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• Ruby: how does constant-lookup work in instance_eval/class_eval?

  - by Alan O'Donnell

  I'm working my way through Pickaxe 1.9, and I'm a bit confused by constant-lookup in instance/class_eval blocks. I'm using 1.9.2. It seems that Ruby handles constant-lookup in *_eval blocks the same way it does method-lookup: look for a definition in receiver.singleton_class (plus mixins); then in receiver.singleton_class.superclass (plus mixins); then continue up the eigenchain until you get to #<Class:BasicObject>; whose superclass is Class; and then up the rest of the ancestor chain (including Object, which stores all the constants you define at the top-level), checking for mixins along the way Is this correct? The Pickaxe discussion is a bit terse. Some examples: class Foo CONST = 'Foo::CONST' class << self CONST = 'EigenFoo::CONST' end end Foo.instance_eval { CONST } # => 'EigenFoo::CONST' Foo.class_eval { CONST } # => 'EigenFoo::CONST', not 'Foo::CONST'! Foo.new.instance_eval { CONST } # => 'Foo::CONST' In the class_eval example, Foo-the-class isn't a stop along Foo-the-object's ancestor chain! And an example with mixins: module M CONST = "M::CONST" end module N CONST = "N::CONST" end class A include M extend N end A.instance_eval { CONST } # => "N::CONST", because N is mixed into A's eigenclass A.class_eval { CONST } # => "N::CONST", ditto A.new.instance_eval { CONST } # => "M::CONST", because A.new.class, A, mixes in M

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• ISO C++ forbids declaration of 'QPushButton' with no type in QT Creator

  - by Mohit Deshpande

  I am running QT Creator on a Linux Ubuntu 9.10 machine. I just got started with QT Creator, and I was going through the tutorials when this error popped up while I was trying to build my project: "ISO C++ forbids declaration of 'QPushButton' with no type". This problem appears in my header file: #ifndef MAINWINDOW_H #define MAINWINDOW_H #include <QtGui/QWidget> namespace Ui { class MainWindow; } class MainWindow : public QWidget { Q_OBJECT public: MainWindow(QWidget *parent = 0); ~MainWindow(); public slots: void addContact(); void submitContact(); void cancel(); private: Ui::MainWindow *ui; QPushButton *addButton; QPushButton *submitButton; QPushButton *cancelButton; QLineEdit *nameLine; QTextEdit *addressText; QMap<QString, QString> contacts; QString oldName; QString oldAddress; }; #endif // MAINWINDOW_H

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• leak in fgets when assigning to buffer

  - by monkeyking

  I'm having problems understanding why following code leaks in one case, and not in the other case. The difference is while(NULL!=fgets(buffer,length,file))//doesnt leak while(NULL!=(buffer=fgets(buffer,length,file))//leaks I thought it would be the same. Full code below. #include <stdio.h> #include <stdlib.h> #define LENS 10000 void no_leak(const char* argv){ char *buffer = (char *) malloc(LENS); FILE *fp=fopen(argv,"r"); while(NULL!=fgets(buffer,LENS,fp)){ fprintf(stderr,"%s",buffer); } fclose(fp); fprintf(stderr,"%s\n",buffer); free(buffer); } void with_leak(const char* argv){ char *buffer = (char *) malloc(LENS); FILE *fp=fopen(argv,"r"); while(NULL!=(buffer=fgets(buffer,LENS,fp))){ fprintf(stderr,"%s",buffer); } fclose(fp); fprintf(stderr,"%s\n",buffer); free(buffer); }

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• Main Function Error C++

  - by Arjun Nayini

  I have this main function: #ifndef MAIN_CPP #define MAIN_CPP #include "dsets.h" using namespace std; int main(){ DisjointSets s; s.uptree.addelements(4); for(int i=0; i<s.uptree.size(); i++) cout <<uptree.at(i) << endl; return 0; } #endif And the following class: class DisjointSets { public: void addelements(int x); int find(int x); void setunion(int x, int y); private: vector<int> uptree; }; #endif My implementation is this: void DisjointSets::addelements(int x){ for(int i=0; i<x; i++) uptree.push_back(-1); } //Given an int this function finds the root associated with that node. int DisjointSets::find(int x){ //need path compression if(uptree.at(x) < 0) return x; else return find(uptree.at(x)); } //This function reorders the uptree in order to represent the union of two //subtrees void DisjointSets::setunion(int x, int y){ } Upon compiling main.cpp (g++ main.cpp) I'm getting these errors: dsets.h: In function \u2018int main()\u2019: dsets.h:25: error: \u2018std::vector DisjointSets::uptree\u2019 is private main.cpp:9: error: within this context main.cpp:9: error: \u2018class std::vector \u2019 has no member named \u2018addelements\u2019 dsets.h:25: error: \u2018std::vector DisjointSets::uptree\u2019 is private main.cpp:10: error: within this context main.cpp:11: error: \u2018uptree\u2019 was not declared in this scope I'm not sure exactly whats wrong. Any help would be appreciated.

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• OpenGLES - Rendering a background image only once and not wiping it

  - by chaosbeaker

  Hello, first time asking a question here but been watching others answers for a while. My own question is one for improving the performance of my program. Currently I'm wiping the viewFrameBuffer on each pass through my program and then rendering the background image first followed by the rest of my scene. I was wondering how I go about rendering the background image once, and only wiping the rest of the scene for updating/re-rendering. I tried using a seperate buffer but I'm not sure how to present this new buffer to the render buffer. // Set the current EAGLContext and bind to the framebuffer. This will direct all OGL commands to the // framebuffer and the associated renderbuffer attachment which is where our scene will be rendered [EAGLContext setCurrentContext:context]; glBindFramebufferOES(GL_FRAMEBUFFER_OES, viewFramebuffer); // Define the viewport. Changing the settings for the viewport can allow you to scale the viewport // as well as the dimensions etc and so I'm setting it for each frame in case we want to change i glViewport(0, 0, screenBounds.size.width , screenBounds.size.height); // Clear the screen. If we are going to draw a background image then this clear is not necessary // as drawing the background image will destroy the previous image glClearColor(0.0f, 1.0f, 0.0f, 1.0f); glClear(GL_COLOR_BUFFER_BIT); // Setup how the images are to be blended when rendered. This could be changed at different points during your // render process if you wanted to apply different effects glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA); switch (currentViewInt) { case 1: { [background render:CGPointMake(240, 0) fromTopLeftBottomRightCenter:@"Bottom"]; // Other Rendering Code }} // Bind to the renderbuffer and then present this image to the current context glBindRenderbufferOES(GL_RENDERBUFFER_OES, viewRenderbuffer); [context presentRenderbuffer:GL_RENDERBUFFER_OES]; Hopefully by solving this I'll also be able to implement another buffer just for rendering particles as I can set them to always use a black background as their alpha source. Any help is greatly appreciated

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• Division by zero: Undefined Behavior or Implementation Defined in C and/or C++ ?

  - by SiegeX

  Regarding division by zero, the standards say: C99 6.5.5p5 - The result of the / operator is the quotient from the division of the first operand by the second; the result of the % operator is the remainder. In both operations, if the value of the second operand is zero, the behavior is undefined. C++03 5.6.4 - The binary / operator yields the quotient, and the binary % operator yields the remainder from the division of the first expression by the second. If the second operand of / or % is zero the behavior is undefined. If we were to take the above paragraphs at face value, the answer is clearly Undefined Behavior for both languages. However, if we look further down in the C99 standard we see the following paragraph which appears to be contradictory(1): C99 7.12p4 - The macro INFINITY expands to a constant expression of type float representing positive or unsigned infinity, if available; Do the standards have some sort of golden rule where Undefined Behavior cannot be superseded by a (potentially) contradictory statement? Barring that, I don't think it's unreasonable to conclude that if your implementation defines the INFINITY macro, division by zero is defined to be such. However, if your implementation does not define such a macro, the behavior is Undefined. I'm curious what the consensus on this matter for each of the two languages. Would the answer change if we are talking about integer division int i = 1 / 0 versus floating point division float i = 1.0 / 0.0 ? Note (1) The C++03 standard talks about the library which includes the INFINITY macro.

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• Modify the server side functions using jquery

  - by ant

  Hi, I am developing one website using cakephp and jquery technologies. Server-side there are some functions which handles sql queris. As per requirement I want to modify server side functions on client side using jquery AJAX call. E.g. : Below is the function on server side to modify users information. function modifyUser(username,userid) { //update query statements } Then jquery AJAX call will be like this : $.ajax({ url: 'users/modiyUser', success: function() { alert("Updation done") or any statements. } }); and I want to modify above i.e. server side function depending upon client input criteria. $.ajax({ function users/modiyUser(username,userid) { // I will write here any other statements which gives me some other output. } }); Above AJAX call syntax may not present, but i think you all understood what I am trying to do I simply wants to modify/override server side functions on client side. Please let me know is there any way to resolve above mentioned requirement. Thanks in adavance

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• OpenGL Nothing will Display

  - by m00st

  Why can't I get anything to display with this code? #include <iostream> #include "GL/glfw.h" #ifndef MAIN #define MAIN #include "GL/gl.h" #include "GL/glu.h" #endif using namespace std; void display(); int main() { int running = GL_TRUE; glfwInit(); if( !glfwOpenWindow( 640,480, 0,0,0,0,0,0, GLFW_WINDOW ) ) { glfwTerminate(); return 0; } while( running ) { //GL Code here display(); glfwSwapBuffers(); // Check if ESC key was pressed or window was closed running = !glfwGetKey( GLFW_KEY_ESC ) && glfwGetWindowParam( GLFW_OPENED ); } glfwTerminate(); return 0; } void display() { glClearColor(0, 0,0, 0.0f); glClear(GL_COLOR_BUFFER_BIT); glLoadIdentity(); gluLookAt(0, 0, 5, 0.0, 0.0, 0.0, 0, 1, 0); glScalef(1.0f, 1.0f, 1.0f); glTranslatef(0, 0, -2); glBegin(GL_POLYGON); glColor3f(1.0, 0.2, 0.2); glVertex3f(0.25, 0.25, 0.0); glVertex3f(0.75, 0.25, 0.0); glVertex3f(0.75, 0.75, 0.0); glVertex3f(0.25, 0.75, 0.0); glEnd(); glFlush(); }

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• Using libgrib2c in c++ application, linker error "Undefined reference to..."

  - by Rich

  EDIT: If you're going to be doing things with GRIB files I would recommend the GDAL library which is backed by the Open Source Geospatial Foundation. You will save yourself a lot of headache :) I'm using Qt creator in Ubuntu creating a c++ app. I am attempting to use an external lib, libgrib2c.a, that has a header grib2.h. Everything compiles, but when it tries to link I get the error: undefined reference to 'seekgb(_IO_FILE*, long, long, long*, long*) I have tried wrapping the header file with: extern "C"{ #include "grib2.h" } But it didn't fix anything so I figured that was not my problem. In the .pro file I have the line: include($${ROOT}/Shared/common/commonLibs.pri) and in commonLibs.pri I have: INCLUDEPATH+=$${ROOT}/external_libs/g2clib/include LIBS+=-L$${ROOT}/external_libs/g2clib/lib LIBS+=-lgrib2c I am not encountering an error finding the library. If I do a nm command on the libgrib2c.a I get: nm libgrib2c.a | grep seekgb seekgb.o: 00000000 T seekgb And when I run qmake with the additional argument of LIBS+=-Wl,--verbose I can find the lib file in the output: attempt to open /usr/lib/libgrib2c.so failed attempt to open /usr/lib/libgrib2c.a failed attempt to open /mnt/sdb1/ESMF/App/ESMF_App/../external_libs/linux/qwt_6.0.2/lib/libgrib2c.so failed attempt to open /mnt/sdb1/ESMF/App/ESMF_App/../external_libs/linux/qwt_6.0.2/lib/libgrib2c.a failed attempt to open ..//Shared/Config/lib/libgrib2c.so failed attempt to open ..//Shared/Config/lib/libgrib2c.a failed attempt to open ..//external_libs/libssh2/lib/libgrib2c.so failed attempt to open ..//external_libs/libssh2/lib/libgrib2c.a failed attempt to open ..//external_libs/openssl/lib/libgrib2c.so failed attempt to open ..//external_libs/openssl/lib/libgrib2c.a failed attempt to open ..//external_libs/g2clib/lib/libgrib2c.so failed attempt to open ..//external_libs/g2clib/lib/libgrib2c.a succeeded Although it doesn't show any of the .o files in the library is this because it is a c library in my c++ app? in the .cpp file that I am trying to use the library I have: #include "gribreader.h" #include <stdio.h> #include <stdlib.h> #include <external_libs/g2clib/include/grib2.h> #include <Shared/logging/Logger.hpp> //------------------------------------------------------------------------------ /// Opens a GRIB file from disk. /// /// This function opens the grib file and searches through it for how many GRIB /// messages are contained as well as their starting locations. /// /// \param a_filePath. The path to the file to be opened. /// \return True if successful, false if not. //------------------------------------------------------------------------------ bool GRIBReader::OpenGRIB(std::string a_filePath) { LOG(notification)<<"Attempting to open grib file: "<< a_filePath; if(isOpen()) { CloseGRIB(); } m_filePath = a_filePath; m_filePtr = fopen(a_filePath.c_str(), "r"); if(m_filePtr == NULL) { LOG(error)<<"Unable to open file: " << a_filePath; return false; } LOG(notification)<<"Successfully opened GRIB file"; g2int currentMessageSize(1); g2int seekPosition(0); g2int lengthToBeginningOfGrib(0); g2int seekLength(32000); int i(0); int iterationLimit(300); m_GRIBMessageLocations.clear(); m_GRIBMessageSizes.clear(); while(i < iterationLimit) { seekgb(m_filePtr, seekPosition, seekLength, &lengthToBeginningOfGrib, &currentMessageSize); if(currentMessageSize != 0) { LOG(verbose) << "Adding GRIB message location " << lengthToBeginningOfGrib << " with length " << currentMessageSize; m_GRIBMessageLocations.push_back(lengthToBeginningOfGrib); m_GRIBMessageSizes.push_back(currentMessageSize); seekPosition = lengthToBeginningOfGrib + currentMessageSize; LOG(verbose) << "GRIB seek position moved to " << seekPosition; } else { LOG(notification)<<"End of GRIB file found, after "<< i << " GRIB messages."; break; } } if(i >= iterationLimit) { LOG(warning) << "The iteration limit of " << iterationLimit << "was reached while searching for GRIB messages"; } return true; } And the header grib2.h is as follows: #ifndef _grib2_H #define _grib2_H #include<stdio.h> #define G2_VERSION "g2clib-1.4.0" #ifdef __64BIT__ typedef int g2int; typedef unsigned int g2intu; #else typedef long g2int; typedef unsigned long g2intu; #endif typedef float g2float; struct gtemplate { g2int type; /* 3=Grid Defintion Template. */ /* 4=Product Defintion Template. */ /* 5=Data Representation Template. */ g2int num; /* template number. */ g2int maplen; /* number of entries in the static part */ /* of the template. */ g2int *map; /* num of octets of each entry in the */ /* static part of the template. */ g2int needext; /* indicates whether or not the template needs */ /* to be extended. */ g2int extlen; /* number of entries in the template extension. */ g2int *ext; /* num of octets of each entry in the extension */ /* part of the template. */ }; typedef struct gtemplate gtemplate; struct gribfield { g2int version,discipline; g2int *idsect; g2int idsectlen; unsigned char *local; g2int locallen; g2int ifldnum; g2int griddef,ngrdpts; g2int numoct_opt,interp_opt,num_opt; g2int *list_opt; g2int igdtnum,igdtlen; g2int *igdtmpl; g2int ipdtnum,ipdtlen; g2int *ipdtmpl; g2int num_coord; g2float *coord_list; g2int ndpts,idrtnum,idrtlen; g2int *idrtmpl; g2int unpacked; g2int expanded; g2int ibmap; g2int *bmap; g2float *fld; }; typedef struct gribfield gribfield; /* Prototypes for unpacking API */ void seekgb(FILE *,g2int ,g2int ,g2int *,g2int *); g2int g2_info(unsigned char *,g2int *,g2int *,g2int *,g2int *); g2int g2_getfld(unsigned char *,g2int ,g2int ,g2int ,gribfield **); void g2_free(gribfield *); /* Prototypes for packing API */ g2int g2_create(unsigned char *,g2int *,g2int *); g2int g2_addlocal(unsigned char *,unsigned char *,g2int ); g2int g2_addgrid(unsigned char *,g2int *,g2int *,g2int *,g2int ); g2int g2_addfield(unsigned char *,g2int ,g2int *, g2float *,g2int ,g2int ,g2int *, g2float *,g2int ,g2int ,g2int *); g2int g2_gribend(unsigned char *); /* Prototypes for supporting routines */ extern double int_power(double, g2int ); extern void mkieee(g2float *,g2int *,g2int); void rdieee(g2int *,g2float *,g2int ); extern gtemplate *getpdstemplate(g2int); extern gtemplate *extpdstemplate(g2int,g2int *); extern gtemplate *getdrstemplate(g2int); extern gtemplate *extdrstemplate(g2int,g2int *); extern gtemplate *getgridtemplate(g2int); extern gtemplate *extgridtemplate(g2int,g2int *); extern void simpack(g2float *,g2int,g2int *,unsigned char *,g2int *); extern void compack(g2float *,g2int,g2int,g2int *,unsigned char *,g2int *); void misspack(g2float *,g2int ,g2int ,g2int *, unsigned char *, g2int *); void gbit(unsigned char *,g2int *,g2int ,g2int ); void sbit(unsigned char *,g2int *,g2int ,g2int ); void gbits(unsigned char *,g2int *,g2int ,g2int ,g2int ,g2int ); void sbits(unsigned char *,g2int *,g2int ,g2int ,g2int ,g2int ); int pack_gp(g2int *, g2int *, g2int *, g2int *, g2int *, g2int *, g2int *, g2int *, g2int *, g2int *, g2int *, g2int *, g2int *, g2int *, g2int *, g2int *, g2int *, g2int *, g2int *, g2int *); #endif /* _grib2_H */ I have been scratching my head for two days on this. If anyone has an idea on what to do or can point me in some sort of direction, I'm stumped. Also, if you have any comments on how I can improve this post I'd love to hear them, kinda new at this posting thing. Usually I'm able to find an answer in the vast stores of knowledge already contained on the web.

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• Hide struct definition in static library.

  - by BobMcLaury

  Hi, I need to provide a C static library to the client and need to be able to make a struct definition unavailable. On top of that I need to be able to execute code before the main at library initialization using a global variable. Here's my code: private.h #ifndef PRIVATE_H #define PRIVATE_H typedef struct TEST test; #endif private.c (this should end up in a static library) #include "private.h" #include <stdio.h> struct TEST { TEST() { printf("Execute before main and have to be unavailable to the user.\n"); } int a; // Can be modified by the user int b; // Can be modified by the user int c; // Can be modified by the user } TEST; main.c test t; int main( void ) { t.a = 0; t.b = 0; t.c = 0; return 0; } Obviously this code doesn't work... but show what I need to do... Anybody knows how to make this work? I google quite a bit but can't find an answer, any help would be greatly appreciated. TIA!

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• Changing Apache2.2.11 httpd.conf has no effect

  - by Adrian

  Hi, Hopefully someone can help here. I recently installed wampserver ver 2.0 with Apache ver 2.2.11. My issue is, I have some large php scripts which timeout at the default 5 min (300 sec) browser limit (I'm using ie8). It is critcal I get this limit extended. I have tried changing the httpd.conf file to include the following: TimeOut 1200 My objective was to set the timeout at 1200 seconds, or 20 min. I had just chosen a random location to place this directive within the httpd.conf file as I cannot locate any documentation to suggest it belongs in a specific place within the file. Regardless, the changes I make appear in the httpd.conf file that can be found in the system tray for wampserver, however they have no effect - the browser still times out after 5 minutes. I thought perhaps I had the capitals incorrect, so I changed to: Timeout 1200 This change had no effect either. Can someone please help, this is very frustrating. Maybe the command can only be used within a specific module? If so, I have no idea which one, nor do I know the syntax to specify this. Regards Adrian.

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• Where is the taglib definition of PrimeFaces 4?

  - by Michael Wölm

  I am looking around how to define custom components in JSF. According to the Java EE tutorial, any custom component needs to be described in a taglib. When I take a look into the PrimeFaces source, I cannot find any taglib file or any hint where the namespace is bound and the available components are defined. I am adding primefaces jar to my dependencies, adding xmlns:p="http://primefaces.org/ui to the xml namespace, defining some primfaces components on my page and it works... Ok, but neither I can find the related taglib in the source or binary package nor my IDE (IntelliJ) is able to find where "xmlns:p="http://primefaces.org/ui" is pointing to. Therefore, code completion is also not possible. (all other mojarra taglibs are found.) Is it possible that PrimeFaces is defining the taglib via annotations directly in Java classes or is it generating it during runtime? I can easily find the UIComponents, primefaces defines in its source, but the configuration of the taglib seems to be missing. I am sure I just don't know how PrimeFaces is doing it, but the javaeetutorial is not describing any other opportunity than defining a ...-taglib.xml

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• JavaScript: how to create a JS event that requires 2 seperate JS files to be loaded first while down

  - by Teddyk

  I want to perform asynchronous JavaScript downloads of two files that have dependencies attached to them. // asynch download of jquery and gmaps function addScript(url) { var script = document.createElement('script'); script.src = url; document.getElementsByTagName('head')[0].appendChild(script); } addScript('http://google.com/gmaps.js'); addScript('http://jquery.com/jquery.js'); // define some function dependecies function requiresJQuery() { ... } function requiresGmaps() { ... } function requiresBothJQueryGmaps() { ... } // do some work that has no dependencies on either JQuery or Google maps ... // QUESTION - Pseudo code below // now call a function that requires Gmaps to be loaded if (GmapsIsLoaded) { requiresGmaps(); } // QUESTION - Pseudo code below // then do something that requires both JQuery & Gmaps (or wait until they are loaded) if (JQueryAndGmapsIsLoaded) { requiresBothJQueryGmaps(); } Question: How can I create an event to indicate when: JQuery is loaded? Google Maps is loaded JQuery & Google Maps are both loaded?

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• methods of metaclasses on class instances.

  - by Stefano Borini

  I was wondering what happens to methods declared on a metaclass. I expected that if you declare a method on a metaclass, it will end up being a classmethod, however, the behavior is different. Example >>> class A(object): ... @classmethod ... def foo(cls): ... print "foo" ... >>> a=A() >>> a.foo() foo >>> A.foo() foo However, if I try to define a metaclass and give it a method foo, it seems to work the same for the class, not for the instance. >>> class Meta(type): ... def foo(self): ... print "foo" ... >>> class A(object): ... __metaclass__=Meta ... def __init__(self): ... print "hello" ... >>> >>> a=A() hello >>> A.foo() foo >>> a.foo() Traceback (most recent call last): File "<stdin>", line 1, in <module> AttributeError: 'A' object has no attribute 'foo' What's going on here exactly ? edit: bumping the question

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• Visual studio erroneous errors when building a website?

  - by Curtis White

  Visual Studio 2008 shows a lot of erroneous errors when building a website (not a web project) in the errors list. These errors are usually corrected (removed) when I rebuild the site a couple times but they cost me wasted time. Is there anyway to hide the erroneous errors? Update: I've decided to look into this to see if I could reproduce it. This is the exact behavior I am seeing, using the website model, I type some invalid syntax on a page. The errors list fills up with errors. I correct the error and the errors list does not update. I build the project and the errors list still shows the errors but the build shows as build completed. I build the project a second time and the errors list is cleared. My question is there anyway to make the errors list clear on the first build? I thought it might have something to do with page build vs website build but it seems to make no difference. I am not using any third party dlls on this website.

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• c++ File input/output

  - by Myx

  Hi: I am trying to read from a file using fgets and sscanf. In my file, I have characters on each line of the while which I wish to put into a vector. So far, I have the following: FILE *fp; fp = fopen(filename, "r"); if(!fp) { fprintf(stderr, "Unable to open file %s\n", filename); return 0; } // Read file int line_count = 0; char buffer[1024]; while(fgets(buffer, 1023, fp)) { // Increment line counter line_count++; char *bufferp = buffer; ... while(*bufferp != '\n') { char *tmp; if(sscanf(bufferp, "%c", tmp) != 1) { fprintf(stderr, "Syntax error reading axiom on " "line %d in file %s\n", line_count, filename); return 0; } axiom.push_back(tmp); printf("put %s in axiom vector\n", axiom[axiom.size()-1]); // increment buffer pointer bufferp++; } } my axiom vector is defined as vector<char *> axiom;. When I run my program, I get a seg fault. It happens when I do the sscanf. Any suggestions on what I'm doing wrong?

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• How to solve generic algebra using solver/library programmatically? Matlab, Mathematica, Wolfram etc?

  - by DevDevDev

  I'm trying to build an algebra trainer for students. I want to construct a representative problem, define constraints and relationships on the parameters, and then generate a bunch of Latex formatted problems from the representation. As an example: A specific question might be: If y < 0 and (x+3)(y-5) = 0, what is x? Answer (x = -3) I would like to encode this as a Latex formatted problem like. If $y<0$ and $(x+constant_1)(y+constant_2)=0$ what is the value of x? Answer = -constant_1 And plug into my problem solver constant_1 > 0, constant_1 < 60, constant_1 = INTEGER constant_2 < 0, constant_2 > -60, constant_2 = INTEGER Then it will randomly construct me pairs of (constant_1, constant_2) that I can feed into my Latex generator. Obviously this is an extremely simple example with no real "solving" but hopefully it gets the point across. Things I'm looking for ideally in priority order * Solve algebra problems * Definition of relationships relatively straight forward * Rich support for latex formatting (not just writing encoded strings) Thanks!

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• How to inherit the current path when invoking Maven's exec-maven-plugin?

  - by wishihadabettername

  I have an <exec-maven-plugin> which calls an external command (in this case, svnversion). The command is in the path for the current user. However, when a separate shell is spawned by the plugin, the path is not initialized. I don't want to hardcode or define a variable for each external command (there would be too much to maintain, especially that there are both Windows and *nix users). My pom.xml contains the following: <plugin> <groupId>org.codehaus.mojo</groupId> <artifactId>exec-maven-plugin</artifactId> <version>1.1</version> <executions> <execution> <id>svnversion-exec</id> <phase>process-resources</phase> <goals> <goal>exec</goal> </goals> <configuration> <executable>svnversion</executable> <arguments> <argument><![CDATA[ >version.txt ]]></argument> </arguments> </configuration> </execution> </executions> </plugin> Currently I get the following output: [INFO] [exec:exec {execution: svnversion-exec}] 'svnversion' is not recognized as an internal or external command, operable program or batch file. [ERROR] BUILD ERROR: Result of cmd.exe /X /C "svnversion >version.txt" execution is: '1'. Thank you!

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• Learning C++ as a Perl programmer

  - by meneldor

  Hello all, I'm a Perl5 programmer for 7 years and I'm trying to learn C++ now. Some of the c++ syntax is hard for me to understand and to think in c++ way. For example: In perl you can mix the data in the arrays @array = (1,"string",5.355); You can assign any value to a scalar variable: $var = 1; $var = "string"; $var = \$reference_to_scalar; There are many examples. The friend of mine recommend me the book "Thinking of C++" by Bruce Eckel, but I haven't any C background and it's hard for me to understand some things. So my question is - could you recommend me a book for this situation. I don't want to learn C. I understand OOP (I'm getting more familiar with C++ oop aswell), I understand the point of the pointers(and some arithmetic) and references(widely used in perl). I dont need some of the manuals for dummies (what is int,bool,double,if,while), I just need a direction how to learn C++ from my point of perl programmer, because I,m sure that there are many like me. Thank you in advance.

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• How to easily map c++ enums to strings

  - by Roddy

  I have a bunch of enum types in some library header files that I'm using, and I want to have a way of converting enum values to user strings - and vice-versa. RTTI won't do it for me, because the 'user strings' need to be a bit more readable than the enumerations. A brute force solution would be a bunch of functions like this, but I feel that's a bit too C-like. enum MyEnum {VAL1, VAL2,VAL3}; String getStringFromEnum(MyEnum e) { switch e { case VAL1: return "Value 1"; case VAL2: return "Value 2"; case VAL1: return "Value 3"; default: throw Exception("Bad MyEnum"); } } I have a gut feeling that there's an elegant solution using templates, but I can't quite get my head round it yet. UPDATE: Thanks for suggestions - I should have made clear that the enums are defined in a third-party library header, so I don't want to have to change the definition of them. My gut feeling now is to avoid templates and do something like this: char * MyGetValue(int v, char *tmp); // implementation is trivial #define ENUM_MAP(type, strings) char * getStringValue(const type &T) \ { \ return MyGetValue((int)T, strings); \ } ; enum eee {AA,BB,CC}; - exists in library header file ; enum fff {DD,GG,HH}; ENUM_MAP(eee,"AA|BB|CC") ENUM_MAP(fff,"DD|GG|HH") // To use... eee e; fff f; std::cout<< getStringValue(e); std::cout<< getStringValue(f);

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• How can I have sub-elements of a complex/mixed type with unrestricted order and count?

  - by mbmcavoy

  I am working with XML where some elements will contain text with additional markup. This is similar to this example at W3Schools. However, I need the markup tags to be able to appear in any order and possibly more than once. To modify their example for illustration: <letter> Dear Mr.<name>John Smith</name>. Your order <orderid>1032</orderid> will be shipped on <shipdate>2001-07-13</shipdate>. Thank you, <name>Bob Adams</name> </letter> None of the options presented by W3Schools (on the page following the linked example) allow this XML due to the second <name> element. Their explanation of the "indicators" and my testing are consistent. <xs:sequence> - violates the element order <xs:choice> - more than one kind of element is used. <xs:all> - maxOccurs is restricted to "1". This seems like it should be basic, after all, XHTML allows such things. How do I define my schema to allow this?

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• NHibernate query against the key field of a dictionary (map)

  - by Carl Raymond

  I have an object model where a Calendar object has an IDictionary<MembershipUser, Perms> called UserPermissions, where MembershipUser is an object, and Perms is a simple enumeration. This is in the mapping file for Calendar as <map name="UserPermissions" table="CalendarUserPermissions" lazy="true" cascade="all"> <key column="CalendarID"/> <index-many-to-many class="MembershipUser" column="UserGUID" /> <element column="Permissions" type="CalendarPermission" not-null="true" /> </map> Now I want to execute a query to find all calendars for which a given user has some permission defined. The permission is irrelevant; I just want a list of the calendars where a given user is present as a key in the UserPermissions dictionary. I have the username property, not a MembershipUser object. How do I build that using QBC (or HQL)? Here's what I've tried: ISession session = SessionManager.CurrentSession; ICriteria calCrit = session.CreateCriteria<Calendar>(); ICriteria userCrit = calCrit.CreateCriteria("UserPermissions.indices"); userCrit.Add(Expression.Eq("Username", username)); return calCrit.List<Calendar>(); This constructed invalid SQL -- the WHERE clause contained WHERE membership1_.Username = @p0 as expected, but the FROM clause didn't include the MemberhipUsers table. Also, I really had to struggle to learn about the .indices notation. I found it by digging through the NHibernate source code, and saw that there's also .elements and some other dotted notations. Where's a reference to the allowed syntax of an association path? I feel like what's above is very close, and just missing something simple.

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• How to prepare data for display on a silverlight chart using WCF RIA Services + Entity Framework

  - by Banford

  I've used WCF RIA services with Entity Framework to build a simple application which can display and updates data about school courses. This was done by following the Microsoft tutorials. Now I would like to have a chart which shows a count for how many courses are on a key stage. Example: Key Stage 3 - 20 courses Key Stage 4 - 32 courses Key Stage 5 - 12 courses Displayed on any form of chart. I have no problem binding data to the chart in XAML. My problem is that I do not know how to correct way of getting the data into that format. The generated CRUD methods are basic. I have a few thoughts about possible ways, but don't know which is correct, they are: Create a View in SQL server and map this to a separate Entity in the Entity Data Model. Generating new CRUD methods for this automatically. Customise the read method in the existing DomainService using .Select() .Distinct() etc. Don't know this syntax very well labda expressions/LINQ??? what is it? Any good quickstarts on it? Create a new class to store only the data required and create a read method for it. Tried this but didn't know how to make it work without a matching entity in the entity model. Something I am not aware of. I'm very new to this and struggling with the concepts so if there are useful blogs or documentation I've missed feel free to point me towards them. But I'm unsure of the terminology to use in my searches at the moment.

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• Checking multiple conditions in Ruby (within Rails, which may not matter)

  - by Ev

  Hello rubyists and railers, I have a method which checks over a params hash to make sure that it contains certain keys, and to make sure that certain values are set within a certain range. This is for an action that responds to a POST query by an iPhone app. Anyway, this method is checking for about 10 different conditions - any of which will result in an HTTP error being returned (I'm still considering this, but possibly a 400: bad request error). My current syntax is basically this (paraphrased): def invalid_submission_params?(params) [check one] or [check two] or [check three] or [check four] etc etc end Where each of the check statements returns true if that particular parameter check results in an invalid parameter set. I call it as a before filter with params[:submission] as the argument. This seems a little ugly (all the strung together or statements). Is there a better way? I have tried using case but can't see a way to make it more elegant. Or, perhaps, is there a rails method that lets me check the incoming params hash for certain conditions before handing control off to my action method?

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• error: invalid type argument of '->' (have 'struct node')

  - by Roshan S.A

  Why cant i access the pointer "Cells" like an array ? i have allocated the appropriate memory why wont it act like an array here? it works like an array for a pointer of basic data types. #include<stdio.h> #include<stdlib.h> #include<ctype.h> #define MAX 10 struct node { int e; struct node *next; }; typedef struct node *List; typedef struct node *Position; struct Hashtable { int Tablesize; List Cells; }; typedef struct Hashtable *HashT; HashT Initialize(int SIZE,HashT H) { int i; H=(HashT)malloc(sizeof(struct Hashtable)); if(H!=NULL) { H->Tablesize=SIZE; printf("\n\t%d",H->Tablesize); H->Cells=(List)malloc(sizeof(struct node)* H->Tablesize); should it not act like an array from here on? if(H->Cells!=NULL) { for(i=0;i<H->Tablesize;i++) the following lines are the ones that throw the error { H->Cells[i]->next=NULL; H->Cells[i]->e=i; printf("\n %d",H->Cells[i]->e); } } } else printf("\nError!Out of Space"); } int main() { HashT H; H=Initialize(10,H); return 0; } The error I get is as in the title-error: invalid type argument of '->' (have 'struct node').

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