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• CSV parser in C++

  - by User1

  All I need is a good CSV file parser for C++. At this point it can really just be a comma-delimited parser (ie don't worry about escaping new lines and commas). The main need is a line-by-line parser that will return a vector for the next line each time the method is called. I found this article which looks quite promising: http://www.boost.org/doc/libs/1_35_0/libs/spirit/example/fundamental/list_parser.cpp I've never used Boost's Spirit, but am willing to try it. Is it overkill/bloated or is it fast and efficient? Does anyone have faster algorithms using STL or anything else? Thanks!

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• What is a good standard for code width?

  - by BillyONeal

  Hello everyone :) I've heard in several places that it's bad to have code that is too wide onscreen. For example: for (std::vector<EnumServiceInformation>::const_iterator currentService = services.begin(); currentService != services.end(); currentService++) However, I've heard many arguments for 80 character wide limits. I'm assuming this 80 character limit comes from the traditional command prompt, which is typically 80 characters wide. However -- most of us are working on something much better than a typical command prompt, and I feel that using an 80 character limit encourages use of variable names that are far too short and do not describe what the variable is used for. What is a reasonable limit for a new project with no existing coding width standard?

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• Filtering spectrum using FIR filters

  - by Alex Hoppus

  If i have signal values x[T] and filter coefficients b[i], i can perform filtering using convolution. Suppose i have spectrum of x (after FFT) and i need to perform filtering using filters coefficients, how can i perform this? I heard that in frequency domain it will be multiplying, rather than convolution (time domain). But i can't find an equation to use it. I have 614000 values in y = fft(x[T]) vector and 119 filter coefficients (generated using fdatool), i can't multiply them directly ... Thanks.

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• C++ - Where to code a member function for an inherited object.

  - by Francisco P.

  Hello! I have a few classes (heat, gas, contact, pressure) inheriting from a main one (sensor). I have a need to store them in a vector<Sensor *> (part of the specification). At some point in time, I need to call a function that indiscriminately stores those Sensor *. (also part of the specification, not open for discussion) Something like this: for(size_t i = 0; i < Sensors.size(); ++i) Sensors[i]->storeSensor(os) //os is an ofstream kind of object, passed onwards by reference Where and how shall storeSensor be defined? Is there any simple way to do this or will I need to disregard the specification? Mind you, I'm a beginner! Thanks for your time!

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• allocator with no template

  - by Merni

  Every stl container take an allocator as a second object, template < class T, class Allocator = allocator<T> > class vector; If you write your own class It is possible to use your own allocator. But is it possible to write your own allocator without using templates? For example, writing this function is not easy if you are not allowed to use templates pointer allocate(size_type n, const_pointer = 0) { void* p = std::malloc(n * sizeof(T)); if (!p) throw std::bad_alloc(); return static_cast<pointer>(p); } Because how could you know the size of T?

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• Collection type generated by for with yield

  - by Jesper

  When I evaluate a for in Scala, I get an immutable IndexedSeq (a collection with array-like performance characteristics, such as efficient random access): scala> val s = for (i <- 0 to 9) yield math.random + i s: scala.collection.immutable.IndexedSeq[Double] = Vector(0.6127056766832756, 1.7137598183155291, ... Does a for with a yield always return an IndexedSeq, or can it also return some other type of collection class (a LinearSeq, for example)? If it can also return something else, then what determines the return type, and how can I influence it? I'm using Scala 2.8.0.RC3.

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• Some exam questions about C++ vectors and arrays...

  - by xbonez

  Hey guys, I have a CS exam tomorrow. Just want to get a few questions cleared up. Thanks a lot, and I really appreciate the help. Que 1. What are parallel vectors? Vectors of the same length that contain data that is meant to be processed together Vectors that are all of the same data type Vectors that are of the same length Any vector of data type parallel Que 2. Arrays are faster and more efficient than vectors. True False Que 3. Arrays can be a return type of a function call. True False Que 4. Vectors can be a return type of a function call. True False

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• Unexpected result from reduce function

  - by StackedCrooked

  I would like to get the smallest element from a vector. For this I use combine the reduce and min functions. However, when providing my own implementation of min I get unexpected results: user=> (reduce (fn [x y] (< x y) x y) [1 2 3 2 1 0 1 2]) 2 user=> (reduce min [1 2 3 2 1 0 1 2 3]) 0 The reduce with standard min returns 0 as expected. However, when I provide my own implementation it returns 2. What am I doing wrong?

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• Best way to copy large amount of data between partitions

  - by skinp

  I'm looking to transfer data across 2 lv of an HP-UX server. I have a couple of those transfers to do, some of which are mostly binary (Oracle tablespace...) and some others are more text files (logs...). Used data size of the volumes is between 100Gb and 1Tb. Also, I will be changing the block size from 1K to 8K on some of these partitions... Things I'm looking for: Guarantees data integrity Fastest data transfer speed Keeps file ownership and permissions Right now, I've thought about dd, cp and rsync, but I'm not sure on the best one to use and the best way to use them...

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• Determining if two rays intersect

  - by Faken

  I have two rays on a 2D plane that extend to infinity but both have a starting point. They are both described by a starting point and a vector in the direction of the ray extending to infinity. I want to find out if the two rays intersect but i don't need to know where they intersect (its part of a collision detection algorithm). Everything i have looked at so far describes finding the intersection point of two lines or line segments. Anyone know a fast algorithm to solve this?

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• Designing entire webpages as SVG files

  - by user1311390

  Disclaimer I realize that given the absurdity of the title, this sounds like a troll. However, it's a genuine question. My background involves OpenGL / x86 assembly. I've recently started learning web programming. I really like SVG + CSS, and was wondering -- why do people not design entire webpages in SVG? Context SVG provides beautiful primitive: quadratic + cubic bezier curves; lines + filling -- all as vector graphics SVG provides text SVG provides affine transformations Questions Are there examples of people designing entire websites as a giant SVG file? If not, what the limitations? Are there performance hits when using SVG primitives as opposed to divs/tables?

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• Can I use MFC objects in STL containers?

  - by Jesse Stimpson

  The following code doesn't compile for me in MSVC2005: std::vector<CMenu> vec(10); CMenu is an MFC menu object (such as a context menu). Through some testing I learned that CMenu does not have a public copy constructor. To do what I wanted to do, I needed to use a dynamic array. CMenu* menus = new CMenu[10]; // ... delete [] menus; Of course, now I've lost all the benefits of using an STL container. Do I have any other options?

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• Javascript function returning number with two decimals...?

  - by muzzledBYbrass

  I have a function to return points along a line and my return comes back with two decimal points...? For example, a return of my variable px will be something like -88.4029.032940598. vx is the x vector and mult is the distance of the line plus distance to calculate the point. Here is the operation that is returning these values: var mult = parseFloat(mag + theUnit); var px = coord_one.x_point + (vx * mult); console.log(px); Never have seen this before- I appreciate any and all help!

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• C++ Array of Variable sized Arrays

  - by adam

  I am very new to C++ and I realise the following is not necessarily as easy as I'd like it to be, but I'd really appreciate a more expert opinion. I am essentially trying to achieve a dynamic iteration over a variable sized array of variable sized arrays similar to the following. String *2d_array[][] = {{"A1","A2"},{"B1","B2","B3"},{"C1"}}; for (int i=0; i<2d_array.length; i++) { for (int j=0; j<2d_array[i].length; j++) { print(2d_array[i][j]); } } Is there a reasonable way to do this? Perhaps by using a vector, or another struct? Thanks :)

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• Why am I not getting correct result when I calculate exponent with ^ in C++?

  - by xbonez

  I am using Bode's formuala to calculate distance of nth planet from sun dist = (4 + 3*(2^(n-2)))/10 If I calculate the distance this way, I get the right values: dist[2] = ((4 + 3*1)/10.0) ; dist[3] = ((4 + 3*2)/10.0) ; dist[4] = ((4 + 3*4)/10.0) ; But doing it this way, gives me incorrect values: vector <double> dist(5); for (unsigned int i = 2; i < 5; i++) { dist[i] = ((4 + 3*(2^(3-2)))/10.0) ; } Why so?

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• E: Sub-process /usr/bin/dpkg returned an error code (100)

  - by user67011

  Hello, I am running on xen, Debian 5.0-i386-default. I haven't touched my vps in 2 months then last night I ran the following command: myserver:/usr/bin# apt-get upgrade Reading package lists... Done Building dependency tree Reading state information... Done The following packages have been kept back: makepasswd The following packages will be upgraded: libc6 libc6-dev libc6-xen libmysqlclient15off locales mysql-client mysql-client-5.0 mysql- common mysql-server mysql-server-5.0 10 upgraded, 0 newly installed, 0 to remove and 1 not upgraded. Need to get 0B/50.1MB of archives. After this operation, 483kB of additional disk space will be used. Do you want to continue [Y/n]? y Preconfiguring packages ... E: Sub-process /usr/bin/dpkg returned an error code (100) I googled and it seems to be a permission thing for "dpkg". However, I cd into /usr/bin and there's no dpkg binary!!! Please help thanks

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• WSO2 Installation Stops

  - by Nik

  I am only trying to get WSO2 Data Services to start up on an Ubuntu 10.04 LTS server. I have installed Java, set the JAVA_HOME environment variable, and download the binary distribution from WSO2. When I run /opt/wso2dataservices-2.6.2/bin/wso2server.sh, everything seems to start up fine and I can start to navigate to the page. The problem is a few seconds later, the console says Killed and everything stops. Does anybody have any ideas for how I can figure out what's going on? Edit: It seems to stop when I try to access the page, but not on its own.

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• HELP!! Implementing a search to match the specified author and displaying a book by the specified publisher

  - by Brian

  Hey guys! So i'm having problems with my assignment. I successfully got it to run multiple last names by the author, but now, I need to find all books by author, which means searching the collection for all books that match the specified author and I also need to find all books by publisher, which displays a list of books by the specified publisher. How would I implement this? Would I use string or vector? Any help will be much appreciated!

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• How to check whether iterators form a contiguous memory zone?

  - by Vincent

  I currently have the following function to read an array or a vector of raw data (_readStream is a std::ifstream) : template<typename IteratorType> inline bool MyClass::readRawData( const IteratorType& first, const IteratorType& last, typename std::iterator_traits<IteratorType>::iterator_category* = nullptr ) { _readStream.read(reinterpret_cast<char*>(&*first), (last-first)*sizeof(*first)); return _readStream.good(); } First question : does this function seem ok for you ? As we read directly a block of memory, it will only work if the memory block from first to last is contiguous in memory. How to check that ?

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• Twin edges - Half edge data structure

  - by Pradeep Kumar

  I have implemented a Half-edge data structure for loading 3d objects. I find that the part of assigning twin/pair edges takes the longest computation time (especially for objects which have hundreds of thousands half edges). The reason is that I use nested loops to accomplish this. Is there a simpler and efficient way of doing this? Below is the code which I've written. HE is the half-edge data structure. hearr is a vector containing all the half edges. vert is the starting vertex and end is the ending vertex. Thanks!! HE *e1,*e2; for(size_t i=0;i<hearr.size();i++){ e1=hearr[i]; for(size_t j=1;j<hearr.size();j++){ e2=hearr[j]; if((e1->vert==e2->end)&&(e2->vert==e1->end)){ e1->twin=e2; e2->twin=e1; } } }

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• Run a script as root from apache

  - by Lord Loh.

  I would like to update my hosts file and restart dnsmasq from a web interface (php/apache2). I tried playing around with suid bits (the demonstaration). I have both apache and dnsmasq running on an EC2 instance. I understand that Linux ignores the setuid bit on text scripts, but works on binary files. (Have I got something wrong?). I added exec("whoami"); to the example C program in Wikipedia. Although the effective UID of the C program is 0, whoami does not return root :-( I would thoroughly like to avoid echo password | sudo service dnsmasq restart or adding apache to the sudoers without password! Is there a way out? How does webmin do such things?

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• How to retrieve all keys (or values) from a std::map?

  - by Owen

  This is one of the possible ways I come out: struct RetrieveKey { template <typename T> typename T::first_type operator()(T keyValuePair) const { return keyValuePair.first; } }; map<int, int> m; vector<int> keys; // Retrieve all keys transform(m.begin(), m.end(), back_inserter(keys), RetrieveKey()); // Dump all keys copy(keys.begin(), keys.end(), ostream_iterator<int>(cout, "\n")); Of course, we can also retrieve all values from the map by defining another functor RetrieveValues. Is there any other way to achieve this easily? (I'm always wondering why std::map does not include a member function for us to do so.)

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• Strange calculation problem in C multiply by 1.2 fails

  - by DoomStone

  I have this c code, where i need to calculate a dobule from a long. double result; long t2_value; t2_value = 72; result = t2_value * 1.2; Now this code crashes at "result = t2_value * 1.2;" only with the error "Vector 0000000006". Here is the strange thing, if i replace result = t2_value * 1.2; with result = 72 * 1.2; evything works just as it should, i have tryed type casting t2_value as an double result = ((double)t2_value * 1.2); or making it an int istead of a long, but nothing helps.

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• Proper use of use of "cor" function in R

  - by order

  I am interested to know what a proper x (vector matrix or data frame) input looks like. I am currently using the function in two different sorts of matrices. However, I am not sure how R would interpret my data the way I intend. I will explain the types of matrix by example. Type 1 Gene1 Gene2 Gene3 sample1 sample2 Type 2 Sample1 Sample2 Sample3 gene 1 gene 2 gene 3 Are either of these formats valid x parameters? I input both of types of matrices and get some results, but without knowing whether or not this a proper use the function, these are just random numbers. Thank you for your time. I apologize that this isn't more interesting.

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• Constructor Definition

  - by mctl87

  Ok so i have a class Vector: #include <cstdlib> class Vec { private: size_t size; int * ptab; public: Vec(size_t n); ~Vec() {delete [] ptab;} size_t size() const {return size;} int & operator[](int n) {return ptab[n];} int operator[](int n) const {return ptab[n];} void operator=(Vec const& v); }; inline Vec::Vec(size_t n) : size(n), ptab(new int[n]) { } and the problem is that in one of my homework exercises i have to extend constructor def, so all elements will be initialized with zeros. I thought i know the basics but cant get through this dynamic array -.- ps. sry for gramma and other mistakes ;)

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