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  • Problem using graphics.h in Ubuntu

    - by blooooomer
    # include<stdio.h> # include<graphics.h> # include<math.h> using namespace std; int main(void) { int gd=DETECT,gm; int r,x,y,p,xc=320,yc=240; initgraph(&gd,&gm,NULL); cleardevice(); printf("Enter the radius "); scanf("%d",&r); x=0; y=r; putpixel(xc+x,yc-y,1); p=3-(2*r); for(x=0;x<=y;x++) { if (p<0) { y=y; p=(p+(4*x)+6); } else { y=y-1; p=p+((4*(x-y)+10)); } putpixel(xc+x,yc-y,1); putpixel(xc-x,yc-y,2); putpixel(xc+x,yc+y,3); putpixel(xc-x,yc+y,4); putpixel(xc+y,yc-x,5); putpixel(xc-y,yc-x,6); putpixel(xc+y,yc+x,7); putpixel(xc-y,yc+x,8); } getch(); closegraph(); } installed graphics.h compiled using gcc filename.cpp -0 filename -lgraph then used ./filename the window apperared for 10 seconds and the error below appears: [xcb] Unknown sequence number while processing queue [xcb] Most likely this is a multi-threaded client and XInitThreads has not been called [xcb] Aborting, sorry about that. heart: ../../src/xcb_io.c:273: poll_for_event: Assertion `!xcb_xlib_threads_sequence_lost' failed. Aborted Any solutions?

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  • C++ Iterator lifetime and detecting invalidation

    - by DK.
    Based on what's considered idiomatic in C++11: should an iterator into a custom container survive the container itself being destroyed? should it be possible to detect when an iterator becomes invalidated? are the above conditional on "debug builds" in practice? Details: I've recently been brushing up on my C++ and learning my way around C++11. As part of that, I've been writing an idiomatic wrapper around the uriparser library. Part of this is wrapping the linked list representation of parsed path components. I'm looking for advice on what's idiomatic for containers. One thing that worries me, coming most recently from garbage-collected languages, is ensuring that random objects don't just go disappearing on users if they make a mistake regarding lifetimes. To account for this, both the PathList container and its iterators keep a shared_ptr to the actual internal state object. This ensures that as long as anything pointing into that data exists, so does the data. However, looking at the STL (and lots of searching), it doesn't look like C++ containers guarantee this. I have this horrible suspicion that the expectation is to just let containers be destroyed, invalidating any iterators along with it. std::vector certainly seems to let iterators get invalidated and still (incorrectly) function. What I want to know is: what is expected from "good"/idiomatic C++11 code? Given the shiny new smart pointers, it seems kind of strange that STL allows you to easily blow your legs off by accidentally leaking an iterator. Is using shared_ptr to the backing data an unnecessary inefficiency, a good idea for debugging or something expected that STL just doesn't do? (I'm hoping that grounding this to "idiomatic C++11" avoids charges of subjectivity...)

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  • Checking preconditions or not

    - by Robert Dailey
    I've been wanting to find a solid answer to the question of whether or not to have runtime checks to validate input for the purposes of ensuring a client has stuck to their end of the agreement in design by contract. For example, consider a simple class constructor: class Foo { public: Foo( BarHandle bar ) { FooHandle handle = GetFooHandle( bar ); if( handle == NULL ) { throw std::exception( "invalid FooHandle" ); } } }; I would argue in this case that a user should not attempt to construct a Foo without a valid BarHandle. It doesn't seem right to verify that bar is valid inside of Foo's constructor. If I simply document that Foo's constructor requires a valid BarHandle, isn't that enough? Is this a proper way to enforce my precondition in design by contract? So far, everything I've read has mixed opinions on this. It seems like 50% of people would say to verify that bar is valid, the other 50% would say that I shouldn't do it, for example consider a case where the user verifies their BarHandle is correct, but a second (and unnecessary) check is also being done inside of Foo's constructor.

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  • Recording slow web stream

    - by Budric
    I'm trying to record an mpeg2 video stream from a website that doesn't have the greatest bandwidth. The video often buffers. I want to download the stream and watch it offline. The extract stream format received is: Stream #0.0[0x44]: Audio: mp2, 48000 Hz, stereo, s16, 192 kb/s Stream #0.1[0x45]: Video: mpeg2video (Main), yuv420p, 704x576 [PAR 16:11 DAR 16:9], 15000 kb/s, 27.19 fps, 25 tbr, 90k tbn, 50 tbc I use the following tool to transocde the stream: ffmpeg -i "http://url" -y -vcodec libx264 -b 3000k -acodec copy /tmp/stream.mp4 Unfortunately after a few seconds ffmpeg stops recording with an error [mpegts @ 0x1f0b9c0] PES packet size mismatch [mp2 @ 0x1f14640] incomplete frame Error while decoding stream #0.0 [mpeg2video @ 0x1f16860] ac-tex damaged at 0 26 [mpeg2video @ 0x1f16860] Warning MVs not available I've tried encoding with vlc as well with similar issues. Although vlc doesn't stop encoding, the output video has regions where it hangs. vlc -I dummy "http://url" --network-caching="1000" --sout="#transcode{vcodec=h264,vb=3000,acodec=mp3,ab=192}:std{access=file,mux=mp4,dst=/tmp/stream.mp4}" [mpeg2video @ 0x7f2d4c001e20] ac-tex damaged at 9 33 [mpeg2video @ 0x7f2d4c001e20] Warning MVs not available [mpeg2video @ 0x7f2d4c001e20] concealing 132 DC, 132 AC, 132 MV errors [mpeg2video @ 0x7f2d4c001e20] ac-tex damaged at 16 17 [mpeg2video @ 0x7f2d4c001e20] Warning MVs not available [mpeg2video @ 0x7f2d4c001e20] concealing 836 DC, 836 AC, 836 MV errors libdvbpsi error (PSI decoder): TS discontinuity (received 4, expected 3) for PID 0 I also tried flv transcoding and it shows up with its own set of issues, like output flv file hangs in certain parts. Anyone know what's wrong or how to fix this?

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  • How to install custom c library?

    - by arijit
    I just wanted to add a c library to Ubuntu which was created by Harvard University for cs50 course. They provided instructions for how to install the library which is listed below. Debian, Ubuntu First become root, as with: sudo su - Then install the CS50 Library as follows: apt-get install gcc wget http://mirror.cs50.net/library/c/cs50-library-c-3.1.zip unzip cs50-library-c-3.1.zip rm -f cs50-library-c-3.1.zip cd cs50-library-c-3.1 gcc -c -ggdb -std=c99 cs50.c -o cs50.o ar rcs libcs50.a cs50.o chmod 0644 cs50.h libcs50.a mkdir -p /usr/local/include chmod 0755 /usr/local/include mv -f cs50.h /usr/local/include mkdir -p /usr/local/lib chmod 0755 /usr/local/lib mv -f libcs50.a /usr/local/lib cd .. rm -rf cs50-library-c-3.1 I did exactly as directed. But the compiler reported “Undefined reference to a function”--the function was Get String. So, I searched for a solution and found one. It said to use the -l switch. Now when I compile I use something like: gcc –o hello.c hello –lcs50 (I don’t remember the exact command.) However, I cannot use the make command, which is easier to use. I understand that there is some problem with linking the library. What is a good solution to this problem?

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  • Trying to compile from source newest apache with newest openssl

    - by AlexMA
    I need to install apache 2.4.10 using openssl 1.0.1i. I compiled openssl from source with: $ ./config \ --prefix=/opt/openssl-1.0.1i \ --openssldir=/opt/openssl-1.0.1i $ make $ sudo make install and Apache with: ./configure --prefix=/etc/apache2 \ --enable-access_compat=shared \ --enable-actions=shared \ --enable-alias=shared \ --enable-allowmethods=shared \ --enable-auth_basic=shared \ --enable-authn_core=shared \ --enable-authn_file=shared \ --enable-authz_core=shared \ --enable-authz_groupfile=shared \ --enable-authz_host=shared \ --enable-authz_user=shared \ --enable-autoindex=shared \ --enable-dir=shared \ --enable-env=shared \ --enable-headers=shared \ --enable-include=shared \ --enable-log_config=shared \ --enable-mime=shared \ --enable-negotiation=shared \ --enable-proxy=shared \ --enable-proxy_http=shared \ --enable-rewrite=shared \ --enable-setenvif=shared \ --enable-ssl=shared \ --enable-unixd=shared \ --enable-ssl \ --with-ssl=/opt/openssl-1.0.1i \ --enable-ssl-staticlib-deps \ --enable-mods-static=ssl make (would run sudo make install next but I get an error) I'm essentially following the guide here except with newer slightly newer versions. My problem is I get a linker error when I run make for apache: Making all in support make[1]: Entering directory `/home/developer/downloads/httpd-2.4.10/support' make[2]: Entering directory `/home/developer/downloads/httpd-2.4.10/support' /usr/share/apr-1.0/build/libtool --silent --mode=link x86_64-linux-gnu-gcc -std=gnu99 -pthread -L/opt/openssl-1.0.1i/lib -lssl -lcrypto \ -o ab ab.lo /usr/lib/x86_64-linux-gnu/libaprutil-1.la /usr/lib/x86_64-linux-gnu/libapr-1.la -lm /usr/bin/ld: /opt/openssl-1.0.1i/lib/libcrypto.a(dso_dlfcn.o): undefined reference to symbol 'dlclose@@GLIBC_2.2.5' I tried the answer here, but no luck. I would prefer to just use aptitude, but unfortunately the versions I need aren't available yet. If anyone knows how to fix the linker problem (or what I think is a linker problem), or knows of a better way to tell apache to use a newer openssl, it would be greatly appreciated; I've got apache 1.0.1i working otherwise.

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  • Reconstruct a file from a TCP stream

    - by Abhishek Chanda
    I have a client and a server and a third box which sees all packets from the server to the client (but not the other way around). Now when the client requests a file from the server (over HTTP), the third box sees the response. I am trying to reconstruct the file there. I am using libpcap to capture TCP datagrams and trying to reconstruct the file there. Here is what I did Listen for packets on an interface Group all packets which have the same ACK number Sort the group based on SEQ number Extract data from each packet and combine them and write to the disk The problem is, the file thus generated is not exactly the same as the original file. Does everything sound correct here? Some more details: I am using C++ The packet data is being stored as std::vector<char> I did change the byte order while reading the ack number and seq number from the packet using ntohl I am not sure if I need to change the byte order for the data as well. I tried to reverse the data from each packet before combining them, even that did not work. Is there something I am missing?

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  • Subdomain redirect to WWW

    - by manix
    I have the domain example.com and the test.example.com running on apache server. For some reason when I try to visit test.example it is redirected to www.test.example and by consequence a Server not found error is displayed in the browser. Both .htaccess (root and subdomain folder) files are empty. Additional facts I have another subdomain xyz.example.com pointed to public_html/xyz directory with some content inside (index.html with "hello world message") and it works fine if I use xyz.example.com instead of www.xyz.example.com. So, can you help me to point to the right direction in order. I have a vps and I am able to change any file if is required. Below you can find my virtual host configuration. <VirtualHost xx.xxx.xxx:80> ServerName test.example.com ServerAlias www.test.example.com DocumentRoot /home/example/public_html/test ServerAdmin [email protected] UseCanonicalName Off CustomLog /usr/local/apache/domlogs/test.example.com combined CustomLog /usr/local/apache/domlogs/test.example.com-bytes_log "%{%s}t %I .\n%{%s}t %O ." ScriptAlias /cgi-bin/ /home/example/public_html/test/cgi-bin/ # To customize this VirtualHost use an include file at the following location # Include "/usr/local/apache/conf/userdata/std/2/example/test.example.com/*.conf" </VirtualHost>

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  • Internet Explorer menu z-order problem [migrated]

    - by robgt
    I have what appears to be a z-order problem with Internet Explorer 9. It might be in other IE versions also, but not tested. I have to assume so. This page: http://www.modelhelicopters.co.uk/partsfinder/trex500esp/frames If you hover over the "All pages for this model" menu item on the parts finder menu bar (below the currency selector) - it should drop down a list of all the parts finder pages for the selected model helicopter. If you view the same page in IE or Chrome etc, you will see how it should appear. In IE9, the menu gets cut off at the top of the main exploded view image - suggesting the z-order is wrong. I have tried amending this with a jquery snippet but it didn't fix IE9. I know the code was inserted by jquery as shown by firebug in firefox. $j('div.std img[src*="/partsfinder/img"]').attr("style","position:relative;z-index:-100;"); I really do not know why this is not working.

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  • M-Audio Delta starts up at wrong sample rate

    - by steevc
    When the PC starts my M-Audio Delta 66 is using 48000kHz sampling rate when it is set for 44100 in Envy24. This causes audio to play slower than it should. This is in Kubuntu 14.04 on my new PC using an AMD A8 6500 with 8GB. When I first installed it seemed okay, but at some point it went wrong and has been doing this consistently since then. Kernel is 3.13.0-24-generic #47-Ubuntu SMP Fri May 2 23:31:42 UTC 2014 i686 athlon i686 GNU/Linux steve@slarti:~$ cat /proc/asound/card2/pcm0p/sub0/hw_params access: MMAP_INTERLEAVED format: S32_LE subformat: STD channels: 10 rate: 48000 (48000/1) period_size: 441 buffer_size: 3528 I can get it to switch to 44100 if I disable/enable the Delta in Pulseaudio volume control, but I have to do this every day and the sound still seems distorted. I can't see any issues in any of the config or log files I can find. If I boot the PC with a Mint Live USB it starts at 44100 and sound fine. Originally reported on Youtube is playing at the wrong speed - maybe soundcard related, but I'll close that and have this more relevant question instead.

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  • Draw contour around object in Opengl

    - by Maciekp
    I need to draw contour around 2d objects in 3d space. I tried drawing lines around object(+points to fill the gap), but due to line width, some part of it(~50%) was covering object. I tried to use stencil buffer, to eliminate this problem, but I got sth like this(contour is green): http://goo.gl/OI5uc (sorry I can't post images, due to my reputation) You can see(where arrow points), that some parts of line are behind object, and some are above. This changes when I move camera, but always there is some part, that is covering it. Here is code, that I use for drawing object: glColorMask(1,1,1,1); std::list<CObjectOnScene*>::iterator objIter=ptr->objects.begin(),objEnd=ptr->objects.end(); int countStencilBit=1; while(objIter!=objEnd) { glColorMask(1,1,1,1); glStencilFunc(GL_ALWAYS,countStencilBit,countStencilBit); glStencilOp(GL_REPLACE,GL_KEEP,GL_REPLACE ); (*objIter)->DrawYourVertices(); glStencilFunc(GL_NOTEQUAL,countStencilBit,countStencilBit); glStencilOp(GL_KEEP,GL_KEEP,GL_REPLACE); (*objIter)->DrawYourBorder(); ++objIter; ++countStencilBit; } I've tried different settings of stencil buffer, but always I was getting sth like that. Here is question: 1.Am I setting stencil buffer wrong? 2. Are there any other simple ways to create contour on such objects? Thanks in advance.

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  • C++: calling non-member functions with the same syntax of member ones

    - by peoro
    One thing I'd like to do in C++ is to call non-member functions with the same syntax you call member functions: class A { }; void f( A & this ) { /* ... */ } // ... A a; a.f(); // this is the same as f(a); Of course this could only work as long as f is not virtual (since it cannot appear in A's virtual table. f doesn't need to access A's non-public members. f doesn't conflict with a function declared in A (A::f). I'd like such a syntax because in my opinion it would be quite comfortable and would push good habits: calling str.strip() on a std::string (where strip is a function defined by the user) would sound a lot better than calling strip( str );. most of the times (always?) classes provide some member functions which don't require to be member (ie: are not virtual and don't use non-public members). This breaks encapsulation, but is the most practical thing to do (due to point 1). My question here is: what do you think of such feature? Do you think it would be something nice, or something that would introduce more issues than the ones it aims to solve? Could it make sense to propose such a feature to the next standard (the one after C++0x)? Of course this is just a brief description of this idea; it is not complete; we'd probably need to explicitly mark a function with a special keyword to let it work like this and many other stuff.

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  • C++ and SDL Trouble Creating a STL Vector of a Game Object

    - by Jackson Blades
    I am trying to create a Space Invaders clone using C++ and SDL. The problem I am having is in trying to create Waves of Enemies. I am trying to model this by making my Waves a vector of 8 Enemy objects. My Enemy constructor takes two arguments, an x and y offset. My Wave constructor also takes two arguments, an x and y offset. What I am trying to do is have my Wave constructor initialize a vector of Enemies, and have each enemy given a different x offset so that they are spaced out appropriately. Enemy::Enemy(int x, int y) { box.x = x; box.y = y; box.w = ENEMY_WIDTH; box.h = ENEMY_HEIGHT; xVel = ENEMY_WIDTH / 2; } Wave::Wave(int x, int y) { box.x = x; box.y = y; box.w = WAVE_WIDTH; box.y = WAVE_HEIGHT; xVel = (-1)*ENEMY_WIDTH; yVel = 0; std::vector<Enemy> enemyWave; for (int i = 0; i < enemyWave.size(); i++) { Enemy temp(box.x + ((ENEMY_WIDTH + 16) * i), box.y); enemyWave.push_back(temp); } } I guess what I am asking is if there is a cleaner, more elegant way to do this sort of initialization with vectors, or if this is right at all. Any help is greatly appreciated.

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  • PhysX Capsule Character Controller floating above ground

    - by Jannie
    I am using PhysX Version 3.0.2 in the simulation package I'm working on, and I've encountered some bizarre behavior with the capsule character controller. When I set the controller's height and radius to the appropriate values (r = 0.25, h = 1.86)it behaves correctly (moving along the ground, colliding with other objects, and so on) except that the capsule itself is floating above the ground. The actor will then bump his head when trying to get through a door, since the capsule is the correct height but also floating above the ground. This image should illustrate what I'm going on about: One can clearly see that the rest of the scene has their collision bodies wrapped correctly, it's just the capsule that's going wrong! The stop-gap I've implemented is creating a smaller capsule and giving it an offset, but I need to implement ray-picking for the controller next so the capsule has to surround the character model properly. Here's my character creation code (with height = 1.86f and radius = 0.25f): NxController* D3DPhysXManager::CreateCharacterController( std::string l_stdsControllerName, float l_fHeight, float l_fRadius, D3DXVECTOR3 l_v3Position ) { NxCapsuleControllerDesc l_CapsuleControllerDescription; l_CapsuleControllerDescription.height = l_fHeight; l_CapsuleControllerDescription.radius = l_fRadius; l_CapsuleControllerDescription.position.set( l_v3Position.x, l_v3Position.y, l_v3Position.z ); l_CapsuleControllerDescription.callback = &this->m_ControllerHitReport; NxController* l_pController = this->m_pControllerManager->createController( this->m_pScene, l_CapsuleControllerDescription ); this->m_pControllerMap.insert( l_ControllerValuePair( l_stdsControllerName, l_pController ) ); return l_pController; } Any help at all would be appreciated, I just can't figure this one out! P.S. I've found a couple of (rather old) threads describing the same issue, but it seems they couldn't find a solution either. Here are the links: http://forum-archive.developer.nvidia.com/index.php?showtopic=6409 http://forum-archive.developer.nvidia.com/index.php?showtopic=3272 http://www.ogre3d.org/addonforums/viewtopic.php?f=8&t=23003

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  • Draw contour around object in Opengl

    - by Maciekp
    I need to draw contour around 2d objects in 3d space. I tried drawing lines around object(+points to fill the gap), but due to line width, some part of it(~50%) was covering object. I tried to use stencil buffer, to eliminate this problem, but I got sth like this(contour is green): http://goo.gl/OI5uc (sorry I can't post images, due to my reputation) You can see(where arrow points), that some parts of line are behind object, and some are above. This changes when I move camera, but always there is some part, that is covering it. Here is code, that I use for drawing object: glColorMask(1,1,1,1); std::list<CObjectOnScene*>::iterator objIter=ptr->objects.begin(),objEnd=ptr->objects.end(); int countStencilBit=1; while(objIter!=objEnd) { glColorMask(1,1,1,1); glStencilFunc(GL_ALWAYS,countStencilBit,countStencilBit); glStencilOp(GL_REPLACE,GL_KEEP,GL_REPLACE ); (*objIter)->DrawYourVertices(); glStencilFunc(GL_NOTEQUAL,countStencilBit,countStencilBit); glStencilOp(GL_KEEP,GL_KEEP,GL_REPLACE); (*objIter)->DrawYourBorder(); ++objIter; ++countStencilBit; } I've tried different settings of stencil buffer, but always I was getting sth like that. Here is question: 1.Am I setting stencil buffer wrong? 2. Are there any other simple ways to create contour on such objects? Thanks in advance. EDIT: 1. I don't have normals of objects. 2. Object can be concave. 3. I can't use shaders(see below why).

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  • If you favor "T *var", do you ever write "T*"?

    - by Roger Pate
    Thinking about where we place our asterisks; how do those that prefer to keep the "pointerness" away from the type and with the identifier (int *i) write code when the identifier is missing? void f(int*); // 1 void f(int *); // 2 The former seems much more common, no matter what your preference when with the identifier. Is this a special case? What makes it an exception? However, the first still isn't universal, because I have seen the latter style. Besides consistency along the lines of "there's always a space with the identifier, so we have one without", are there any other reasons to prefer it? What about casts or array and function types? How would you re-write these: (void*)var /*or*/ (void *)var int[3] /*or*/ int [3] // more relevant in C++ than C: Example<int[3]> void(int) /*or*/ void (int) // more relevant in C++ than C: std::function<void(int)> The latter two would rarely, if ever, be used in C, but are seen with C++ templates.

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  • C++ function templates, function name confusion. This is funny [migrated]

    - by nashmaniac
    Alright so heres the program and works absolutely right #include <iostream> using namespace std; template <typename T> void Swap(T &a , T &b); int main(){ int i = 10; int j = 20; cout<<"i, j = " << i <<" , " <<j<<endl; Swap(i,j); cout<<"i, j = " << i <<" , " <<j<<endl; } template <typename T> void Swap(T &a , T &b){ T temp; temp = a ; a = b; b= temp; } but when I change the function's name from Swap to swap it generates an error saying error: call of overloaded 'swap(int&, int&)' is ambiguous| note: candidates are: void swap(T&, T&) [with T = int]| ||=== Build finished: 1 errors, 0 warnings ===| what happened is it a rule to start functions using templates to start with a capital letter ?

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  • 7 drived classes with one common base class

    - by user144905
    i have written the following code, //main.cpp #include<iostream> #include<string> #include"human.h" #include"computer.h" #include"referee.h" #include"RandomComputer.h" #include"Avalanche.h" #include"Bureaucrat.h" #include"Toolbox.h" #include"Crescendo.h" #include"PaperDoll.h" #include"FistfullODollors.h" using namespace std; int main() { Avalanche pla1; Avalanche pla2; referee f; pla1.disp(); for (int i=0;i<5;i++) { cout<<pla2.mov[i]; } return 0; } in this program all included classes except referee.h and human.h are drived from computer.h. each drived calls has a char array variable which is initialized when a member of a drived class is declared. the problem is that when i declare tow diffrent drived class memebers lets say Avalache and ToolBox. upon printing the char array for one of them using for loop it prints nothing. However if i declare only one of them in main.cpp the it works properly. and the file for computer.h is as such: #ifndef COMPUTER_H #define COMPUTER_H class computer { public: int nump; char mov[]; void disp(); }; #endif ToolBox.h is like this: #ifndef TOOLBOX_H #define TOOLBOX_H #include"computer.h" class Toolbox: public computer { public: Toolbox(); }; #endif finally Avalanche.h is as following: #ifndef AVALANCHE_H #define AVALANCHE_H #include"computer.h" class Avalanche: public computer { public: Avalanche(); }; #endif

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  • Writing a program in C++ and I need help [migrated]

    - by compscinoob
    So I am a new to this. I am trying to write a program with a function double_product(vector< double a, vector< double b) that computes the scalar product of two vectors. The scalar product is $a_{0}b_{0}+a_{1}b_{1}+...a_{n-1}b_{n-1}$. Here is what I have. It is a mess, but I am trying! #include<iostream> #include<vector> using namespace std; class Scalar_product { public: Scalar_product(vector<double> a, vector<bouble> b); }; double scalar_product(vector<double> a, vector<double> b) { double product = 0; for (int i=0; i <=a.size()-1; i++) for (int i=0; i <=b.size()-1; i++) product = product + (a[i])*(b[i]); return product; } int main() { cout << product << endl; return 0; }

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  • "bug" in C++11 text by Stroustrup?

    - by Astara
    I found an apparent contradiction in the c++ text having to do with the result of the c_str() function operating on std:strings (in my copy, the definition and contradiction are on p1040). First it defines the c_str() function as something that produces a 'C-style' (zero-terminated) string, but later it talks about how a C++ c_str value can have embed a 'C'-style, end-of-string terminators (i.e. NUL's) embedded in the string (that is defined by being NUL terminated). Um... does anyone else feel that this is a 'stretching' of the definition of a C-string beyond it's definition? I.e. I think what it means, is that if you were to look at the length() function as applied to the string, it will show a different end of string than using the C-definition of a z-string -- one that can contain any character except NUL, and is terminated by NUL. I likely don't have to worry about it in my of my programs, but it seems like a subtle distinction that makes a C++ c_str, not really a 'C'-string. Am I misunderstanding this issue? Thanks!

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  • What is the best way to store a table in C++

    - by Topo
    I'm programming a decision tree in C++ using a slightly modified version of the C4.5 algorithm. Each node represents an attribute or a column of your data set and it has a children per possible value of the attribute. My problem is how to store the training data set having in mind that I have to use a subset for each node so I need a quick way to only select a subset of rows and columns. The main goal is to do it in the most memory and time efficient possible (in that order of priority). The best way I have thought of is to have an array of arrays (or std::vector), or something like that, and for each node have a list (array, vector, etc) or something with the column,line(probably a tuple) pairs that are valid for that node. I now there should be a better way to do this, any suggestions? UPDATE: What I need is something like this: In the beginning I have this data: Paris 4 5.0 True New York 7 1.3 True Tokio 2 9.1 False Paris 9 6.8 True Tokio 0 8.4 False But for the second node I just need this data: Paris 4 5.0 New York 7 1.3 Paris 9 6.8 And for the third node: Tokio 2 9.1 Tokio 0 8.4 But with a table of millions of records with up to hundreds of columns. What I have in mind is keep all the data in a matrix, and then for each node keep the info of the current columns and rows. Something like this: Paris 4 5.0 True New York 7 1.3 True Tokio 2 9.1 False Paris 9 6.8 True Tokio 0 8.4 False Node 2: columns = [0,1,2] rows = [0,1,3] Node 3: columns = [0,1,2] rows = [2,4] This way on the worst case scenario I just have to waste size_of(int) * (number_of_columns + number_of_rows) * node That is a lot less than having an independent data matrix for each node.

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  • Do Loops kind of Reset every time you go through it?... [closed]

    - by JacKeown
    #include <iostream> using namespace std; int main (void) { cout << " 1\t2\t3\t4\t5\t6\t7\t8\t9" << endl << "" << endl; for (int c = 1; c < 10; c++) { cout << c << "| "; for (int i = 1; i < 10; i++) { cout << i * c << '\t'; } cout << endl; } return 0; } Hey so this code produces a times table...I found it on Google Code's C++ class online...I'm confused about why "i" in the second for loop resets to 1 every time you go through that loop...or is it being declared again in the first parameter? Thanks in advance!

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  • EXC_BAD_ACCESS error when box2d joint is destroyed

    - by colilo
    When I destroy the weldJoint in the update method (see below) I get an EXC_BAD_ACCESS error pointing to the line world->DestroyJoint(weldJoint); in the update method below: -(void) update: (ccTime) dt { int32 velocityIterations = 8; int32 positionIterations = 1; // Instruct the world to perform a single step of simulation. It is // generally best to keep the time step and iterations fixed. world->Step(dt, velocityIterations, positionIterations); // using the iterator pos over the set std::set<BodyPair *>::iterator pos; for(pos = bodiesForJoints.begin(); pos != bodiesForJoints.end(); ++pos) { b2WeldJointDef weldJointDef; BodyPair *bodyPair = *pos; b2Body *bodyA = bodyPair->bodyA; b2Body *bodyB = bodyPair->bodyB; weldJointDef.Initialize(bodyA, bodyB, bodyA->GetWorldCenter()); weldJointDef.collideConnected = false; weldJoint = (b2WeldJoint*) world->CreateJoint(&weldJointDef); // Free the structure we allocated earlier. free(bodyPair); // Remove the entry from the set. bodiesForJoints.erase(pos); } for(b2Body *b = world->GetBodyList(); b; b=b->GetNext()) { if (b->GetUserData() != NULL) { CCSprite *mainSprite = (CCSprite*)b->GetUserData(); if (mainSprite.tag == 1) { mainSprite.position = CGPointMake( b->GetPosition().x * PTM_RATIO, b->GetPosition().y * PTM_RATIO); CGPoint mainSpritePosition = mainSprite.position; if (mainSprite.isMoved) { world->DestroyJoint(weldJoint); } } } } } In the HelloWorldLayer.h I set the weldJoint with the assign property. Am I destroying the joint in the wrong way? I would really appreciate any help. Thanks

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  • I’m new to C++ and unsure about how to improve this code [migrated]

    - by Laian Alsabbagh
    The purpose of the following code is to get a random number of 100 nodes and to distribute these nodes randomly in range 500*500 …(X,Y).. this was the first step #include<iostream> #include <fstream> #include<cmath> using namespace std; int main() { const int x = 0, y = 1; int nodes[100][2]; ofstream myfile; myfile.open ("example.txt"); myfile << "Writing this to a file.\n"; for (int i=0; i<100 ;i++) { nodes[i][x] = rand() % 501; nodes[i][y] = rand() % 501; myfile <<nodes[i][x]<<" "<<nodes[i][y]; } myfile.close(); } now the next step is to improve this code to distribute these nodes in order ( "Imust divide both xy_coordinates as : x= 0-100-200-300-400-500 & y=0-100-200-300-400-500) next is to distribute the nodes (regardless number of nodes) in order range Starting from (0,100 )….(100,100)..(100,200)…….untile i reach the last point (500,500),, ") I’m really confused of how to do it correctly I start to think to define 2 dimensional array , and then to define 2 for loops enter code here Int no_nodes=100; Int XY_coordinate [500][500]; For (int i=0;i<no_nodes; i++) { For (int j=0;j<no_nodes; j++)

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  • Associate a texture to an object (from a data-model, not graphical point of view).

    - by Raveline
    I'm writing a roguelike where objects and floor can be made of different materials. For instance, let's say we can have a wooden chair, an iron chair, a golden chair, and so on. I've got an Object class (I know, the name is terrible), which is more or less using a composite pattern, and a Material class. Material have different important properties (noise, color...). For the time being, there are 5 different instances of materials, created at the initialization of the game. How would connect an instance of Object with one of the 5 instances of materials ? I see three simple solutions : Using a pointer. Simple and brutal. Using an integer material-id, then get the materials out of a table when engine manipulates the object for various purposes (display, attack analysis, etc.). Not very beautiful, I think, and not very flexible. Using an integer material-id, then get the materials out of a std::map. A bit more flexible, but still not perfect. Do you see other possibilities ? If not, what would you choose (and why) ? Thanks in advance !

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