Search Results

Search found 1933 results on 78 pages for 'boost tuples'.

Page 34/78 | < Previous Page | 30 31 32 33 34 35 36 37 38 39 40 41  | Next Page >

• c++ class member functions selected by traits

  - by Jive Dadson

  I am reluctant to say I can't figure this out, but I can't figure this out. I've googled and searched stackoverflow, and come up empty. The abstract, and possibly overly vague form of the question is, how can I use the traits-pattern to instantiate non-virtual member functions? The question came up while modernizing a set of multivariate function optimizers that I wrote more than 10 years ago. The optimizers all operate by selecting a straight-line path through the parameter space away from the current best point (the "update"), then finding a better point on that line (the "line search"), then testing for the "done" condition, and if not done, iterating. There are different methods for doing the update, the line-search, and conceivably for the done test, and other things. Mix and match. Different update formulae require different state-variable data. For example, the LMQN update requires a vector, and the BFGS update requires a matrix. If evaluating gradients is cheap, the line-search should do so. If not, it should use function evaluations only. Some methods require more accurate line-searches than others. Those are just some examples. The original version instatiates several of the combinations by means of virtual functions. Some traits are selected by setting mode bits. Yuck. It would be trivial to define the traits with #define's and the member functions with #ifdef's and macros. But that's so twenty years ago. It bugs me that I cannot figure out a whiz-bang modern way. If there were only one trait that varied, I could use the curiously recurring template pattern. But I see no way to extend that to arbitrary combinations of traits. I tried doing it using boost::enable_if, etc.. The specialized state info was easy. I managed to get the functions done, but only by resorting to non-friend external functions that have the this-pointer as a parameter. I never even figured out how to make the functions friends, much less member functions. Perhaps tag-dispatch is the key. I haven't gotten very deeply into that. Surely it's possible, right? If so, what is best practice?

  Read the article

• c++ class member functions instatiated by traits

  - by Jive Dadson

  I am reluctant to say I can't figure this out, but I can't figure this out. I've googled and searched stackoverflow, and come up empty. The abstract, and possibly overly vague form of the question is, how can I use the traits-pattern to instantiate non-virtual member functions? The question came up while modernizing a set of multivariate function optimizers that I wrote more than 10 years ago. The optimizers all operate by selecting a straight-line path through the parameter space away from the current best point (the "update"), then finding a better point on that line (the "line search"), then testing for the "done" condition, and if not done, iterating. There are different methods for doing the update, the line-search, and conceivably for the done test, and other things. Mix and match. Different update formulae require different state-variable data. For example, the LMQN update requires a vector, and the BFGS update requires a matrix. If evaluating gradients is cheap, the line-search should do so. If not, it should use function evaluations only. Some methods require more accurate line-searches than others. Those are just some examples. The original version instantiates several of the combinations by means of virtual functions. Some traits are selected by setting mode bits that are tested at runtime. Yuck. It would be trivial to define the traits with #define's and the member functions with #ifdef's and macros. But that's so twenty years ago. It bugs me that I cannot figure out a whiz-bang modern way. If there were only one trait that varied, I could use the curiously recurring template pattern. But I see no way to extend that to arbitrary combinations of traits. I tried doing it using boost::enable_if, etc.. The specialized state info was easy. I managed to get the functions done, but only by resorting to non-friend external functions that have the this-pointer as a parameter. I never even figured out how to make the functions friends, much less member functions. The compiler (vc++ 2008) always complained that things didn't match. I would yell, "SFINAE, you moron!" but the moron is probably me. Perhaps tag-dispatch is the key. I haven't gotten very deeply into that. Surely it's possible, right? If so, what is best practice?

  Read the article

• C++ class member functions instantiated by traits

  - by Jive Dadson

  I am reluctant to say I can't figure this out, but I can't figure this out. I've googled and searched Stack Overflow, and come up empty. The abstract, and possibly overly vague form of the question is, how can I use the traits-pattern to instantiate non-virtual member functions? The question came up while modernizing a set of multivariate function optimizers that I wrote more than 10 years ago. The optimizers all operate by selecting a straight-line path through the parameter space away from the current best point (the "update"), then finding a better point on that line (the "line search"), then testing for the "done" condition, and if not done, iterating. There are different methods for doing the update, the line-search, and conceivably for the done test, and other things. Mix and match. Different update formulae require different state-variable data. For example, the LMQN update requires a vector, and the BFGS update requires a matrix. If evaluating gradients is cheap, the line-search should do so. If not, it should use function evaluations only. Some methods require more accurate line-searches than others. Those are just some examples. The original version instantiates several of the combinations by means of virtual functions. Some traits are selected by setting mode bits that are tested at runtime. Yuck. It would be trivial to define the traits with #define's and the member functions with #ifdef's and macros. But that's so twenty years ago. It bugs me that I cannot figure out a whiz-bang modern way. If there were only one trait that varied, I could use the curiously recurring template pattern. But I see no way to extend that to arbitrary combinations of traits. I tried doing it using boost::enable_if, etc.. The specialized state information was easy. I managed to get the functions done, but only by resorting to non-friend external functions that have the this-pointer as a parameter. I never even figured out how to make the functions friends, much less member functions. The compiler (VC++ 2008) always complained that things didn't match. I would yell, "SFINAE, you moron!" but the moron is probably me. Perhaps tag-dispatch is the key. I haven't gotten very deeply into that. Surely it's possible, right? If so, what is best practice?

  Read the article

• Generic Method to find the tuples used for computation in Postgres?

  - by Rahul

  If I have a table col1 | name | pay ------+------------------+------ 1 | Steve Jobs | 1006 2 | Mike Markkula | 1007 3 | Mike Scott | 1978 4 | John Sculley | 1983 5 | Michael Spindler | 1653 The user executes a sum query which sums the pay of people getting paid more than $1500. Is there a way to also implicitly know which tuples have been used which satisfy the condition for sum ? I know you can separately write another query to just return the primary key ids which satisfy the condition. But, Is there any other way to do that in the same query ? probably rewrite the query in some way ? or... any suggestion ?

  Read the article

• How can I reshape and aggregate list of tuples in Python?

  - by radek

  I'm a newb to Python so apologies in advance if my question looks trivial. From a psycopg2 query i have a result in the form of a list of tuples looking like: [(1, 0), (1, 0), (1, 1), (2, 1), (2, 2), (2, 2), (2, 2)] Each tuple represents id of a location where event happened and hour of the day when event took place. I'd like to reshape and aggregate this list with subtotals for each hour in each location, to a form where it looks like: [(1, 0, 2), (1, 1, 1), (1, 2, 0), (2, 0, 0), (2, 1, 1), (2, 3, 3)] Where each touple will now tell me that, for example: in location 1, at hour 0 there were 2 events; in location 1, at hour 1 there was 1 event; and so on... If there were 0 events at certain hour, I still would like to see it, as for example 0 events at 0 hours in location 2: (2, 0, 0) How could I implement it in Python?

  Read the article

• How to boost playback volume in real time on media recorded with a very low volume.

  - by L Marksman

  I have never heard a satisfactory answer to this often misunderstood question, let me explain. Lets say I have a sound card and earphones/speakers that can play back audio loud enough in most cases. This is great but the problem is that you always find people who do not know how to record audio, from Youtube video's to music. So now you end up with a audio playback that only uses 10% or less of the capacity of your sound hardware, in vista/win 7 you will see this frequently in the mixer with the volume pushed up to max but the green sound level only goes up a millimeter or two. I am looking for (preferably free) software or a method to boost the sound level of any audio from any source in real time to use more of my hardware capacity similar to what VLC media player can do. Oh and please, do not tell me it is impossible. I am not trying to boost the volume past what my hardware is capable of, I am just trying to use my hardware's full capacity. Also please do not tell met to buy new hardware, I know I can use hardware amplification, I don't want to (like many others) spend money on a simple little problem like this. Thanks!

  Read the article

• How to Use XSLT to Replace Coordinate Separator With List of Tuples?

  - by kuloch

  I have a space-separated list of coordinate tuples. Each tuple consists of a space-separated list of 2-dimensional coordinates. E.g. "1.1 2.8 1.2 2.9" represents a line from POINT(1.1 2.8) to POINT(1.2 2.9). I need this to instead be "1.1,2.8 1.2,2.9". How would I use XSLT to perform the replacement of space-to-comma between pairs of numbers? I have the "string(gml:LinearRing/gml:posList)". This is being used on a Java Web Service that spits out GML 3.1.1 features with geometries. The service supports optional KML output, by using XSLT to transform the GML document into a KML document (at least, the chunks deemed "important"). I am locked into XSLT 1.0, so regex from XSLT 2.0 is not an option. I am aware that GML uses lat/lon while KML uses lon/lat. That's being handled before XSLT, though it would be nice to have that also done with XSLT.

  Read the article

• Specify an inline callback function as an argument.

  - by Matthias Vance

  LS, Let me first explain what I'm trying to achieve using some pseudo-code (JavaScript). // Declare our function that takes a callback as as an argument, and calls the callback with true. B(func) { func(true); } // Call the function B(function(bool success) { /* code that uses success */ }); I hope this says it all. If not, please comment on my question so I can write a little more to clarify my issue. What I want is to have code like this in C++. I have tried to use lambda functions, but I was unable to specify a parameter type for those. Kind regards, Matthias Vance

  Read the article

• Adding python script to c++ project

  - by jon

  How would I go about adding a script written in python to a c++ project? Thanks

  Read the article

• Serialization with Qt

  - by Narek

  I am programming a GUI with Qt. In my GUI I have a huge std::map. And "MyType" is a class that has different kinds of filds. So, in a word, I want to serialize the std::map. How can I do that? Does Qt provides us with neccesary features? P.S. I would like to use std::map, NOT QMap.

  Read the article

• bitset to dynamic bitset

  - by mr.bio

  Hi.. I have a function where i use bitset.Now i need to convert it to a dynamic bitset.. but i don't know how. Can somebody help me ? set<string> generateCandidates(set<string> ck,unsigned int k){ set<string> nk ; for (set<string>::const_iterator p = ck.begin( );p != ck.end( ); ++p){ for (set<string>::const_iterator q = ck.begin( );q != ck.end( ); ++q){ bitset<4> bs1(*p); bitset<4> bs2(*q); bs1|= bs2 ; if(bs1.count() == k){ nk.insert(bs1.to_string<char,char_traits<char>,allocator<char> >()); } } } return nk; }

  Read the article

• What's the future of std::valarray look like?

  - by andand

  Up until fairly recently I hadn't been keeping up with the C++0x deliberations. As I try to become more familiar with it the issues being worked, I've come across sites like this which seems to be advocating for deprecating or removing std::valarray since most people are using Blitz++ in any event. I guess I'm probably one of the few people out there who uses std::valarray (and yes I know the class has a sordid past, a tarnished present, and a questionable future). For me they work, and perhaps more important, they're part of the standard (for now any way). Aside from the one site above, I've been able to find very little on what is actually happening with std::valarray in the new standard, and was hoping that somebody on SO might be able to provide some insight and / or references where Google, Wikipedia and even the C++ Standards Committee Web Site have so far failed me. Thanks.

  Read the article

• C++ auto function return type implementation [trailing-return-type]

  - by aaa

  hello. Is there macro, something like BOOST_AUTO, which would allow to emulate automatic return type deduction of function in C++? I mean something like trailing-return-type, http://en.wikipedia.org/wiki/C%2B%2B0x#Alternative_function_syntax thank you

  Read the article

• C++ imitating ls like commands

  - by Arman

  Hi, How to implement the ls "filename_[0-5][3-4]?" like class? The result I would like to store in the vector. Currently I am using system() which is calling ls, but this is not portable under MS. thanks, Arman.

  Read the article

• Wrapping allocated output parameters with a scoped_ptr/array

  - by Danra

  So, I have some code which looks like this: byte* ar; foo(ar) // Allocates a new[] byte array for ar ... delete[] ar; To make this safer, I used a scoped_array: byte* arRaw; scoped_array ar; foo(arRaw); ar.reset(arRaw); ... // No delete[] The question is, Is there any existing way to do this using just the scoped_array, without using a temporary raw array? I can probably write an in-place "resetter" class, just wondering if the functionality exists and I'm missing it. Thanks, Dan

  Read the article

• traversing a directory

  - by jc

  Is there any way to traverse the content of a directory? I would like to store the names of each folder in a given directory. Thanks!

  Read the article

• Regular expression quantifier questions

  - by Josemalive

  Hello, Im trying to find a regular expression that matches this kind of URL: http://sub.domain.com/selector/F/13/K/100546/sampletext/654654/K/sampletext_sampletext.html and dont match this: http://sub.domain.com/selector/F/13/K/10546/sampletext/5987/K/sample/K/101/sample_text.html only if the number of /K/ is minimum 1 and maximum 2 (something with a quantifier like {1,2}) Until this moment i have the following regexp: http://sub\.domain\.com/selector/F/[0-9]{1,2}/[a-z0-9_-]+/ Now i would need a hand to add any kind of condition like: Match this if in the text appears the /K/ from 1 to 2 times at most. Thanks in advance. Best Regards. Josema

  Read the article

• Difference between BOOST_CHECK_CLOSE and BOOST_CHECK_CLOSE_FRACTION?

  - by Rhys Ulerich

  Can anyone describe the difference in behavior between BOOST_CHECK_CLOSE and BOOST_CHECK_CLOSE_FRACTION? The documentation implies the that both macros treat their third parameter identically, which makes me suspect the documentation is wrong. In particular, BOOST_CHECK_CLOSE_FRACTION gives me some odd looking results: error in "...": difference between *expected{0} and *actual{-1.7763568394002506e-16} exceeds 9.9999999999999995e-07 Is there a gotcha because I expect a zero result? I've not been successful at reading through the underlying macro declarations. Please note BOOST_CHECK_SMALL isn't appropriate for my use case (comparing two vectors after a linear algebra operation).

  Read the article

• When should I use temporary variables?

  - by Kyle

  Specifically, I'm wondering which of these I should write: shared_ptr<GuiContextMenu> subMenu = items[j].subMenu.lock(); if (subMenu) subMenu->setVisible(false); or: if (items[j].subMenu.lock() items[j].subMenu.lock()->setVisible(false); I am not required to follow any style guidelines. After optimization, I don't think either choice makes a difference in performance. What is generally the preferred style and why?

  Read the article

• Some clarification needed about synchronous versus asynchronous asio operations

  - by Old newbie

  As far as I know, the main difference between synchronous and asynchronous operations. I.e. write() or read() vs async_write() and async_read() is that the former, don't return until the operation finish -or error-, and the last ones, returns inmediately. Due the fact that the asynchronous operations are controlled by an io_service.run() that does not finish until the controlled operations has finalized. It seems to me that in sequencial operations as those involved in TCP/IP connections with protocols such as POP3, in which the operaton is a sequence such as: C: <connect> S: Ok. C: User... S: Ok. C: Password S: Ok. C: Command S: answer C: Command S: answer ... C: bye S: <close> The difference between synchronous/asynchronous opperatons does not make much sense. Of course, in both operations there is allways the risk that the program flow stops indefinitely by some circunstance -there the use of timers-, but I would like know some more authorized opinions in this matter. I must admit that the question is rather ill-defined, but I like hear some advices about when use one or other, because I've problems in debugging with MS Visual Studio, asynchronous SSL operations in a POP3 client in wich I'm working now -about some of who surely I would write here soon-, and sometimes think that perhaps is a bad idea use asynchronous in this. Not to say that I'm an absolute newbie with this librarys, that additionally to the difficult with the idioma, and some obscure concepts in the STL, must suffer the brevity of the asio documentation.

  Read the article

• Unit Testing Private Method in Resource Managing Class (C++)

  - by BillyONeal

  I previously asked this question under another name but deleted it because I didn't explain it very well. Let's say I have a class which manages a file. Let's say that this class treats the file as having a specific file format, and contains methods to perform operations on this file: class Foo { std::wstring fileName_; public: Foo(const std::wstring& fileName) : fileName_(fileName) { //Construct a Foo here. }; int getChecksum() { //Open the file and read some part of it //Long method to figure out what checksum it is. //Return the checksum. } }; Let's say I'd like to be able to unit test the part of this class that calculates the checksum. Unit testing the parts of the class that load in the file and such is impractical, because to test every part of the getChecksum() method I might need to construct 40 or 50 files! Now lets say I'd like to reuse the checksum method elsewhere in the class. I extract the method so that it now looks like this: class Foo { std::wstring fileName_; static int calculateChecksum(const std::vector<unsigned char> &fileBytes) { //Long method to figure out what checksum it is. } public: Foo(const std::wstring& fileName) : fileName_(fileName) { //Construct a Foo here. }; int getChecksum() { //Open the file and read some part of it return calculateChecksum( something ); } void modifyThisFileSomehow() { //Perform modification int newChecksum = calculateChecksum( something ); //Apply the newChecksum to the file } }; Now I'd like to unit test the calculateChecksum() method because it's easy to test and complicated, and I don't care about unit testing getChecksum() because it's simple and very difficult to test. But I can't test calculateChecksum() directly because it is private. Does anyone know of a solution to this problem?

  Read the article

• why is unbounded_array more efficient than vector?

  - by Neil G

  It says here that The unbounded array is similar to a std::vector in that in can grow in size beyond any fixed bound. However unbounded_array is aimed at optimal performance. Therefore unbounded_array does not model a Sequence like std::vector does. What does this mean?

  Read the article

• Is it possible to generate a .h macros file from bjam?

  - by Gnurou

  I need to dynamically generate some macros into a .h configuration file that C programs can include in order to check which options are enabled, in a fashion similar to what is possible with CMake's CONFIGURE_FILE macro. But after looking in the doc and the web, I could not find something useful. Is it possible to generate such a file from bjam and have the dependencies handled correctly? If so, how would you do it?

  Read the article

• recursive_directory_iterator exception

  - by Jon

  I'm writing a simple program which moves files on my desktop to new location. I don't understand why it crashes after the file has been moved. for(recursive_directory_iterator it(desktop), end; it != end; ++it) { if(it->path().leaf() == fileToMove) { rename(*it, newPath); } } A point in the right direction would be appropriated. Thanks!

  Read the article

• What's the performance penalty of weak_ptr?

  - by Kornel Kisielewicz

  I'm currently designing a object structure for a game, and the most natural organization in my case became a tree. Being a great fan of smart pointers I use shared_ptr's exclusively. However, in this case, the children in the tree will need access to it's parent (example -- beings on map need to be able to access map data -- ergo the data of their parents. The direction of owning is of course that a map owns it's beings, so holds shared pointers to them. To access the map data from within a being we however need a pointer to the parent -- the smart pointer way is to use a reference, ergo a weak_ptr. However, I once read that locking a weak_ptr is a expensive operation -- maybe that's not true anymore -- but considering that the weak_ptr will be locked very often, I'm concerned that this design is doomed with poor performance. Hence the question: What is the performance penalty of locking a weak_ptr? How significant is it?

  Read the article

< Previous Page | 30 31 32 33 34 35 36 37 38 39 40 41  | Next Page >