symbols for /usr/lib/libX11.so.6 Reading symbols from /usr/lib/libXext.so.6...(no debugging symbols found)...done. Loaded symbols for /usr/lib/libXext.so.6 Reading symbols from /usr/lib/libXt.so.6...(no debugging symbols found)...done. Loaded symbols for /usr/lib/libXt.so.6 Reading symbols from /usr/lib/libXaw.so.7...(no debugging symbols found)...done. Loaded symbols for /usr/lib/libXaw.so.7 Reading symbols from /lib/i686/cmov/libdl.so.2...Reading symbols from /usr/lib/debug/lib/i686/cmov/libdl-2.11.2.so...done. done. Loaded symbols for /lib/i686/cmov/libdl.so.2 Reading symbols from /usr/lib/libboost_thread.so.1.42.0...(no debugging symbols found)...done. Loaded symbols for /usr/lib/libboost_thread.so.1.42.0 Reading symbols from /usr/lib/libboost_date_time.so.1.42.0...(no debugging symbols found)...done. Loaded symbols for /usr/lib/libboost_date_time.so.1.42.0 Reading symbols from /usr/lib/libfreeimage.so.3...(no debugging symbols found)...done. Loaded symbols for /usr/lib/libfreeimage.so.3 Reading symbols from /usr/lib/libzzip-0.so.13...(no debugging symbols found)...done. Loaded symbols for /usr/lib/libzzip-0.so.13 Reading symbols from /usr/lib/libz.so.1...(no debugging symbols found)...done. Loaded symbols for /usr/lib/libz.so.1 Reading symbols from /usr/lib/libsmpeg-0.4.so.0...(no debugging symbols found)...done. Loaded symbols for /usr/lib/libsmpeg-0.4.so.0 Reading symbols from /usr/lib/libmikmod.so.2...(no debugging symbols found)...done. Loaded symbols for /usr/lib/libmikmod.so.2 Reading symbols from /usr/lib/libvorbis.so.0...(no debugging symbols found)...done. Loaded symbols for /usr/lib/libvorbis.so.0 Reading symbols from /usr/lib/libvorbisfile.so.3...(no debugging symbols found)...done. Loaded symbols for /usr/lib/libvorbisfile.so.3 Reading symbols from /usr/lib/libFLAC.so.8...(no debugging symbols found)...done. Loaded symbols for /usr/lib/libFLAC.so.8 Reading symbols from /usr/lib/libogg.so.0...(no debugging symbols found)...done. Loaded symbols for /usr/lib/libogg.so.0 Reading symbols from /usr/lib/sse2/libspeex.so.1...(no debugging symbols found)...done. Loaded symbols for /usr/lib/sse2/libspeex.so.1 Reading symbols from /usr/lib/libasound.so.2...(no debugging symbols found)...done. Loaded symbols for /usr/lib/libasound.so.2 Reading symbols from /lib/i686/cmov/librt.so.1...Reading symbols from /usr/lib/debug/lib/i686/cmov/librt-2.11.2.so...done. done. Loaded symbols for /lib/i686/cmov/librt.so.1 Reading symbols from /usr/lib/libdirectfb-1.2.so.9...(no debugging symbols found)...done. Loaded symbols for /usr/lib/libdirectfb-1.2.so.9 Reading symbols from /usr/lib/libfusion-1.2.so.9...(no debugging symbols found)...done. Loaded symbols for /usr/lib/libfusion-1.2.so.9 Reading symbols from /usr/lib/libdirect-1.2.so.9...(no debugging symbols found)...done. Loaded symbols for /usr/lib/libdirect-1.2.so.9 Reading symbols from /usr/lib/libvga.so.1...(no debugging symbols found)...done. Loaded symbols for /usr/lib/libvga.so.1 Reading symbols from /lib/ld-linux.so.2...Reading symbols from /usr/lib/debug/lib/ld-2.11.2.so...done. done. Loaded symbols for /lib/ld-linux.so.2 Reading symbols from /usr/local/lib/libv4l2.so.0...done. Loaded symbols for /usr/local/lib/libv4l2.so.0 Reading symbols from /lib/libuuid.so.1...(no debugging symbols found)...done. Loaded symbols for /lib/libuuid.so.1 Reading symbols from /usr/lib/libxcb.so.1...(no debugging symbols found)...done. Loaded symbols for /usr/lib/libxcb.so.1 Reading symbols from /usr/lib/libXmu.so.6...(no debugging symbols found)...done. Loaded symbols for /usr/lib/libXmu.so.6 Reading symbols from /usr/lib/libXpm.so.4...(no debugging symbols found)...done. Loaded symbols for /usr/lib/libXpm.so.4 Reading symbols from /usr/lib/libjpeg.so.62...(no debugging symbols found)...done. Loaded symbols for /usr/lib/libjpeg.so.62 Reading symbols from /usr/lib/libmng.so.1...(no debugging symbols found)...done. Loaded symbols for /usr/lib/libmng.so.1 Reading symbols from /usr/lib/libopenjpeg.so.2...(no debugging symbols found)...done. Loaded symbols for /usr/lib/libopenjpeg.so.2 Reading symbols from /lib/libpng12.so.0...(no debugging symbols found)...done. Loaded symbols for /lib/libpng12.so.0 Reading symbols from /usr/lib/libIlmImf.so.6...(no debugging symbols found)...done. Loaded symbols for /usr/lib/libIlmImf.so.6 Reading symbols from /usr/lib/libImath.so.6...(no debugging symbols found)...done. Loaded symbols for /usr/lib/libImath.so.6 Reading symbols from /usr/lib/libHalf.so.6...(no debugging symbols found)...done. Loaded symbols for /usr/lib/libHalf.so.6 Reading symbols from /usr/lib/libIex.so.6...(no debugging symbols found)...done. Loaded symbols for /usr/lib/libIex.so.6 Reading symbols from /usr/lib/libIlmThread.so.6...(no debugging symbols found)...done. Loaded symbols for /usr/lib/libIlmThread.so.6 Reading symbols from /lib/libx86.so.1...(no debugging symbols found)...done. Loaded symbols for /lib/libx86.so.1 Reading symbols from /usr/local/lib/libv4lconvert.so.0...done. Loaded symbols for /usr/local/lib/libv4lconvert.so.0 Reading symbols from /usr/lib/libXau.so.6...(no debugging symbols found)...done. Loaded symbols for /usr/lib/libXau.so.6 Reading symbols from /usr/lib/libXdmcp.so.6...(no debugging symbols found)...done. Loaded symbols for /usr/lib/libXdmcp.so.6 Reading symbols from /usr/lib/liblcms.so.1...(no debugging symbols found)...done. Loaded symbols for /usr/lib/liblcms.so.1 Reading symbols from /usr/local/lib/OGRE/RenderSystem_GL.so...done. Loaded symbols for /usr/local/lib/OGRE/RenderSystem_GL.so Reading symbols from /usr/lib/libGLU.so.1...(no debugging symbols found)...done. Loaded symbols for /usr/lib/libGLU.so.1 Reading symbols from /usr/lib/libGL.so.1...(no debugging symbols found)...done. Loaded symbols for /usr/lib/libGL.so.1 Reading symbols from /usr/lib/libXrandr.so.2...(no debugging symbols found)...done. Loaded symbols for /usr/lib/libXrandr.so.2 Reading symbols from /usr/lib/libGLcore.so.1...(no debugging symbols found)...done. Loaded symbols for /usr/lib/libGLcore.so.1 Reading symbols from /usr/lib/tls/libnvidia-tls.so.1...(no debugging symbols found)...done. Loaded symbols for /usr/lib/tls/libnvidia-tls.so.1 Reading symbols from /usr/lib/libXrender.so.1...(no debugging symbols found)...done. Loaded symbols for /usr/lib/libXrender.so.1 Reading symbols from /usr/lib/libXcursor.so.1...(no debugging symbols found)...done. Loaded symbols for /usr/lib/libXcursor.so.1 Reading symbols from /usr/lib/libXfixes.so.3...(no debugging symbols found)...done. Loaded symbols for /usr/lib/libXfixes.so.3 Reading symbols from /lib/i686/cmov/libnss_compat.so.2...Reading symbols from /usr/lib/debug/lib/i686/cmov/libnss_compat-2.11.2.so...done. done. Loaded symbols for /lib/i686/cmov/libnss_compat.so.2 Reading symbols from /lib/i686/cmov/libnsl.so.1...Reading symbols from /usr/lib/debug/lib/i686/cmov/libnsl-2.11.2.so...done. done. Loaded symbols for /lib/i686/cmov/libnsl.so.1 Reading symbols from /lib/i686/cmov/libnss_nis.so.2...Reading symbols from /usr/lib/debug/lib/i686/cmov/libnss_nis-2.11.2.so...done. done. Loaded symbols for /lib/i686/cmov/libnss_nis.so.2 Reading symbols from /lib/i686/cmov/libnss_files.so.2...Reading symbols from /usr/lib/debug/lib/i686/cmov/libnss_files-2.11.2.so...done. done. Loaded symbols for /lib/i686/cmov/libnss_files.so.2 Reading symbols from /usr/lib/alsa-lib/libasound_module_rate_speexrate.so...(no debugging symbols found)...done. Loaded symbols for /usr/lib/alsa-lib/libasound_module_rate_speexrate.so Reading symbols from /usr/lib/sse2/libspeexdsp.so.1...(no debugging symbols found)...done. Loaded symbols for /usr/lib/sse2/libspeexdsp.so.1 Core was generated by `./OgreVisualizer'. Program terminated with signal 11, Segmentation fault. #0 0xb6dc563d in std::_Rb_tree_insert_and_rebalance(bool, std::_Rb_tree_node_base*, std::_Rb_tree_node_base*, std::_Rb_tree_node_base&) () from /usr/lib/libstdc++.so.6 (gdb) bt #0 0xb6dc563d in std::_Rb_tree_insert_and_rebalance(bool, std::_Rb_tree_node_base*, std::_Rb_tree_node_base*, std::_Rb_tree_node_base&) () from /usr/lib/libstdc++.so.6 #1 0xb73bb3c2 in std::_Rb_tree<Ogre::Node*, Ogre::Node*, std::_Identity<Ogre::Node*>, std::less<Ogre::Node*>, Ogre::STLAllocator<Ogre::Node*, Ogre::CategorisedAllocPolicy<(Ogre::MemoryCategory)0> > >::_M_insert_(std::_Rb_tree_node_base const*, std::_Rb_tree_node_base const*, Ogre::Node* const&) () from /usr/local/lib/libOgreMain.so.1.7.1 #2 0xb73b5a52 in _M_insert_unique (this=0xb6157ea0, child=0xb616aff8, forceParentUpdate=false) at /usr/include/c++/4.4/bits/stl_tree.h:1182 #3 insert (this=0xb6157ea0, child=0xb616aff8, forceParentUpdate=false) at /usr/include/c++/4.4/bits/stl_set.h:411 #4 Ogre::Node::requestUpdate (this=0xb6157ea0, child=0xb616aff8, forceParentUpdate=false) at /home/balazsbela/Downloads/ogre_src_v1-7-1/OgreMain/src/OgreNode.cpp:805 #5 0xb73b6a40 in Ogre::Node::needUpdate (this=0xb616aff8, forceParentUpdate=92) at /home/balazsbela/Downloads/ogre_src_v1-7-1/OgreMain/src/OgreNode.cpp:789 #6 0xb73b5038 in Ogre::Node::setScale (this=0x1825c, scale=...) at /home/balazsbela/Downloads/ogre_src_v1-7-1/OgreMain/src/OgreNode.cpp:638 #7 0x0805d306 in VisualizerApplication::adjustNodes (this=0x9cd4808) at ../src/VisualizerApplication.cpp:236 #8 0xb6e867f0 in ?? () from /usr/lib/libSDL_mixer-1.2.so.0 #9 0xb6e8719a in ?? () from /usr/lib/libSDL_mixer-1.2.so.0 #10 0xb6ed9b0d in ?? () from /usr/lib/libSDL-1.2.so.0 #11 0xb6ee185e in ?? () from /usr/lib/libSDL-1.2.so.0 #12 0xb6f2e0bd in ?? () from /usr/lib/libSDL-1.2.so.0 #13 0xb6bc7955 in start_thread (arg=0xb198ab70) at pthread_create.c:300 #14 0xb6ca6e7e in clone () at ../sysdeps/unix/sysv/linux/i386/clone.S:130 (gdb) Ogre.log: (http)://pastie.org/1581790

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• C++ 'using': Should I use it or should I avoid it?

  - by Mehrdad

  I realize there are subtly different semantics for some of these, because of ADL. In general, though: Which one should I prefer (if any), and why? (Or does it depend on the situation (e.g. inline header vs. implementation?) Also: should I prefer ::std:: over std::? using namespace std; pair<string::const_iterator, string::const_iterator> f(const string &s) { return make_pair(s.begin(), s.end()); } or std::pair<std::string::const_iterator, std::string::const_iterator> f(const std::string &s) { return std::make_pair(s.begin(), s.end()); } or using std::pair; using std::string; pair<string::const_iterator, string::const_iterator> f(const string &s) { return make_pair(s.begin(), s.end()); } or std::pair<std::string::const_iterator, std::string::const_iterator> f(const std::string &s) { using std::make_pair; return make_pair(s.begin(), s.end()); } or std::pair<std::string::const_iterator, std::string::const_iterator> f(const std::string &s) { using namespace std; return make_pair(s.begin(), s.end()); } or something else? (This is assuming I don't have C++11 and auto.)

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• issue with std::advance on std::sets

  - by tim

  I've stumbled upon what I believe is a bug in the stl algorithm advance. When I'm advancing the iterator off of the end of the container, I get inconsistent results. Sometimes I get container.end(), sometimes I get the last element. I've illustrated this with the following code: #include <algorithm> #include <cstdio> #include <set> using namespace std; typedef set<int> tMap; int main(int argc, char** argv) { tMap::iterator i; tMap the_map; for (int i=0; i<10; i++) the_map.insert(i); #if EXPERIMENT==1 i = the_map.begin(); #elif EXPERIMENT==2 i = the_map.find(4); #elif EXPERIMENT==3 i = the_map.find(5); #elif EXPERIMENT==4 i = the_map.find(6); #elif EXPERIMENT==5 i = the_map.find(9); #elif EXPERIMENT==6 i = the_map.find(2000); #else i = the_map.end(); #endif advance(i, 100); if (i == the_map.end()) printf("the end\n"); else printf("wuh? %d\n", *i); return 0; } Which I get the following unexpected (according to me) behavior in experiment 3 and 5 where I get the last element instead of the_map.end(). [tim@saturn advance]$ uname -srvmpio Linux 2.6.18-1.2798.fc6 #1 SMP Mon Oct 16 14:37:32 EDT 2006 i686 athlon i386 GNU/Linux [tim@saturn advance]$ g++ --version g++ (GCC) 4.1.1 20061011 (Red Hat 4.1.1-30) Copyright (C) 2006 Free Software Foundation, Inc. This is free software; see the source for copying conditions. There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. [tim@saturn advance]$ g++ -DEXPERIMENT=1 advance.cc [tim@saturn advance]$ ./a.out the end [tim@saturn advance]$ g++ -DEXPERIMENT=2 advance.cc [tim@saturn advance]$ ./a.out the end [tim@saturn advance]$ g++ -DEXPERIMENT=3 advance.cc [tim@saturn advance]$ ./a.out wuh? 9 [tim@saturn advance]$ g++ -DEXPERIMENT=4 advance.cc [tim@saturn advance]$ ./a.out the end [tim@saturn advance]$ g++ -DEXPERIMENT=5 advance.cc [tim@saturn advance]$ ./a.out wuh? 9 [tim@saturn advance]$ g++ -DEXPERIMENT=6 advance.cc [tim@saturn advance]$ ./a.out the end [tim@saturn advance]$ g++ -DEXPERIMENT=7 advance.cc [tim@saturn advance]$ ./a.out the end [tim@saturn advance]$ From the sgi website (see link at top), it has the following example: list<int> L; L.push_back(0); L.push_back(1); list<int>::iterator i = L.begin(); advance(i, 2); assert(i == L.end()); I would think that the assertion should apply to other container types, no? What am I missing? Thanks!

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• operator<< cannot output std::endl -- Fix?

  - by dehmann

  The following code gives an error when it's supposed to output just std::endl: #include <iostream> #include <sstream> struct MyStream { std::ostream* out_; MyStream(std::ostream* out) : out_(out) {} std::ostream& operator<<(const std::string& s) { (*out_) << s; return *out_; } }; template<class OutputStream> struct Foo { OutputStream* out_; Foo(OutputStream* out) : out_(out) {} void test() { (*out_) << "OK" << std::endl; (*out_) << std::endl; // ERROR } }; int main(int argc, char** argv){ MyStream out(&std::cout); Foo<MyStream> foo(&out); foo.test(); return EXIT_SUCCESS; } The error is: stream1.cpp:19: error: no match for 'operator<<' in '*((Foo<MyStream>*)this)->Foo<MyStream>::out_ << std::endl' stream1.cpp:7: note: candidates are: std::ostream& MyStream::operator<<(const std::string&) So it can output a string (see line above the error), but not just the std::endl, presumably because std::endl is not a string, but the operator<< definition asks for a string. Templating the operator<< didn't help: template<class T> std::ostream& operator<<(const T& s) { ... } How can I make the code work? Thanks!

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• How do I change java logging console output from std err to std out

  - by Obediah Stane

  I'm using the standard logger from java.util.logging and by default the console output is directed to the error stream (i.e. same as System.err.println). How do I change the console output to the output stream (i.e. same as System.out.println)

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• Insert an element to std::set using constructor

  - by Dave17

  is it possible to insert a new element to std::set like in case of std::list for example: //insert one element named "string" to sublist of mylist std::list< std::list<string> > mylist; mylist.push_back(std::list<string>(1, "string")); Now, mylist has one element of type std::string in its sub-list of type std::list. How can you do the same in if std::set is the sub-set of std::list my list i.e std::list<std::set <string>> mylist; if you can't then why not?

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• Confused about std::runtime_error vs. std::logic_error

  - by David Gladfelter

  I recently saw that the boost program_options library throws a logic_error if the command-line input was un-parsable. That challenged my assumptions about logic_error vs. runtime_error. I assumed that logic errors (logic_error and its derived classes) were problems that resulted from internal failures to adhere to program invariants, often in the form of illegal arguments to internal API's. In that sense they are largely equivalent to ASSERT's, but meant to be used in released code (unlike ASSERT's which are not usually compiled into released code.) They are useful in situations where it is infeasible to integrate separate software components in debug/test builds or the consequences of a failure are such that it is important to give runtime feedback about the invalid invariant condition to the user. Similarly, I thought that runtime_errors resulted exclusively from runtime conditions outside of the control of the programmer: I/O errors, invalid user input, etc. However, program_options is obviously heavily (primarily?) used as a means of parsing end-user input, so under my mental model it certainly should throw a runtime_error in the case of bad input. Where am I going wrong? Do you agree with the boost model of exception typing?

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• Why is 'using namespace std;' considered a bad practice in C++?

  - by Mana

  Okay, sorry for the simplistic question, but this has been bugging me ever since I finished high school C++ last year. I've been told by others on numerous occasions that my teacher was wrong in saying that we should have "using namespace std;" in our programs, and that std::cout and std::cin are more proper. However, they would always be vague as to why this is a bad practice. So, I'm asking now: Why is "using namespace std;" considered bad? Is it really that inefficient, or risk declaring ambiguous vars(variables that share the same name as a function in std namespace) that much? Or does this impact program performance noticeably as you get into writing larger applications? I'm sorry if this is something I should have googled to solve; I figured it would be nice to have this question on here regardless in case anyone else was wondering.

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• C++ find multiple keys from a std::multimap

  - by sch0ck9

  I have a STL::multimap and I search to populate a std::list with value which key is duplicated. Can I find/insert to a std::list the value of elements for all key where count 1 without counting them one by one? std::multimap<int, std::string> mm ; mm[0] = "a" ; mm[1] = "b" ; mm[0] = "c" ; mm[2] = "j" ; mm[2] = "k" ; std::list<std::string> lst ; lst might contains "a" ,"c","j","k" ; I try this template <class K, class V> class extract_value { private: K last_key_ ; std::list<V> m_list_value ; std::pair<K, V> first_elem ; public: extract_value(const K& k_): last_key_(k_) { } void operator() (std::pair<const K, V> elem) { if (last_key_ == elem.first) { m_list_value.push_back(elem.second) ; } else { // First entry last_key_ = elem.first; first_elem= elem ; } } std::list<V> get_value() { return m_list_value ; } }; ex_ = for_each(mm.begin(),mm.end(), extract_value<int, std::string>(0)) ; std::list<std::string> lst = ex_.get_value() ; I'm not sure that this code compile.

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• Makefile : Build in a separate directory tree

  - by Simone Margaritelli

  My project (an interpreted language) has a standard library composed by multiple files, each of them will be built into an .so dynamic library that the interpreter will load upon user request (with an import directive). Each source file is located into a subdirectory representing its "namespace", for instance : The build process has to create a "build" directory, then when each file is compiling has to create its namespace directory inside the "build" one, for instance, when compiling std/io/network/tcp.cc he run an mkdir command with mkdir -p build/std/io/network The Makefile snippet is : STDSRC=stdlib/std/hashing/md5.cc \ stdlib/std/hashing/crc32.cc \ stdlib/std/hashing/sha1.cc \ stdlib/std/hashing/sha2.cc \ stdlib/std/io/network/http.cc \ stdlib/std/io/network/tcp.cc \ stdlib/std/io/network/smtp.cc \ stdlib/std/io/file.cc \ stdlib/std/io/console.cc \ stdlib/std/io/xml.cc \ stdlib/std/type/reflection.cc \ stdlib/std/type/string.cc \ stdlib/std/type/matrix.cc \ stdlib/std/type/array.cc \ stdlib/std/type/map.cc \ stdlib/std/type/type.cc \ stdlib/std/type/binary.cc \ stdlib/std/encoding.cc \ stdlib/std/os/dll.cc \ stdlib/std/os/time.cc \ stdlib/std/os/threads.cc \ stdlib/std/os/process.cc \ stdlib/std/pcre.cc \ stdlib/std/math.cc STDOBJ=$(STDSRC:.cc=.so) all: stdlib stdlib: $(STDOBJ) .cc.so: mkdir -p `dirname $< | sed -e 's/stdlib/stdlib\/build/'` $(CXX) $< -o `dirname $< | sed -e 's/stdlib/stdlib\/build/'`/`basename $< .cc`.so $(CFLAGS) $(LDFLAGS) I have two questions : 1 - The problem is that the make command, i really don't know why, doesn't check if a file was modified and launch the build process on ALL the files no matter what, so if i need to build only one file, i have to build them all or use the command : make path/to/single/file.so Is there any way to solve this? 2 - Any way to do this in a "cleaner" way without have to distribute all the build directories with sources? Thanks

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• std::thread and class constructor and destructor

  - by toeplitz

  When testing threads in C++11 I have created the following example: #include <iostream> #include <thread> class Foo { public: Foo(void) { std::cout << "Constructor called: " << this << std::endl; } ~Foo(void) { std::cout << "Destructor called: " << this << std::endl; } void operator()() const { std::cout << "Operatior called: " << this << std::endl; } }; void test_normal(void) { std::cout << "====> Standard example:" << std::endl; Foo f; } void test_thread(void) { std::cout << "====> Thread example:" << std::endl; Foo f; std::thread t(f); t.detach(); } int main(int argc, char **argv) { test_normal(); test_thread(); for(;;); } Which prints the following: Why is the destructor called 6 times for the thread? And why does the thread report different memory locations?

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• right usage of std::uncaught_exception in a destructor

  - by Vokuhila-Oliba

  There are some articles concluding "never throw an exception from a destructor", and "std::uncaught_exception() is not useful", for example: http://www.gotw.ca/gotw/047.htm (written by Herb Sutter) But it seems that I am not getting the point. So I wrote a small testing example (see below). Since everything is fine with the testing example I would very appreciate some comments regarding what might be wrong with it. testing results: ./main Foo::~Foo(): caught exception - but have pending exception - ignoring int main(int, char**): caught exception: from int Foo::bar(int) ./main 1 Foo::~Foo(): caught exception - but *no* exception is pending - rethrowing int main(int, char**): caught exception: from Foo::~Foo() // file main.cpp // build with e.g. "make main" // tested successfully on Ubuntu-Karmic with g++ v4.4.1 #include <iostream> class Foo { public: int bar(int i) { if (0 == i) throw(std::string("from ") + __PRETTY_FUNCTION__); else return i+1; } ~Foo() { bool exc_pending=std::uncaught_exception(); try { bar(0); } catch (const std::string &e) { // ensure that no new exception has been created in the meantime if (std::uncaught_exception()) exc_pending = true; if (exc_pending) { std::cerr << __PRETTY_FUNCTION__ << ": caught exception - but have pending exception - ignoring" << std::endl; } else { std::cerr << __PRETTY_FUNCTION__ << ": caught exception - but *no* exception is pending - rethrowing" << std::endl; throw(std::string("from ") + __PRETTY_FUNCTION__); } } } }; int main(int argc, char** argv) { try { Foo f; // will throw an exception in Foo::bar() if no arguments given. Otherwise // an exception from Foo::~Foo() is thrown. f.bar(argc-1); } catch (const std::string &e) { std::cerr << __PRETTY_FUNCTION__ << ": caught exception: " << e << std::endl; } return 0; }

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• conflicting declaration when filling a static std::map class member variable

  - by Max

  I have a class with a static std::map member variable that maps chars to a custom type Terrain. I'm attempting to fill this map in the class's implementation file, but I get several errors. Here's my header file: #ifndef LEVEL_HPP #define LEVEL_HPP #include <bitset> #include <list> #include <map> #include <string> #include <vector> #include "libtcod.hpp" namespace yarl { namespace level { class Terrain { // Member Variables private: std::bitset<5> flags; // Member Functions public: explicit Terrain(const std::string& flg) : flags(flg) {} (...) }; class Level { private: static std::map<char, Terrain> terrainTypes; (...) }; } } #endif and here's my implementation file: #include <bitset> #include <list> #include <map> #include <string> #include <vector> #include "Level.hpp" #include "libtcod.hpp" using namespace std; namespace yarl { namespace level { /* fill Level::terrainTypes */ map<char,Terrain> Level::terrainTypes['.'] = Terrain("00001"); // clear map<char,Terrain> Level::terrainTypes[','] = Terrain("00001"); // clear map<char,Terrain> Level::terrainTypes['\''] = Terrain("00001"); // clear map<char,Terrain> Level::terrainTypes['`'] = Terrain("00001"); // clear map<char,Terrain> Level::terrainTypes[178] = Terrain("11111"); // wall (...) } } I'm using g++, and the errors I get are src/Level.cpp:15: error: conflicting declaration ‘std::map, std::allocator yarl::level::Level::terrainTypes [46]’ src/Level.hpp:104: error: ‘yarl::level::Level::terrainTypes’ has a previous declaration as ‘std::map, std::allocator yarl::level::Level::terrainTypes’ src/Level.cpp:15: error: declaration of ‘std::map, std::allocator yarl::level::Level::terrainTypes’ outside of class is not definition src/Level.cpp:15: error: conversion from ‘yarl::level::Terrain’ to non-scalar type ‘std::map, std::allocator ’ requested src/Level.cpp:15: error: ‘yarl::level::Level::terrainTypes’ cannot be initialized by a non-constant expression when being declared I get a set of these for each map assignment line in the implementation file. Anyone see what I'm doing wrong? Thanks for your help.

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• std::basic_string full specialization (g++ conflict)

  - by SoapBox

  I am trying to define a full specialization of std::basic_string< char, char_traits<char>, allocator<char> > which is typedef'd (in g++) by the <string> header. The problem is, if I include <string> first, g++ sees the typedef as an instantiation of basic_string and gives me errors. If I do my specialization first then I have no issues. I should be able to define my specialization after <string> is included. What do I have to do to be able to do that? My Code: #include <bits/localefwd.h> //#include <string> // <- uncommenting this line causes compilation to fail namespace std { template<> class basic_string< char, char_traits<char>, allocator<char> > { public: int blah() { return 42; } size_t size() { return 0; } const char *c_str() { return ""; } void reserve(int) {} void clear() {} }; } #include <string> #include <iostream> int main() { std::cout << std::string().blah() << std::endl; } The above code works fine. But, if I uncomment the first #include <string> line, I get the following compiler errors: blah.cpp:7: error: specialization of ‘std::basic_string<char, std::char_traits<char>, std::allocator<char> >’ after instantiation blah.cpp:7: error: redefinition of ‘class std::basic_string<char, std::char_traits<char>, std::allocator<char> >’ /usr/include/c++/4.4/bits/stringfwd.h:52: error: previous definition of ‘class std::basic_string<char, std::char_traits<char>, std::allocator<char> >’ blah.cpp: In function ‘int main()’: blah.cpp:22: error: ‘class std::string’ has no member named ‘blah’ Line 52 of /usr/include/c++/4.4/bits/stringfwd.h: template<typename _CharT, typename _Traits = char_traits<_CharT>, typename _Alloc = allocator<_CharT> > class basic_string; As far as I know this is just a forward delcaration of the template, NOT an instantiation as g++ claims. Line 56 of /usr/include/c++/4.4/bits/stringfwd.h: typedef basic_string<char> string; As far as I know this is just a typedef, NOT an instantiation either. So why are these lines conflicting with my code? What can I do to fix this other than ensuring that my code is always included before <string>?

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• tr1::shared_ptr, Eclipse, and autocomplete woes

  - by seabass

  Does anyone know if there is a plugin or some sort of fix to be able to autocomplete on variables of type tr1::shared_ptr?

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• Vector of vectors of T in template<T> class

  - by topright

  Why this code does not compile (Cygwin)? #include <vector> template <class Ttile> class Tilemap { typedef std::vector< Ttile > TtileRow; typedef std::vector< TtileRow > TtileMap; typedef TtileMap::iterator TtileMapIterator; // error here }; error: type std::vector<std::vector<Ttile, std::allocator<_CharT> >, std::allocator<std::vector<Ttile, std::allocator<_CharT> > > >' is not derived from typeTilemap'

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• Error while linking libvorbisfile.dylib into Mac application

  - by computergeek6

  I'm working on a program that loads sounds from Ogg Vorbis files, but whatever I do, the XCode project just doesn't seem to want to link libvorbisfile.a into my program. I keep getting linking errors: "_ov_read", referenced from: GSound::GSound(GWorld*, std::basic_string<char, std::char_traits<char>, std::allocator<char> >)in GSound.o GSound::GSound(GWorld*, std::basic_string<char, std::char_traits<char>, std::allocator<char> >)in GSound.o "_ov_clear", referenced from: GSound::GSound(GWorld*, std::basic_string<char, std::char_traits<char>, std::allocator<char> >)in GSound.o GSound::GSound(GWorld*, std::basic_string<char, std::char_traits<char>, std::allocator<char> >)in GSound.o "_ov_info", referenced from: GSound::GSound(GWorld*, std::basic_string<char, std::char_traits<char>, std::allocator<char> >)in GSound.o GSound::GSound(GWorld*, std::basic_string<char, std::char_traits<char>, std::allocator<char> >)in GSound.o "_ov_open", referenced from: GSound::GSound(GWorld*, std::basic_string<char, std::char_traits<char>, std::allocator<char> >)in GSound.o GSound::GSound(GWorld*, std::basic_string<char, std::char_traits<char>, std::allocator<char> >)in GSound.o ld: symbol(s) not found

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• How to bind std::map to Lua with LuaBind

  - by MahanGM

  Is this possible in lua to achieve? player.scripts["movement"].properties["stat"] = "stand" print (player.scripts["movement"].properties["stat"]) I've done getter method in c++ with this approach: luabind::object FakeScript::getProp() { luabind::object obj = luabind::newtable(L); for(auto i = this->properties.begin(); i != this->properties.end(); i++) { obj[i->first] = i->second; } return obj; } But I'm stuck with setter. The first line in lua code which I'm trying to set value "stand" for key "stat" is not going to work and it keep redirecting me to the getter method. Setter method only works when I drop ["stat"] from properties. I can do something like this for setter in my script: player.scripts["movement"].properties = {stat = "stand"} But this isn't what I want because I have to go through my real keys in c++ to determine which key is placed in setter argument table value. This is my map in class: std::map<std::string, std::string> properties;

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• How to std::find using a Compare object?

  - by dehmann

  I am confused about the interface of std::find. Why doesn't it take a Compare object that tells it how to compare two objects? If I could pass a Compare object I could make the following code work, where I would like to compare by value, instead of just comparing the pointer values directly: typedef std::vector<std::string*> Vec; Vec vec; std::string* s1 = new std::string("foo"); std::string* s2 = new std::string("foo"); vec.push_back(s1); Vec::const_iterator found = std::find(vec.begin(), vec.end(), s2); // not found, obviously, because I can't tell it to compare by value delete s1; delete s2; Is the following the recommended way to do it? template<class T> struct MyEqualsByVal { const T& x_; MyEqualsByVal(const T& x) : x_(x) {} bool operator()(const T& y) const { return *x_ == *y; } }; // ... vec.push_back(s1); Vec::const_iterator found = std::find_if(vec.begin(), vec.end(), MyEqualsByVal<std::string*>(s2)); // OK, will find "foo"

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• Exporting classes containing std:: objects (vector, map, etc) from a dll

  - by RnR

  I'm trying to export classes from a DLL that contain objects such as std::vectors and std::stings - the whole class is declared as dll export through: class DLL_EXPORT FontManager { The problem is that for members of the complex types I get this warning: warning C4251: 'FontManager::m__fonts' : class 'std::map<_Kty,_Ty' needs to have dll-interface to be used by clients of class 'FontManager' with [ _Kty=std::string, _Ty=tFontInfoRef ] I'm able to remove some of the warnings by putting the following forward class declaration before them even though I'm not changing the type of the member variables themselves: template class DLL_EXPORT std::allocator<tCharGlyphProviderRef>; template class DLL_EXPORT std::vector<tCharGlyphProviderRef,std::allocator<tCharGlyphProviderRef> >; std::vector<tCharGlyphProviderRef> m_glyphProviders; Looks like the forward declaration "injects" the DLL_EXPORT for when the member is compiled but is it safe? Does it realy change anything when the client compiles this header and uses the std container on his side? Will it make all future uses of such a container DLL_EXPORT (and possibly not inline?)? And does it really solve the problem that the warning tries to warn about? Is this warning anything I should be worried about or would it be best to disable it in the scope of these constructs? The clients and the dll will always be built using the same set of libraries and compilers and those are header only classes... I'm using Visual Studio 2003 with the standard STD library. ---- Update ---- I'd like to target you more though as I see the answers are general and here we're talking about std containers and types (such as std::string) - maybe the question really is: Can we disable the warning for standard containers and types available to both the client and the dll through the same library headers and treat them just as we'd treat an int or any other built-in type? (It does seem to work correctly on my side.) If so would should be the conditions under which we can do this? Or should maybe using such containers be prohibited or at least ultra care taken to make sure no assignment operators, copy constructors etc will get inlined into the dll client? In general I'd like to know if you feel designing a dll interface having such objects (and for example using them to return stuff to the client as return value types) is a good idea or not and why - I'd like to have a "high level" interface to this functionality... maybe the best solution is what Neil Butterworth suggested - creating a static library?

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