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  • Fastest way to write large STL vector to file using STL

    - by ljubak
    I have a large vector (10^9 elements) of chars, and I was wondering what is the fastest way to write such vector to a file. So far I've been using next code: vector<char> vs; // ... Fill vector with data ofstream outfile("nanocube.txt", ios::out | ios::binary); ostream_iterator<char> oi(outfile, '\0'); copy(vs.begin(), vs.end(), oi); For this code it takes approximately two minutes to write all data to file. The actual question is: "Can I make it faster using STL and how"?

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  • Using local classes with STL algorithms

    - by David Rodríguez - dribeas
    I have always wondered why you cannot use locally defined classes as predicates to STL algorithms. In the question: Approaching STL algorithms, lambda, local classes and other approaches, BubbaT mentions says that 'Since the C++ standard forbids local types to be used as arguments' Example code: int main() { int array[] = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 }; std::vector<int> v( array, array+10 ); struct pair : public std::unary_function<int,bool> { bool operator()( int x ) { return !( x % 2 ); } }; std::remove_if( v.begin(), v.end(), pair() ); // error } Does anyone know where in the standard is the restriction? What is the rationale for disallowing local types?

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  • STL vector reserve() and copy()

    - by natersoz
    Greetings, I am trying to perform a copy from one vector (vec1) to another vector (vec2) using the following 2 abbreviated lines of code (full test app follows): vec2.reserve( vec1.size() ); copy(vec1.begin(), vec1.end(), vec2.begin()); While the call to vec2 sets the capacity of vector vec2, the copying of data to vec2 seems to not fill in the values from vec1 to vec2. Replacing the copy() function with calls to push_back() works as expected. What am I missing here? Thanks for your help. vectest.cpp test program followed by resulting output follows. Compiler: gcc 3.4.4 on cygwin. Nat /** * vectest.cpp */ #include <iostream> #include <vector> using namespace std; int main() { vector<int> vec1; vector<int> vec2; vec1.push_back(1); vec1.push_back(2); vec1.push_back(3); vec1.push_back(4); vec1.push_back(5); vec1.push_back(6); vec1.push_back(7); vec2.reserve( vec1.size() ); copy(vec1.begin(), vec1.end(), vec2.begin()); cout << "vec1.size() = " << vec1.size() << endl; cout << "vec1.capacity() = " << vec1.capacity() << endl; cout << "vec1: "; for( vector<int>::const_iterator iter = vec1.begin(); iter < vec1.end(); ++iter ) { cout << *iter << " "; } cout << endl; cout << "vec2.size() = " << vec2.size() << endl; cout << "vec2.capacity() = " << vec2.capacity() << endl; cout << "vec2: "; for( vector<int>::const_iterator iter = vec2.begin(); iter < vec2.end(); ++iter ) { cout << *iter << endl; } cout << endl; } output: vec1.size() = 7 vec1.capacity() = 8 vec1: 1 2 3 4 5 6 7 vec2.size() = 0 vec2.capacity() = 7 vec2:

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  • The C++ Standard Template Library as a BDB Database (part 1)

    - by Gregory Burd
    If you've used C++ you undoubtedly have used the Standard Template Libraries. Designed for in-memory management of data and collections of data this is a core aspect of all C++ programs. Berkeley DB is a database library with a variety of APIs designed to ease development, one of those APIs extends and makes use of the STL for persistent, transactional data storage. dbstl is an STL standard compatible API for Berkeley DB. You can make use of Berkeley DB via this API as if you are using C++ STL classes, and still make full use of Berkeley DB features. Being an STL library backed by a database, there are some important and useful features that dbstl can provide, while the C++ STL library can't. The following are a few typical use cases to use the dbstl extensions to the C++ STL for data storage. When data exceeds available physical memory.Berkeley DB dbstl can vastly improve performance when managing a dataset which is larger than available memory. Performance suffers when the data can't reside in memory because the OS is forced to use virtual memory and swap pages of memory to disk. Switching to BDB's dbstl improves performance while allowing you to keep using STL containers. When you need concurrent access to C++ STL containers.Few existing C++ STL implementations support concurrent access (create/read/update/delete) within a container, at best you'll find support for accessing different containers of the same type concurrently. With the Berkeley DB dbstl implementation you can concurrently access your data from multiple threads or processes with confidence in the outcome. When your objects are your database.You want to have object persistence in your application, and store objects in a database, and use the objects across different runs of your application without having to translate them to/from SQL. The dbstl is capable of storing complicated objects, even those not located on a continous chunk of memory space, directly to disk without any unnecessary overhead. These are a few reasons why you should consider using Berkeley DB's C++ STL support for your embedded database application. In the next few blog posts I'll show you a few examples of this approach, it's easy to use and easy to learn.

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  • is c++ STL algorithms and containers same across platforms and performance?

    - by Abhilash M
    After learning good amount of c++, i'm now into STL containers and algorithms template library, my major concerns are, 1) Is this library same across different platforms like MS, linux n other os? 2) will quality or efficiency of program c++ module decrease with more use of STL containers and algorithms, i think i can't customize it to all needs. 3) Is this template library good to use in linux system programming, kernel modules? 4) lastly can i use this in programming contests, because it relives a lot of coding and pressure off shoulders.

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  • Using static vs. member find method on a STL set?

    - by B Johnson
    I am using a set because, i want to use the quick look up property of a sorted container such as a set. I am wondering if I have to use the find member method to get the benefit of a sorted container, or can I also use the static find method in the STL algorithms? My hunch is that using the static version will use a linear search instead of a binary search like I want.

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  • Difference among STLPort and SGI STL

    - by Yan Cheng CHEOK
    Recently, I was buzzed by the following problem STL std::string class causes crashes and memory corruption on multi-processor machines while using VC6. I plan to use an alternative STL libraries instead of the one provided by VC6. I came across 2 libraries : STLPort and SGI STL I was wondering what is the difference between the 2. Which one I should use? Which one able to guarantee thread safety? Thanks.

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  • What is so great about STL?

    - by Zygrob
    Hello StackOverflow. I am a Java developer trying to learn C++. I have many times read over the web (including StackOverflow) that STL is the best collections library that you can get in *any* language. (Sorry, I do not have any citations atm) However after studying some STL, I am really failing to see what makes STL so special. Would you please shed some light on what sets STL apart from the collection libraries of other languages and make it the _best_ collection library? Thanks in advance, Zygr??b.

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  • Why won't .attr('checked','checked') set?

    - by Jason
    I have the following snippet of code (I'm using jQuery 1.4.2): $.post('/Ads/GetAdStatsRow/', { 'ad_id': id }, function(result) { $('#edit_ads_form tbody').prepend(result); $(result).find('td.select-ad input').attr('checked','checked').click(); }); Assume that the post works correctly and returns a correct pre-built <tr> with some <td>s. Here's the weirdness: the $(result).find() line finds the correct input (which is a checkbox, as it's the only input in the cell) and runs the chained click() function correctly, but it REFUSES to set the box as checked, which I need to happen. Here's a crazy twist, too... when I get super specific and change the $(result).find() line to this (the id of the checkbox): $('#ad_' + id).click(); It checks the box, but doesn't run the click() function! If I set it to $('#ad_' + id).attr('checked','checked').click(); it runs the click function as though the box were checked, but the box remains unchecked, and if I do $('#ad_' + id).click().attr('checked','checked'); it does nothing at all. What in the world could be the matter with this? I'm running out of hair.... Thanks!

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  • Possible defect with jQuery ':checked' selector (finding checked checkbox when there are none)

    - by Mphammad Ashour
    Found a strange thing. The following code is supposed to set a default value for a UI element based on whether one of a group of checkboxes (all having attribute name="privacy") is checked (in say, a form postback). If there is no value in the HTML sent by the server (the form is not a postback), the default value should be firstMenuItemKey. Otherwise, it should be the one checked in the underlying HTML. However, while this works on the first call to the URL that includes the form, a refresh of the page will set the value of defaultPrivacyValue to one of the privacy checkboxes'. I've checked that the server isn't checking the checkbox before the script runs (it's not). I've also checked whether somewhere else in the script is checking the checkbox (it's not). var defaultPrivacyValue = firstMenuItemKey; $('input[name=privacy]:checked').each(function() { defaultPrivacyValue = $(this).next().find('.name').text(); }); selectMenuItem(defaultPrivacyValue); When I chaged the selector to 'input[name=privacy][checked=checked]' it worked as expected. Is this a defect in the jQuery implementation of DOM retrieval based on the ':checked' selector???? I'm using jQuery 1.4.2. Thanks for any help you can give.

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  • Javascript: Remove checked status from disabled input (already checked)

    - by BoDiE2003
    Im trying to make this function to check an element and if its checked, or not, add or remove respective className. Also, if the element is disabled but is checked, it should un-check it and remove the className('yes') function init() { $(document.body).select('input').each(function(element) { if (!element.checked) { element.up().removeClassName('yes'); } else { element.up().addClassName('yes'); } if (element.checked && element.disabled) { element.checked = false; element.up().removeClassName('yes') } }); } Right now, the last part, is not working, no effect

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  • Switch from Microsofts STL to STLport

    - by Laserallan
    Hi! I'm using quite much STL in performance critical C++ code under windows. One possible "cheap" way to get some extra performance would be to change to a faster STL library. According to this post STLport is faster and uses less memory, however it's a few years old. Has anyone made this change recently and what were your results?

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  • Can I disable min, max in STL?

    - by P-P
    Hi, I use one library which is very important and untouchable. The problem is that library declare min, max function, so when I include STL header in project, they conflict. I want to disable min, max function in STL (like #define NOMNMAX) if I could. If I can't, what would be solution? Thanks, in advance.

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  • Version of STL optimized for compile time?

    - by anon
    Hi! I'm looking for a variant of the STL (it's okay if it doesn't have all the functionality) that's optimized for short compile times -- I get bothered by long compile times that delay my compile-debug-edit cycle. I'm mainly interested in the containers of the STL: vector/map, and not so much the algorithms. Thanks!

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  • printing stl containers with gdb 7.0

    - by Andrei
    I have installed GDB 7.0 and python per the following instructions. In the same manual, there is a mention of this file stl-views-1.0.3.gdb. What confuses me, is where should it be placed in order to enable pretty printing of stl containers. Would someone also explain to me all of this work? Thanks

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  • stl priority queue based on lower value first

    - by russell
    I have a problem with stl priority queue.I want to have the priority queue in the increasing order,which is decreasing by default.Is there any way to do this in priority queue. And what is the complexity of building stl priority queue.If i use quick sort in an array which takes O(nlgn) is its complexity is similar to using priority queue??? Plz someone ans.Advanced thanx.

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  • why no += operator for vectors in stl

    - by Akshay Bhat
    I am curious? What high fundu logic goes behind not implementing: result+=vector1; where both result and vector1 are stl vectors. Note: i know how to implement that bit, but i need to know what logic, the sages who designed STL were using when they chose not to implement this feature?

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  • STL container to pop() by priority?

    - by Pirate for Profit
    I'm writing a thread-pool for Qt as QRunnable doesn't handle event loops in new threads. Not too familiar with STL, what would be the best way to pop() something by priority? Priority should probably be a property of MyRunnable imo, but I can always give that info to an STL container when adding the runnable to the queue.

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  • How much of STL is too much?

    - by Darius Kucinskas
    I am using a lot of STL code with std::for_each, bind, and so on, but I noticed that sometimes STL usage is not good idea. For example if you have a std::vector and want to do one action on each item of the vector, your first idea is to use this: std::for_each(vec.begin(), vec.end(), Foo()) and it is elegant and ok, for a while. But then comes the first set of bug reports and you have to modify code. Now you should add parameter to call Foo(), so now it becomes: std::for_each(vec.begin(), vec.end(), std::bind2nd(Foo(), X)) but that is only temporary solution. Now the project is maturing and you understand business logic much better and you want to add new modifications to code. It is at this point that you realize that you should use old good: for(std::vector::iterator it = vec.begin(); it != vec.end(); ++it) Is this happening only to me? Do you recognise this kind of pattern in your code? Have you experience similar anti-patterns using STL?

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