Search Results

Search found 2886 results on 116 pages for 'std'.

Page 84/116 | < Previous Page | 80 81 82 83 84 85 86 87 88 89 90 91  | Next Page >

  • Using * Width & Precision Specifiers With boost::format

    - by John Dibling
    I am trying to use width and precision specifiers with boost::format, like this: #include <boost\format.hpp> #include <string> int main() { int n = 5; std::string s = (boost::format("%*.*s") % (n*2) % (n*2) % "Hello").str(); return 0; } But this doesn't work because boost::format doesn't support the * specifier. Boost throws an exception when parsing the string. Is there a way to accomplish the same goal, preferably using a drop-in replacement?

    Read the article

  • 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.

    Read the article

  • C++ runtime, display exception message

    - by aaa
    hello. I am using gcc on linux to compile C++ code. There are some exceptions which should not be handled and should close program. However, I would like to be able to display exception string: For example: throw std::runtime_error(" message"); does not display message, only type of error. I would like to display messages as well. Is there way to do it? it is a library, I really do not want to put catch statements and let library user decide. However, right now library user is fortran, which does not allow to handle exceptions. in principle, I can put handlers in wrapper code, but rather not to if there is a way around Thanks

    Read the article

  • How do C++ header files work?

    - by PulpFiction
    Hi all. When I include some function from a header file in a C++ program, does the entire header file code get copied to the final executable or only the machine code for the specific function is generated. For example, if I call std::sort from the <algorithm> header in C++, is the machine code generated only for the sort() function or for the entire <algorithm> header file. I think that a similar question exists somewhere on Stack Overflow, but I have tried my best to find it (I glanced over it once, but lost the link). If you can point me to that, it would be wonderful.

    Read the article

  • Evaluation of (de)reference operators

    - by Micha
    I have an (uncommented...) source file which I'm trying to understand. static const Map *gCurMap; static std::vector<Map> mapVec; then auto e = mapVec.end(); auto i = mapVec.begin(); while(i!=e) { // ... const Map *map = gCurMap = &(*(i++)); // ... } I don't understand what &(*(i++)) does. It does not compile when just using i++, but to me it looks the same, because I'm "incrementing" i, then I'm requesting the value at the given address and then I'm requesting the address of this value?!

    Read the article

  • delegating into private parts

    - by FredOverflow
    Sometimes, C++'s notion of privacy just baffles me :-) class Foo { struct Bar; Bar* p; public: Bar* operator->() const { return p; } }; struct Foo::Bar { void baz() { std::cout << "inside baz\n"; } }; int main() { Foo::Bar b; // error: 'struct Foo::Bar' is private within this context Foo f; f->baz(); // fine } Since Foo::Bar is private, I cannot declare b in main. Yet I can call methods from Foo::Bar just fine. Why the hell is this allowed? Was that an accident or by design?

    Read the article

  • can we write this in C++ switch ?

    - by jellly
    #include <iostream> using namespace std; int main(){ char i; cin >>i; switch (i){ case ('e'||'i'||'o'||'u'||'a'): cout<<"Vowel"; break; case ('+'||'-'||'/'||'*'||'%'): cout<<"Op"; break; } return 0; } if not than how can we use comparison or logical operators in switch ? & why cant we declare and initialize variable in single case without using scope ?

    Read the article

  • Normal C++ code in Qt doesnt build and run

    - by Nick
    Hello. I am using Qt under linux, if it matters. I ran successfully under Geany (a simple c++ compiler) the following: //my first program in C++ Hello World! include using namespace std; int main () {cout << "Hello World!"; return 0;} I opened Qt source file and copied the exact same code and i can't build or run. Thank you for your responses to this simple problem.

    Read the article

  • Another problem with decltype

    - by There is nothing we can do
    template<class IntT, IntT low = IntT(), IntT high = IntT()> struct X { static_assert(std::is_same<decltype(low),decltype(high)>::value,"Different types not allowed");//this should give error if types are different decltype(low) a; decltype(high) b; X():a(decltype(a)()),b(decltype(b)())//WHY THIS DOES NOT COMPILE? { cout << typeid(a).name() << '\n'; cout << typeid(b).name() << '\n'; } }; int _tmain(int argc, _TCHAR* argv[]) { X<char,1,'a'> x;//this according to static_assert shouldn't compile but it does return 0; } Using VS2010. Please see 3 comments in code above.

    Read the article

  • Why I have to redeclare a virtual function while overriding [C++]

    - by Neeraj
    #include <iostream> using namespace std; class Duck { public: virtual void quack() = 0; }; class BigDuck : public Duck { public: // void quack(); (uncommenting will make it compile) }; void BigDuck::quack(){ cout << "BigDuckDuck::Quack\n"; } int main() { BigDuck b; Duck *d = &b; d->quack(); } Consider this code, the code doesn't compiles. However when I declare the virtual function in the subclass, then it compiles fine. The compiler already has the signature of the function which the subclass will override, then why a redeclaration is required? Any insights.

    Read the article

  • Shuffle array variables in a pre-specified order, without using extra memory of "size of input array"

    - by Eternal Learner
    Input : A[4] = {0,4,-1,1000} - Actual Array P[4] = {1,0,3,2} - Order to be reshuffled Output: A[4] = {4,0,1000,-1} Condition : Don't use an additional array as memory. Can use an extra variable or two. Problem : I have the below program in C++, but this fails for certain inputs of array P. #include<iostream> using namespace std; void swap(int *a_r,int *r) { int temp = *r; *r = *a_r; *a_r = temp; } int main() { int A[4] = {0,4,-1,1000}; int P[4] = {3,0,1,2}; int value = A[0] , dest = P[0]; for(int i=0; i<4;i++) { swap(&A[dest],&value); dest = P[dest]; } for(int i=0;i<4;i++) cout<<A[i]<<" "; }

    Read the article

  • Basic C++ code for multiplication of 2 matrix or vectors (C++ beginner)

    - by Ice
    I am a new C++ user and I am also doing a major in Maths so thought I would try implement a simple calculator. I got some code off the internet and now I just need help to multiply elements of 2 matrices or vectors. Matrixf multiply(Matrixf const& left, Matrixf const& right) { // error check if (left.ncols() != right.nrows()) { throw std::runtime_error("Unable to multiply: matrix dimensions not agree."); } /* I have all the other part of the code for matrix*/ /** Now I am not sure how to implement multiplication of vector or matrix.**/ Matrixf ret(1, 1); return ret; }

    Read the article

  • Can nohup change the result of a C++ code?

    - by Biga
    I am having this very weird behaviour with a C++ code: It gives me different results when running with and without 'nohup' (reproducible in cygwin and linux). I mean, if I get the same executable and run it like './run' or run it like 'nohup ./run out.log', I get different results! I use std::cout to output to screen, all lines ending with endl; I use ifstream for the input file; I use ofstream for output, all lines ending with endl. I am using g++ 4. Any idea what is going on?

    Read the article

  • C++ difference of keywords 'typename' and 'class' in templates

    - by Mat
    For templates I have seen both declarations: template < typename T > And: template < class T > What's the difference? And what exactly do those keywords mean in the following example (taken from the German Wikipedia article about templates)? template < template < typename, typename > class Container, typename Type > class Example { Container< Type, std::allocator < Type > > baz; };

    Read the article

  • Programmatically find maximum static array size in C++

    - by GuyGreer
    I am curious whether it is possible to determine the maximum size that an array can have in C++. #include <iostream> using namespace std; #define MAX 2000000 int main() { long array[MAX]; cout << "Message" << endl; return 0; } This compiles just fine, but then segfaults as soon as I run it (even though array isn't actually referenced). I know it's the array size too because if I change it to 1000000 it runs just fine. So, is there some define somewhere or some way of having #define MAX MAX_ALLOWED_ARRAY_SIZE_FOR_MY_MACHINE_DEFINED_SOMEWHERE_FOR_ME? I don't actually need this for anything, this question is for curiosity's sake.

    Read the article

  • Loop crashing program having to do with 2D arrays

    - by user450062
    I am creating an encoding program and when I instruct the program to create a 5X5 grid based on the alphabet while skipping over letters that match up to certain pre-defined variables(which are given values by user input during runtime). I have a loop that instructs the loop to keep running until the values that access the array are out of bounds, the loop seems to cause the problem. This code is standardized so there shouldn't be much trouble compiling it in another compiler. Also would it be better to seperate my program into functions? here is the code: #include<iostream> #include<fstream> #include<cstdlib> #include<string> #include<limits> using namespace std; int main(){ while (!cin.fail()) { char type[81]; char filename[20]; char key [5]; char f[2] = "q"; char g[2] = "q"; char h[2] = "q"; char i[2] = "q"; char j[2] = "q"; char k[2] = "q"; char l[2] = "q"; int a = 1; int b = 1; int c = 1; int d = 1; int e = 1; string cipherarraytemplate[5][5]= { {"a","b","c","d","e"}, {"f","g","h","i","j"}, {"k","l","m","n","o"}, {"p","r","s","t","u"}, {"v","w","x","y","z"} }; string cipherarray[5][5]= { {"a","b","c","d","e"}, {"f","g","h","i","j"}, {"k","l","m","n","o"}, {"p","r","s","t","u"}, {"v","w","x","y","z"} }; cout<<"Enter the name of a file you want to create.\n"; cin>>filename; ofstream outFile; outFile.open(filename); outFile<<fixed; outFile.precision(2); outFile.setf(ios_base::showpoint); cin.ignore(std::numeric_limits<int>::max(),'\n'); cout<<"enter your codeword(codeword can have no repeating letters)\n"; cin>>key; while (key[a] != '\0' ){ while(b < 6){ cipherarray[b][c] = key[a]; if ( f == "q" ) { cipherarray[b][c] = f; } if ( f != "q" && g == "q" ) { cipherarray[b][c] = g; } if ( g != "q" && h == "q" ) { cipherarray[b][c] = h; } if ( h != "q" && i == "q" ) { cipherarray[b][c] = i; } if ( i != "q" && j == "q" ) { cipherarray[b][c] = j; } if ( j != "q" && k == "q" ) { cipherarray[b][c] = k; } if ( k != "q" && l == "q" ) { cipherarray[b][c] = l; } a++; b++; } c++; b = 1; } while (c < 6 || b < 6){ if (cipherarraytemplate[d][e] == f || cipherarraytemplate[d][e] == g || cipherarraytemplate[d][e] == h || cipherarraytemplate[d][e] == i || cipherarraytemplate[d][e] == j || cipherarraytemplate[d][e] == k || cipherarraytemplate[d][e] == l){ d++; } else { cipherarray[b][c] = cipherarraytemplate[d][e]; d++; b++; } if (d == 6){ d = 1; e++; } if (b == 6){ c++; b = 1; } } cout<<"now enter some text."<<endl<<"To end this program press Crtl-Z\n"; while(!cin.fail()){ cin.getline(type,81); outFile<<type<<endl; } outFile.close(); } } I know there is going to be some mid-forties guy out there who is going to stumble on to this post, he's have been programming for 20-some years and he's going to look at my code and say: "what is this guy doing".

    Read the article

  • Getting input in system() function (Mac)

    - by Alex
    #include <iostream> using namespace std; int main() { short int enterVal; cout << "enter a number to say: " << endl; cin >> enterVal; system("say "%d"") << enterVal; return 0; } Is what I am currently trying. I want the user to enter a number and the system() function says it basically. The code above has an error which says " 'd' was not declared in this scope ". Thanks in advance.

    Read the article

  • [C++] which is better, throw an exception or return nonzero value?

    - by xis19
    While you are doing C++ programming, you have two choices of reporting an error. I suppose many teachers would suggest you throw an exception, which is derived from std::exception. Another way, which might be more "C" style, is to return a non-zero value, as zero is "ERROR_SUCCESS". Definitively, return an exception can provide much more information of the error and recovery; while the code will bloat a little bit, and making exception-safe in your mind is a little difficult for me, at least. Other way like returning something else, will make reporting an error much easier; the defect is that managing recovery will be a possibly big problem. So folks, as good programmers, which would be your preference, not considering your boss' opinion? For me, I would like to return some nonzero values.

    Read the article

  • Make object by it's name

    - by Ockonal
    Hello, is it possible to return exemplar of object using passed type name (string) in c++? I have some base abstract class Base and a few derivates. Example code: class Base { /* ... */ }; class Der1 : public Base { /* ... */ }; class Der2 : public Base { /* ... */ }; And I need function like: Base *objectByType(const std::string &name); Number of derivates classes are changeable and I don't want to make something like switching of name and returning by hands new object type. Is it possible in c++ to do that automatically anyway? p.s. usage should looks like: dynamic_cast<Der1>(objectByType("Der1")); I need pure c++ code (crossplatform). Using boost is permissible.

    Read the article

  • C++ Boost bind value type {solved}

    - by aaa
    hello. I look in documentation and source code but cannot figure out how to get return value type of boost bind functor. I am trying to accomplish following: 35 template<typename T,size_t N, class F> 36 boost::array<typename F::value_type, N> make_array(T (&input)[N], F unary) { 37 boost::array<typename F::value_type, N> array; 38 std::transform(input, input + N, array.begin(), unary); 39 return array; 40 } where F can be bind functor. the above does not work because functor does not have value_type. for that matter, is there standard interface for unary/binary functor as far as return value. solution: it should be result_type. also equivalent defined are argument_type and first/second_argument_type for binary functions Thanks

    Read the article

  • Why does the Win32-API have so many custom types?

    - by sub
    I'm new to the Win32 API and the many new types begin to confuse me. Some functions take 1-2 ints and 3 UINTS as arguments. Why can't they just use ints? What are UINTS? Then, there are those other types: DWORD LPCWSTR LPBOOL Again, I think the "primitive" C types would be enough - why introduce 100 new types? This one was a pain: WCHAR* I had to iterate through it and push_back every character to an std::string as there wasn't another way to convert it to one. Horrible. Why WCHAR? Why reinvent the wheel? They could have just used char* instead, or?

    Read the article

  • Problem with Initializing Consts

    - by UdiM
    This code, when compiled in xlC 8.0 (on AIX 6.1), produces the wrong result. It should print 12345, but instead prints 804399880. Removing the const in front of result makes the code work correctly. Where is the bug? #include <stdio.h> #include <stdlib.h> #include <string> long int foo(std::string input) { return strtol(input.c_str(), NULL, 0); } void bar() { const long int result = foo("12345"); printf("%u\n", result); } int main() { bar(); return 0; } Compilation command: /usr/vacpp/bin/xlC example.cpp -g

    Read the article

  • C++ a map to a 2 dimensional vector

    - by user1701545
    I want to create a C++ map where key is, say, int and value is a 2-D vector of double: map myMap; suppose I filled it and now I would like to update the second vector mapped by each key (for example divide each element by 2). How would I access that vector iteratively? The "itr-second[0]" syntax in the statement below is obviously wrong. What would be the right syntax for that action? for(std::map<in, vector<vector<double> > > itr = myMap.begin(); itr != myMap.end();++itr) { for(int i = 0;i < itr->second[0].size();++i) { itr->second[0][i] /= 2; } } thanks, rubi

    Read the article

  • Compilation failing - no #include - boost

    - by jwoolard
    Hi, I'm trying to compile a third-party library, but g++ is complaining about the following line: typedef boost::shared_ptr<MessageConsumer> MessageConsumerPtr; The strange thing is, there is no #include directive in the file - and it is clearly supposed to be this way; there are about 60 files with the same (or very similar) issues. Clearly if there was an #include directive referencing the relevant boost header this would compile cleanly. My question is: how can I get g++ to somehow automagically find the relevant symbol (in all instances of this issue, it is a namespace that can't be found - usually std:: or boost::) by either automatically processing the relevant header (or some other mechanism). Thanks. Edit My current g++ call looks like: g++ -fPIC -O3 -DUSING_PCH -D_REENTRANT -I/usr/include/boost -I./ -c MessageInterpreter.cpp -o MessageInterpreter.o

    Read the article

  • Misunderstanding function pointer - passing it as an argument

    - by Stef
    I want to pass a member function of class A to class B via a function pointer as argument. Please advise whether this road is leading somewhere and help me fill the pothole. #include <iostream> using namespace std; class A{ public: int dosomeA(int x){ cout<< "doing some A to "<<x <<endl; return(0); } }; class B{ public: B(int (*ptr)(int)){ptr(0);}; }; int main() { A a; int (*APtr)(int)=&A::dosomeA; B b(APtr); return 0; } This brilliant piece of code leaves me with the compiler error: cannot convert int (A::*)(int)' toint (*)(int)' in initialization Firstly I want it to compile. Secondly I don't want dosomeA to be STATIC.

    Read the article

< Previous Page | 80 81 82 83 84 85 86 87 88 89 90 91  | Next Page >