CArray help
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From: Joseph M. Newcomer on 7 May 2010 14:17 I agree; I have largely replaced my use of CArray with std::vector. Note that the declartion is not CArray(type) but CArray<type>, Reading afxtempl.h is about the worst possible way to learn about this, because templates are not trivial aspects of C++ to work with. What do you WANT to do with it? The most relevant operations are SetSize GetSize Add GetAt SetAt SetAtGrow [] joe **** On Fri, 7 May 2010 16:37:14 +0200, "Giovanni Dicanio" <giovanniDOTdicanio(a)REMOVEMEgmail.com> wrote: >"RB" <NoMail(a)NoSpam> wrote: > >> Hello, I am struggling to learn the concept of template language >> and the usage of CArray. I have found the CArray declaration in >> the afxtempl.h file and I have managed to compile with no errors >> the apparent construction of > >May I suggest you to just go with STL std::vector? >It is more powerful than CArray. >For example, CArray does copies in a "naive" way using memcpy. This works >correctly only for PODs (Plain Ol' Data) but not for more complex classes. >Strange bugs may arise if you use CArray with non-POD classes. >(I recall some of these bugs were discussed in this newsgroup and on some >web forum.) > >Moreover, you can easily compose std::vector with other containers (e.g. you >could simply build a vector<vector>). > >And vector has a better dynamically-growth policy than CArray (not bad if >you store few items, but can make a difference for millions of items). >CArray uses arithmetic growth, which has a very bad O(N^2) asympotic >complexity; instead vector::push_back increases vector's capacity using a >1.5x factor, offering an amortized O(1) time. > > >> I am having a mental block with understanding the template >> declaration of >> template<class TYPE, class ARG_TYPE> >> What exactly is this saying ? The constructor is just CArray( ); > >Note that STL vector in its simplest form has only one template parameter, >i.e. the type you store in the vector, e.g. > > vector<int> someIntegers; > vector<MyStruct> collectionOfMyStructs; > >No need for the (useless and confusing, IMHO) ARG_TYPE thing. > >Using vector is very easy: > > #include <vector> // header file for std::vector > > // Creates an empty vector storing instances of MyClass > std::vector<MyClass> data; > > // Add some stuff > data.push_back( MyClass(...) ); > data.push_back( MyClass(...) ); > ... > >Use operator[] to retrieve vector elements (index is 0-based). > >And you can use resize() to change vector size. > >Other samples on using std::vector and description of its public methods can >be easily found using your favourite search engine. > >HTH, >Giovanni > Joseph M. Newcomer [MVP] email: newcomer(a)flounder.com Web: http://www.flounder.com MVP Tips: http://www.flounder.com/mvp_tips.htm
From: RB on 7 May 2010 17:06 Thanks I decided to take your advice since the vector sounds so much more versatile. However my compiler docs doesn't have much on this either, just linked refrences to the same declarations I am struggling to understand. I did find one search page that does give some examples at http://www.codeguru.com/cpp/cpp/cpp_mfc/stl/article.php/c4027 but my compiler doesn't want to compile some of the code samples. So I am pretty much still stuck. Below are the examples that won't compile (from the above link) . When I cut these out of my text, it compiles with zero errors. #include <vector> //... size_t size = 10; //<-error C2258: illegal pure syntax, must be '= 0' std::vector<int> array(size); //<- error C2252: 'size' : pure specifier can only be specified for functions // also error C2061: syntax error : identifier 'size' for(int i=0; i<size; ++i) //<-error C2059: syntax error : 'for' {array[i] = i;} // compiles with 180 errors but I think the rest are result from the above first 3. ---------Also this example will not compile #include <vector> //... std::vector<int> v(2); //<- error C2059: syntax error : 'constant' int& first = v.front(); //<-error C2327: 'CFileHandlingDoc::v' : member from enclosing class is not a type name, static, or enumerator //error C2065: 'v' : undeclared identifier //error C2228: left of '.front' must have class/struct/union type int& last = v.back(); //<-error C2252: 'last' : pure specifier can only be specified for functions
From: Giovanni Dicanio on 7 May 2010 17:23 "RB" <NoMail(a)NoSpam> ha scritto nel messaggio news:#kKrnki7KHA.1316(a)TK2MSFTNGP02.phx.gbl... >However my compiler docs doesn't have much > on this either, just linked refrences to the same declarations I am > struggling to understand. What compiler do you use? I recall VC6 had some problems with STL implementation, but using STLport (open source implementation of STL) fixed several of them. (Since VC7.1 there were big improvements.) > I did find one search page that does give some examples at > http://www.codeguru.com/cpp/cpp/cpp_mfc/stl/article.php/c4027 > but my compiler doesn't want to compile some of the code samples. > So I am pretty much still stuck. Below are the examples that won't > compile (from the above link) . When I cut these out of my text, it > compiles with zero errors. > > #include <vector> > //... > size_t size = 10; //<-error C2258: illegal pure syntax, > must be '= 0' ....it's like the compiler misinterprets 'size' like if it was a pure virtual method?! I believe you had some syntax errors. Please post your entire C++ source code to have a better diagnosis. Giovanni
From: Giovanni Dicanio on 7 May 2010 17:29 "RB" <NoMail(a)NoSpam> ha scritto nel messaggio news:#kKrnki7KHA.1316(a)TK2MSFTNGP02.phx.gbl... > #include <vector> > //... > size_t size = 10; //<-error C2258: illegal pure syntax, > must be '= 0' > std::vector<int> array(size); //<- error C2252: 'size' : pure specifier > can only be specified for functions > // also error C2061: syntax > error : identifier 'size' > for(int i=0; i<size; ++i) //<-error C2059: syntax error : 'for' > {array[i] = i;} > // compiles with 180 errors but I think the rest are result from the above > first 3. This small test code compiles just fine with VC10: <code> #include <vector> #include <iostream> using namespace std; int main() { size_t size = 10; vector<int> array(size); for (size_t i = 0; i < size; i++) { array[i] = i; } for (size_t j = 0; j < size; j++) { cout << array[j] << endl; } return 0; } </code> C:\TEMP>cl /EHsc /W4 test.cpp Microsoft (R) 32-bit C/C++ Optimizing Compiler Version 16.00.30319.01 for 80x86 Copyright (C) Microsoft Corporation. All rights reserved. test.cpp Microsoft (R) Incremental Linker Version 10.00.30319.01 Copyright (C) Microsoft Corporation. All rights reserved. /out:test.exe test.obj C:\TEMP>test.exe 0 1 2 3 4 5 6 7 8 9 Giovanni
From: RB on 7 May 2010 18:01
> What compiler do you use? > I recall VC6 had some problems with STL implementation, but using STLport (open source implementation of STL) fixed several of > them. > (Since VC7.1 there were big improvements.) Yes I am using VC6 and unfortunately I like it but this appears to be yet another reason to move on. I have two questions at this point. 1. Where can I get examples of this STLport ? 2. Can I install VS 2005 on the same machine without uninstalling my VC 6 ? |