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  • Embarassing C++ question regarding const

    - by Neil Butterworth
    My comments on this answer got me thinking about the issues of constness and sorting. I played around a bit and reduced my issues to the fact that this code: #include <vector> int main() { std::vector <const int> v; } will not compile - you can't create a vector of const ints. I suppose I should have known this, but I've never needed to create such a thing before. However, it seems like a useful construct to me, and I wonder if there is any way round this problem - I want to add things to a vector (or whatever), but they should not be changed once added. There's probably some embarrassingly simple solution to this, but it's something I'd never considered before.

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  • allocating extra memory for a container class.

    - by sil3nt
    Hey there, I'm writing a template container class and for the past few hours have been trying to allocate new memory for extra data that comes into the container (...hit a brick wall..:| ) template <typename T> void Container<T>::insert(T item, int index){ if ( index < 0){ cout<<"Invalid location to insert " << index << endl; return; } if (index < sizeC){ //copying original array so that when an item is //placed in the middleeverything else is shifted forward T *arryCpy = 0; int tmpSize = 0; tmpSize = size(); arryCpy = new T[tmpSize]; int i = 0, j = 0; for ( i = 0; i < tmpSize; i++){ for ( j = index; j < tmpSize; j++){ arryCpy[i] = elements[j]; } } //overwriting and placing item and location index elements[index] = item; //copying back everything else after the location at index int k = 0, l = 0; for ( k =(index+1), l=0; k < sizeC || l < (sizeC-index); k++,l++){ elements[k] = arryCpy[l]; } delete[] arryCpy; arryCpy = 0; } //seeing if the location is more than the current capacity //and hence allocating more memory if (index+1 > capacityC){ int new_capacity = 0; int current_size = size(); new_capacity = ((index+1)-capacityC)+capacityC; //variable for new capacity T *tmparry2 = 0; tmparry2 = new T[new_capacity]; int n = 0; for (n = 0; n < current_size;n++){ tmparry2[n] = elements[n]; } delete[] elements; elements = 0; //copying back what we had before elements = new T[new_capacity]; int m = 0; for (m = 0; m < current_size; m++){ elements[m] = tmparry2[m]; } //placing item elements[index] = item; } else{ elements[index] = item; } //increasing the current count sizeC++; my testing condition is Container cnt4(3); and as soon as i hit the fourth element (when I use for egsomething.insert("random",3);) it crashes and the above doesnt work. where have I gone wrong?

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  • Access Voilation in std::pair

    - by sameer karjatkar
    I have an application which is trying to populate a pair . Out of no where the application crashes . The Windbg analysis on the crash dump suggest PRIMARY_PROBLEM_CLASS: INVALID_POINTER_READ DEFAULT_BUCKET_ID: INVALID_POINTER_READ STACK_TEXT: 0389f1dc EPFilter32!std::vector,std::allocator ::size+0xc INVALID_POINTER_READ_c0000005_Test.DLL!std::vector_std::pair_unsigned_int, unsigned_int_,std::allocator_std::pair_unsigned_int,unsigned_int___::size Following is the statement in the code where it fails const branch_info& b1 = en1.m_branches[i1]; where branch_info is std::pair and the en1.m_branches[i1] fetches me a pair value

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  • Deleting a element from a vector of pointers in C++.

    - by Kranar
    I remember hearing that the following code is not C++ compliant and was hoping someone with much more C++ legalese than me would be able to confirm or deny it. std::vector<int*> intList; intList.push_back(new int(2)); intList.push_back(new int(10)); intList.push_back(new int(17)); for(std::vector<int*>::iterator i = intList.begin(); i != intList.end(); ++i) { delete *i; } intList.clear() The rationale was that it is illegal for a vector to contain pointers to invalid memory. Now obviously my example will compile and it will even work on all compilers I know of, but is it standard compliant C++ or am I supposed to do the following, which I was told is in fact the standard compliant approach: while(!intList.empty()) { int* element = intList.back(); intList.pop_back(); delete element; }

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  • how to specify a pointer to an overloaded function?

    - by davka
    I want to pass an overloaded function to the std::for_each() algorithm. e.g.: void f(char c); void f(int i); std::string s("example"); std::for_each(s.begin(), s.end(), f); I'd expect the compiler to resolve f() by the iterator type. Apparently, it (gcc 4.1.2) doesn't do it. So, how can I specify which f() I want? thanks a lot

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  • sort std::list case sensitive elements

    - by Dave18
    #include <list> #include <string> using std::string; using std::list; int main() { list <string> list_; list_.push_back("C"); list_.push_back("a"); list_.push_back("b"); list_.sort(); } does sort() function sort the elements according to their character codes? I want the result here to be a b C after the sorting is done.

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  • Iterator to last element in std::list

    - by Dave18
    #include <list> using std::list; int main() { list <int> n; n.push_back(1); n.push_back(2); n.push_back(3); list <int>::iterator iter = n.begin(); std::advance(iter, n.size() - 1); //iter is set to last element } is there any other way to have an iter to the last element in list?

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  • Is there a sorted_vector class, which supports insert() etc.?

    - by Frank
    Often, it is more efficient to use a sorted std::vector instead of a std::set. Does anyone know a library class sorted_vector, which basically has a similar interface to std::set, but inserts elements into the sorted vector (so that there are no duplicates), uses binary search to find elements, etc.? I know it's not hard to write, but probably better not to waste time and use an existing implementation anyway.

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  • Get last/newly added element in std::set

    - by Dave17
    can you get the last or newly added element in std::set? for example say if the loop runs to collect the elements to fill in the std::set. if on the first run the set was, [0] "A" [1] "B" [2] "D" and, on second run, the set becomes [0] "A" [1] "B" [2] "C" [3] "D" How would you check if 'C' is the new element that was added?

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  • Why does string::find return size_type and not an iterator?

    - by dehmann
    In C++, why does string::find return size_type and not an iterator? It would make sense because functions like string::replace or string::insert take iterators as input, so you could find some character and immediately pass the returned iterator to replace, etc. Also, std::find returns an iterator -- why is std::string::find different?

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  • How to initialize std::vector from C-style array?

    - by dehmann
    What is the cheapest way to initialize a std::vector from a C-style array? Example: In the following class, I have a vector, but due to outside restrictions, the data will be passed in as C-style array: class Foo { std::vector<double> w_; public: void set_data(double* w, int len){ // how to cheaply initialize the std::vector? } Obviously, I can call w_.resize() and then loop over the elements, or call std::copy(). Are there any better methods?

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  • Best way to handle storing (possibly NULL) char * in a std::string

    - by John
    class MyClass { public: void setVar(const char *str); private: std::string mStr; int maxLength; //we only store string up to this length }; What's the best approach to implement setVar when the external code is quite likely to pass in NULL for an empty string (and cannot be changed)? I currently do something a bit like: void MyClass::setVar(const char *str) { mStr.assign(str ? str : "",maxLength); } But it seems kind of messy. ideas?

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  • how-to initialize 'const std::vector<T>' like a c array

    - by vscharf
    Is there an elegant way to create and initialize a const std::vector<const T> like const T a[] = { ... } to a fixed (and small) number of values? I need to call a function frequently which expects a vector<T>, but these values will never change in my case. In principle I thought of something like namespace { const std::vector<const T> v(??); } since v won't be used outside of this compilation unit.

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  • including a std::map within a struct? Is it ok?

    - by user553514
    class X_class{ public: struct extra {int extra1; int extra2; int extra3; }; enum a { n,m}; struct x_struct{ char b; char c; int d; int e; std::map <int, extra> myExtraMap; }; }; in my code I define : x_struct myStruct; why do I get compile errors compiling the above class? The error either says: 1) expected ; before < on the line --- where I defined the map (above) if I eliminate std:: or 2) error: invalid use of ::; error: expected ; before < token

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  • Performance of vector::size() : is it as fast as reading a variable?

    - by zoli2k
    I have do an extensive calculation on a big vector of integers. The vector size is not changed during the calculation. The size of the vector is frequently accessed by the code. What is faster in general: using the vector::size() function or using helper constant vectorSize storing the size of the vector? I know that compilers usually able to inline the size() function when setting the proper compiler flags, however, making a function inline is something that a compiler may do but can not be forced.

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  • Can set_intersection be used with hash_set in C++?

    - by R S
    I am calculating intersection, union and differences of sets. I have a typedef of my set type: typedef set<node_type> node_set; When it is replaced with typedef hash_set<node_type> node_set; The results are different. It's a complicated program, and before I start debugging - am I doing it right? When I use functions like this: set_intersection(v_higher.begin(), v_higher.end(), neighbors[w].begin(), neighbors[w].end(), insert_iterator<node_set>(tmp1, tmp1.begin())); should they work seamlessly with both set and hash_set?

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  • Cant finish upgrade from 11.10 to 12 on VPS based on Parallels Virtuozzo Containers, due to libc6

    - by Carmageddon
    I was stuck with this problem near the end of an upgrade: WARNING: this version of the GNU libc requires kernel version 2.6.24 or later. Please upgrade your kernel before installing glibc. The installation of a 2.6 kernel could ask you to install a new libc first, this is NOT a bug, and should NOT be reported. In that case, please add lenny sources to your /etc/apt/sources.list and run: apt-get install -t lenny linux-image-2.6 Their suggested stepds dont work on VPS, and after googling, I came up to this: Why did my upgrade to 12.04 fail with "glibc not found" or "libc6" or "requires kernel 2.6.24" error? There is comment by izx which explains my problem and proposes a workaround (might take a while to convince the guys to upgrade the kernel..). However, when I follow his instructions, I get error: # apt-get -f install Reading package lists... Done Building dependency tree Reading state information... Done Correcting dependencies... Done The following extra packages will be installed: libc-dev-bin libc6 libc6-dev libnih1 Suggested packages: glibc-doc The following packages will be upgraded: libc-dev-bin libc6 libc6-dev libnih1 4 upgraded, 0 newly installed, 0 to remove and 394 not upgraded. 1 not fully installed or removed. Need to get 0 B/7737 kB of archives. After this operation, 233 kB disk space will be freed. Do you want to continue [Y/n]? y locale: /lib/x86_64-linux-gnu/libc.so.6: version `GLIBC_2.15' not found (required by locale) locale: /lib/x86_64-linux-gnu/libc.so.6: version `GLIBC_2.14' not found (required by locale) Preconfiguring packages ... (Reading database ... 35175 files and directories currently installed.) Preparing to replace libc6-dev 2.13-20ubuntu5.2 (using .../libc6-dev_2.15-0ubuntu10.3_amd64.deb) ... Unpacking replacement libc6-dev ... Preparing to replace libc-dev-bin 2.13-20ubuntu5.2 (using .../libc-dev-bin_2.15-0ubuntu10.3_amd64.deb) ... Unpacking replacement libc-dev-bin ... Preparing to replace libc6 2.13-20ubuntu5.2 (using .../libc6_2.15-0ubuntu10.3_amd64.deb) ... locale: /lib/x86_64-linux-gnu/libc.so.6: version `GLIBC_2.15' not found (required by locale) locale: /lib/x86_64-linux-gnu/libc.so.6: version `GLIBC_2.14' not found (required by locale) Checking for services that may need to be restarted... Checking init scripts... runlevel:/var/run/utmp: No such file or directory Checking for services that may need to be restarted... Checking init scripts... runlevel:/var/run/utmp: No such file or directory WARNING: init script for samba not found. Stopping some services possibly affected by the upgrade (will be restarted later): cron: stopping...done. WARNING: this version of the GNU libc requires kernel version 2.6.24 or later. Please upgrade your kernel before installing glibc. The installation of a 2.6 kernel _could_ ask you to install a new libc first, this is NOT a bug, and should *NOT* be reported. In that case, please add lenny sources to your /etc/apt/sources.list and run: apt-get install -t lenny linux-image-2.6 Then reboot into this new kernel, and proceed with your upgrade dpkg: error processing /var/cache/apt/archives/libc6_2.15-0ubuntu10.3_amd64.deb (--unpack): subprocess new pre-installation script returned error exit status 1 Processing triggers for man-db ... locale: /lib/x86_64-linux-gnu/libc.so.6: version `GLIBC_2.15' not found (required by locale) locale: /lib/x86_64-linux-gnu/libc.so.6: version `GLIBC_2.14' not found (required by locale) Errors were encountered while processing: /var/cache/apt/archives/libc6_2.15-0ubuntu10.3_amd64.deb E: Sub-process /usr/bin/dpkg returned an error code (1) I also attempted to manually grab the .deb package and install it using dpkg -i, but getting: locale: /lib/x86_64-linux-gnu/libc.so.6: version `GLIBC_2.15' not found (required by locale) Even though the file is: libc-bin_2.15-0ubuntu10+openvz0_amd64.deb

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