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  • Declaring STL Data Structures such as Vector in the .h

    - by sc_ray
    I am trying to declare a private Data Structure such as the Vector in my C++ header file which I want to eventually use within the method implementation of my .cpp. An example would be my header "SomeClass.h" where I have: class SomeClass { private: Vector<T> myVector; public: void AddTtoMyVector(T add); } And in my .cpp which is "SomeClass.cpp", I have the following: #include "SomeClass.h" SomeClass::AddTtoMyVector(T add) { myVector.Push_back(add); } Would the syntax here work? Or is there a different way of declaring and populating such structures?

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  • [C++][OpenMP] Proper use of "atomic directive" to lock STL container

    - by conradlee
    I have a large number of sets of integers, which I have, in turn, put into a vector of pointers. I need to be able to update these sets of integers in parallel without causing a race condition. More specifically. I am using OpenMP's "parallel for" construct. For dealing with shared resources, OpenMP offers a handy "atomic directive," which allows one to avoid a race condition on a specific piece of memory without using locks. It would be convenient if I could use the "atomic directive" to prevent simultaneous updating to my integer sets, however, I'm not sure whether this is possible. Basically, I want to know whether the following code could lead to a race condition vector< set<int>* > membershipDirectory(numSets, new set<int>); #pragma omp for schedule(guided,expandChunksize) for(int i=0; i<100; i++) { set<int>* sp = membershipDirectory[5]; #pragma omp atomic sp->insert(45); } (Apologies for any syntax errors in the code---I hope you get the point) I have seen a similar example of this for incrementing an integer, but I'm not sure whether it works when working with a pointer to a container as in my case.

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  • Performing time consuming operation on STL container within a lock

    - by Ashley
    I have an unordered_map of an unordered_map which stores a pointer of objects. The unordered map is being shared by multiple threads. I need to iterate through each object and perform some time consuming operation (like sending it through network etc) . How could I lock the multiple unordered_map so that it won't blocked for too long? typedef std::unordered_map<string, classA*>MAP1; typedef std::unordered_map<int, MAP1*>MAP2; MAP2 map2; pthread_mutex_lock(&mutexA) //how could I lock the maps? Could I reduce the lock granularity? for(MAP2::iterator it2 = map2.begin; it2 != map2.end; it2++) { for(MAP1::iterator it1 = *(it2->second).begin(); it1 != *(it2->second).end(); it1++) { //perform some time consuming operation on it1->second eg sendToNetwork(*(it1->second)); } } pthread_mutex_unlock(&mutexA)

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  • pointer delegate in STL set.

    - by ananth
    hi. Im kinda stuck with using a set with a pointer delegate. my code is as follows: void Graph::addNodes (NodeSet& nodes) { for (NodeSet::iterator pos = nodes.begin(); pos != nodes.end(); ++pos) { addNode(*pos); } } Here NodeSet is defined as: typedef std::set NodeSet; The above piece of code works perfectly on my windows machine, but when i run the same piece of code on a MAC, it gives me the following error: no matching function for call to 'Graph::addNode(const boost::shared_ptr&)' FYI, Node_ptr is of type: typedef boost::shared_ptr Node_ptr; can somebody plz tell me why this is happening?

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  • Does acos, atan functions in stl uses lots of cpu cycles

    - by jan
    Hi all, I wanted to calculate the angle between two vectors but I have seen these inverse trig operations such as acos and atan uses lots of cpu cycles. Is there a way where I can get this calculation done without using these functions? Also, does these really hit you when you in your optimization?

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  • Multithreading with STL container

    - by Steven
    I have an unordered map which stores a pointer of objects. I am not sure whether I am doing the correct thing to maintain the thread safety. typedef std::unordered_map<string, classA*>MAP1; MAP1 map1; pthread_mutex_lock(&mutexA) if(map1.find(id) != map1.end()) { pthread_mutex_unlock(&mutexA); //already exist, not adding items } else { classA* obj1 = new classA; map1[id] = obj1; obj1->obtainMutex(); //Should I create a mutex for each object so that I could obtain mutex when I am going to update fields for obj1? pthread_mutex_unlock(&mutexA); //release mutex for unordered_map so that other threads could access other object obj1->field1 = 1; performOperation(obj1); //takes some time obj1->releaseMutex(); //release mutex after updating obj1 }

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  • C++ STL: Trouble with iterators

    - by Rosarch
    I'm having a beginner problem: bool _isPalindrome(const string& str) { return _isPalindrome(str.begin(), str.end()); // won't compile } bool _isPalindrome(string::iterator begin, string::iterator end) { return begin == end || *begin == *end && _isPalindrome(++begin, --end); } What am I doing wrong here? Why doesn't str.begin() get type checked to be a string::iterator?

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  • A map and set which uses contiguous memory and has a reserve function

    - by edA-qa mort-ora-y
    I use several maps and sets. The lack of contiguous memory, and high number of (de)allocations, is a performance bottleneck. I need a mainly STL-compatbile map and set class which can use a contiguous block of memory for internal objects (or multiple blocks). It also needs to have a reserve function so that I can preallocate for expected sizes. Before I write my own I'd like to check what is available first. Is there something in Boost which does this? Does somebody know of an available implementation elsewhere? Intrusive collection types are not usable here as the same objects need to exist in several collections. As far as I know STL memory pools are per-type, not per instance. These global pools are not efficient with respect to memory locality in mutli-cpu/core processing. Object pools don't work as the types will be shared between instance but their pool should not. In many cases a hash map may be an option in some cases.

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  • Determining if an unordered vector<T> has all unique elements

    - by Hooked
    Profiling my cpu-bound code has suggested I that spend a long time checking to see if a container contains completely unique elements. Assuming that I have some large container of unsorted elements (with < and = defined), I have two ideas on how this might be done: The first using a set: template <class T> bool is_unique(vector<T> X) { set<T> Y(X.begin(), X.end()); return X.size() == Y.size(); } The second looping over the elements: template <class T> bool is_unique2(vector<T> X) { typename vector<T>::iterator i,j; for(i=X.begin();i!=X.end();++i) { for(j=i+1;j!=X.end();++j) { if(*i == *j) return 0; } } return 1; } I've tested them the best I can, and from what I can gather from reading the documentation about STL, the answer is (as usual), it depends. I think that in the first case, if all the elements are unique it is very quick, but if there is a large degeneracy the operation seems to take O(N^2) time. For the nested iterator approach the opposite seems to be true, it is lighting fast if X[0]==X[1] but takes (understandably) O(N^2) time if all the elements are unique. Is there a better way to do this, perhaps a STL algorithm built for this very purpose? If not, are there any suggestions eek out a bit more efficiency?

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  • Determing if an unordered vector<T> has all unique elements

    - by Hooked
    Profiling my cpu-bound code has suggested I that spend a long time checking to see if a container contains completely unique elements. Assuming that I have some large container of unsorted elements (with < and = defined), I have two ideas on how this might be done: The first using a set: template <class T> bool is_unique(vector<T> X) { set<T> Y(X.begin(), X.end()); return X.size() == Y.size(); } The second looping over the elements: template <class T> bool is_unique2(vector<T> X) { typename vector<T>::iterator i,j; for(i=X.begin();i!=X.end();++i) { for(j=i+1;j!=X.end();++j) { if(*i == *j) return 0; } } return 1; } I've tested them the best I can, and from what I can gather from reading the documentation about STL, the answer is (as usual), it depends. I think that in the first case, if all the elements are unique it is very quick, but if there is a large degeneracy the operation seems to take O(N^2) time. For the nested iterator approach the opposite seems to be true, it is lighting fast if X[0]==X[1] but takes (understandably) O(N^2) time if all the elements are unique. Is there a better way to do this, perhaps a STL algorithm built for this very purpose? If not, are there any suggestions eek out a bit more efficiency?

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  • LXC Container Networking

    - by digitaladdictions
    I just started to experiment with LXC containers. I was able to create a container and start it up but I cannot get dhcp to assign the container an IP address. If I assign a static address the container can ping the host IP but not outside the host IP. The host is CentOS 6.5 and the guest is Ubuntu 14.04LTS. I used the template downloaded by lxc-create -t download -n cn-01 command. If I am trying to get an IP address on the same subnet as the host I don't believe I should need the IP tables rule for masquerading but I added it anyways. Same with IP forwarding. I compiled LXC by hand from the following source https://linuxcontainers.org/downloads/lxc-1.0.4.tar.gz Host Operating System Version #> cat /etc/redhat-release CentOS release 6.5 (Final) #> uname -a Linux localhost.localdomain 2.6.32-431.20.3.el6.x86_64 #1 SMP Thu Jun 19 21:14:45 UTC 2014 x86_64 x86_64 x86_64 GNU/Linux Container Config #> cat /usr/local/var/lib/lxc/cn-01/config # Template used to create this container: /usr/local/share/lxc/templates/lxc-download # Parameters passed to the template: # For additional config options, please look at lxc.container.conf(5) # Distribution configuration lxc.include = /usr/local/share/lxc/config/ubuntu.common.conf lxc.arch = x86_64 # Container specific configuration lxc.rootfs = /usr/local/var/lib/lxc/cn-01/rootfs lxc.utsname = cn-01 # Network configuration lxc.network.type = veth lxc.network.flags = up lxc.network.link = br0 LXC default.confu 1500 qdisc pfifo_fast state UP qlen 1000 link/ether 00:0c:29:12:30:f2 brd ff:ff:ff:ff:f #> cat /usr/local/etc/lxc/default.conf lxc.network.type = veth lxc.network.link = br0 lxc.network.flags = up #> lxc-checkconfig Kernel configuration not found at /proc/config.gz; searching... Kernel configuration found at /boot/config-2.6.32-431.20.3.el6.x86_64 --- Namespaces --- Namespaces: enabled Utsname namespace: enabled Ipc namespace: enabled Pid namespace: enabled User namespace: enabled Network namespace: enabled Multiple /dev/pts instances: enabled --- Control groups --- Cgroup: enabled Cgroup namespace: enabled Cgroup device: enabled Cgroup sched: enabled Cgroup cpu account: enabled Cgroup memory controller: /usr/local/bin/lxc-checkconfig: line 103: [: too many arguments enabled Cgroup cpuset: enabled --- Misc --- Veth pair device: enabled Macvlan: enabled Vlan: enabled File capabilities: /usr/local/bin/lxc-checkconfig: line 118: [: -gt: unary operator expected Note : Before booting a new kernel, you can check its configuration usage : CONFIG=/path/to/config /usr/local/bin/lxc-checkconfig Network Config (HOST) #> cat /etc/sysconfig/network-scripts/ifcfg-br0 DEVICE=br0 TYPE=Bridge BOOTPROTO=dhcp ONBOOT=yes #> cat /etc/sysconfig/network-scripts/ifcfg-eth0 DEVICE=eth0 ONBOOT=yes TYPE=Ethernet IPV6INIT=no USERCTL=no BRIDGE=br0 #> cat /etc/networks default 0.0.0.0 loopback 127.0.0.0 link-local 169.254.0.0 #> ip a s 1: lo: <LOOPBACK,UP,LOWER_UP> mtu 16436 qdisc noqueue state UNKNOWN link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00 inet 127.0.0.1/8 scope host lo inet6 ::1/128 scope host valid_lft forever preferred_lft forever 2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP qlen 1000 link/ether 00:0c:29:12:30:f2 brd ff:ff:ff:ff:ff:ff inet6 fe80::20c:29ff:fe12:30f2/64 scope link valid_lft forever preferred_lft forever 3: pan0: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state DOWN link/ether 42:7e:43:b3:61:c5 brd ff:ff:ff:ff:ff:ff 4: br0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UNKNOWN link/ether 00:0c:29:12:30:f2 brd ff:ff:ff:ff:ff:ff inet 10.60.70.121/24 brd 10.60.70.255 scope global br0 inet6 fe80::20c:29ff:fe12:30f2/64 scope link valid_lft forever preferred_lft forever 12: vethT6BGL2: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP qlen 1000 link/ether fe:a1:69:af:50:17 brd ff:ff:ff:ff:ff:ff inet6 fe80::fca1:69ff:feaf:5017/64 scope link valid_lft forever preferred_lft forever #> brctl show bridge name bridge id STP enabled interfaces br0 8000.000c291230f2 no eth0 vethT6BGL2 pan0 8000.000000000000 no #> cat /proc/sys/net/ipv4/ip_forward 1 # Generated by iptables-save v1.4.7 on Fri Jul 11 15:11:36 2014 *nat :PREROUTING ACCEPT [34:6287] :POSTROUTING ACCEPT [0:0] :OUTPUT ACCEPT [0:0] -A POSTROUTING -o eth0 -j MASQUERADE COMMIT # Completed on Fri Jul 11 15:11:36 2014 Network Config (Container) #> cat /etc/network/interfaces # This file describes the network interfaces available on your system # and how to activate them. For more information, see interfaces(5). # The loopback network interface auto lo iface lo inet loopback auto eth0 iface eth0 inet dhcp #> ip a s 11: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP qlen 1000 link/ether 02:69:fb:42:ee:d7 brd ff:ff:ff:ff:ff:ff inet6 fe80::69:fbff:fe42:eed7/64 scope link valid_lft forever preferred_lft forever 13: lo: <LOOPBACK,UP,LOWER_UP> mtu 16436 qdisc noqueue state UNKNOWN link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00 inet 127.0.0.1/8 scope host lo inet6 ::1/128 scope host valid_lft forever preferred_lft forever

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  • C++: Appending a vector to a vector

    - by sub
    Assuming I have 2 STL vectors: vector<int> a; vector<int> b; Let's also say the both have around 30 elements. How do I add the vector b to the end of vector a? The dirty way would be iterating through b and adding each element via push_back, though I wouldn't like to do that!

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  • What C++ pitfalls should I avoid ?

    - by Craig H
    I remember first learning about vectors in the STL and after some time, I wanted to use a vector of bools for one of my projects. After seeing some strange behavior and doing some research, I learned that a vector of bools is not really a vector of bools. Anyone out there have any other common pitfalls to avoid in C++?

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  • Do I need to check capacity before adding an element to a vector in c++ ?

    - by Cassie
    Hi dear all, I am a newbie to c++ STL vectors so sorry for silly questions in advence. :) In my program, I have a vector which needs to store unknown number of elements. Do I have to check if the vector has achieved its max_size before adding an new element to it ? Will a c++ compiler throw an exception automatically when a program tries to add elements to a full vector ? Thank you very much, Cassie

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  • Array performance question

    - by Konrad
    I am very familiar with STL vector (and other container) performance guarantees, however I can't seem to find anything concrete about plain arrays. Are pointer arithmetic and [] methods constant or linear time?

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  • Function in c++ for finding if a word is prefix

    - by VaioIsBorn
    Let say i have some words AB, AAB, AA. AB is not a prefix to AAB but AA is a prefix to AAB because if i just add B at the end of AA it will become AAB, which is not possible with AB. So, is there any function in c++ (STL) so that i can determine of two words if one is prefix to the another ? Thanks.

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  • C++ dictionary/map with added order

    - by Gopalakrishnan Subramani
    I want to have something similar to map but while iterating I want them to be in the same order as it is added. Example map.insert("one", 1); map.insert("two", 2); map.insert("three", 3); While iterating I want the items to be like "one", ""two", "three"..By default, map doesn't provide this added order. How to get the map elements the way I have added? Anything with STL is fine or other alternative suggestions also fine

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