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  • Threading and pcap issues.

    - by cftmon
    I have a GUI program that allows a user a scan a network, the issue is that when the pcap_loop function is called, my GUI program becomes unresponsive.(the pcap_loop blocks the current thread). When i try to use pthreads, i got a SIGSEGV fault at the pcap_loop function.Why?It's as if the thread can't see the procPacket function itself. void procPacket(u_char *arg, const struct pcap_pkthdr *pkthdr, const u_char *packet) { //show packets here } void* pcapLooper(void* param) { pcap_t* handler = (pcap_t*) param; pcap_loop(handler, 900 ,procPacket, NULL ); } //some function that runs when a button is pressed //handler has been opened through pcap_open_live pthread_t scanner; int t = pthread_create(&scanner,NULL,&pcapLooper, &handler ); if(t) { std::cout << "failed" << std::endl; } pthread_join(scanner,NULL); //do other stuff.

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  • Some clarification on rvalue references

    - by Dennis Zickefoose
    First: where are std::move and std::forward defined? I know what they do, but I can't find proof that any standard header is required to include them. In gcc44 sometimes std::move is available, and sometimes its not, so a definitive include directive would be useful. When implementing move semantics, the source is presumably left in an undefined state. Should this state necessarily be a valid state for the object? Obviously, you need to be able to call the object's destructor, and be able to assign to it by whatever means the class exposes. But should other operations be valid? I suppose what I'm asking is, if your class guarantees certain invariants, should you strive to enforce those invariants when the user has said they don't care about them anymore? Next: when you don't care about move semantics, are there any limitations that would cause a non-const reference to be preferred over an rvalue reference when dealing with function parameters? void function(T&); over void function(T&&); From a caller's perspective, being able to pass functions temporary values is occasionally useful, so it seems as though one should grant that option whenever it is feasible to do so. And rvalue references are themselves lvalues, so you can't inadvertently call a move-constructor instead of a copy-constructor, or something like that. I don't see a downside, but I'm sure there is one. Which brings me to my final question. You still can not bind temporaries to non-const references. But you can bind them to non-const rvalue references. And you can then pass along that reference as a non-const reference in another function. void function1(int& r) { r++; } void function2(int&& r) { function1(r); } int main() { function1(5); //bad function2(5); //good } Besides the fact that it doesn't do anything, is there anything wrong with that code? My gut says of course not, since changing rvalue references is kind of the whole point to their existence. And if the passed value is legitimately const, the compiler will catch it and yell at you. But by all appearances, this is a runaround of a mechanism that was presumably put in place for a reason, so I'd just like confirmation that I'm not doing anything foolish.

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  • Is there a way to access the locale used by gettext under windows ?

    - by phtrivier
    I have a program where i18n is handled by gettext. The program works fine, however for some reason I need to know the name of the locale used by gettext at runtime (something like 'fr_FR') under win32. I looked into gettext sources, and there is a quite frightening function that computes it on all platforms (gl_locale_name, in a C file called "localename.h/c"). However, this file does not seem to be installed alongside gettext or libintl, so I can't seem to call the function. Is there another function provided by gettext to get this value ? Or in another package (boost, glib, anything ?) (On a related note, there is a thing called std::locale in the C++ standard library, and according to the doc calling std::locale("") should create a locale with the settings of the system, unless I am mistaken ... but then the name is 'C' under windows. Is it a viable way of getting the locale name ? What I am doing wrong ?)

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  • Boost multiindex complex struct

    - by StrifeLow
    In boost multiindex example complex_structs, it use one key in the car_manufacturer struct for car_table. If car_manufacturer have been modify to have 2 ID struct car_manufacturer { std::string name; int cm_code; car_manufacturer(const std::string& name_, const int& cm_code_):name(name_), cm_code(cm_code_){} }; What will be the key_from_key struct looks like? Have try to add another KeyExtractor or use composite index inside key_from_key, but still cannot compile. Please help on this. Thanks.

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  • Pointing to vectors

    - by Matt Munson
    #include <iostream> #include <vector> using namespace std; int main () { vector <int> qwerty; qwerty.push_back(5); vector <int>* p = &qwerty; cout << p[0]; //error: no match for 'operator<<' in 'std::cout << * p' } I'm generally unclear on how to use pointers with vectors, so I'm pretty mystified as to why this is not working. To my mind, this should print 5 to screen.

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  • how to copy char * into a string and visa versa

    - by user295030
    If i pass a char * into a function. I want to then take that char * convert it to a std::string and once I get my result convert it back to char * from a std::string to show the result. I don't know how to do this for conversion ( I am not talking const char * but just char *) I am not sure how to manipulate the value of the pointer I send in. so steps i need to do take in a char * convert it into a string. take the result of that string and put it back in the form of a char * return the result such that the value should be available outside the function and not get destroyed. If possible can i see how it could be done via reference vs a pointer (whose address I pass in by value however I can still modify the value that pointer is pointing to. so even though the copy of the pointer address in the function gets destroyed i still see the changed value outside. thanks!

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  • Splitting a double vector into equal parts

    - by Cosmin
    Greetings, Any input on a way to divide a std::vector into two equal parts ? I need to find the smallest possible difference between |part1 - part2|. This is how I'm doing it now, but from what you can probably tell it will yield a non-optimal split in some cases. auto mid = std::find_if(prim, ultim, [&](double temp) -> bool { if(tempsum >= sum) return true; tempsum += temp; sum -= temp; return false; }); The vector is sorted, highest to lowest, values can indeed appear twice. I'm not expecting part1 and part2 to have the same numbers of elements, but sum(part1) should be as close as possible to sum(part2) For example if we would have { 2.4, 0.12, 1.26, 0.51, 0.70 }, the best split would be { 2.4, 0.12 } and { 1.26, 0.51, 0.70 }. If it helps, I'm trying to achieve the splitting algorithm for the Shannon Fano encoding. Any input is appreciated, thanks!

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  • numpy array C api

    - by wiso
    I have a C++ function returning a std::vector and I want to use it in python, so I'm using the C numpy api: static PyObject * py_integrate(PyObject *self, PyObject *args){ ... std::vector<double> integral; cpp_function(integral); // this change integral npy_intp size = {integral.size()}; PyObject *out = PyArray_SimpleNewFromData(1, &size, NPY_DOUBLE, &(integral[0])); return out; } when I call it from python, if I do import matplotlib.pyplot as plt a = py_integrate(parameters) print a fig = plt.figure() ax = fig.add_subplot(111) ax.plot(a) print a the first print is ok, the values are correct, but when I plot a they are not, and in particular in the second print I see very strange values like 1E-308 1E-308 ... or 0 0 0 ... as an unitialized memory. I don't understand why the first print is ok.

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  • Why are gettimeofday() intervals occasionally negative?

    - by Andres Jaan Tack
    I have an experimental library whose performance I'm trying to measure. To do this, I've written the following: struct timeval begin; gettimeofday(&begin, NULL); { // Experiment! } struct timeval end; gettimeofday(&end, NULL); // Print the time it took! std::cout << "Time: " << 100000 * (end.tv_sec - begin.tv_sec) + (end.tv_usec - begin.tv_usec) << std::endl; Occasionally, my results include negative timings, some of which are nonsensical. For instance: Time: 226762 Time: 220222 Time: 210883 Time: -688976 What's going on?

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  • Programmatically create static arrays at compile time in C++

    - by Hippicoder
    One can define a static array at compile time as follows: const std::size_t size = 5; unsigned int list[size] = { 1, 2, 3, 4, 5 }; Question 1 - Is it possible by using various kinds of metaprogramming techniques to assign these values "programmatically" at compile time? Question 2 - Assuming all the values in the array are to be the same barr a few, is it possible to selectively assign values at compile time in a programmatic manner? eg: const std::size_t size = 7; unsigned int list[size] = { 0, 0, 2, 3, 0, 0, 0 }; Solutions using C++0x are welcome The array may be quite large, few hundred elements long The array for now will only consist of POD types It can also be assumed the size of the array will be known beforehand, in a static compile-time compliant manner. Solutions must be in C++ (no script or codegen based solutions)

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  • Passing a template func. as a func. ptr to an overloaded func. - is there a way to compile this code

    - by LoudNPossiblyRight
    Just a general c++ curiosity: This code below shouldn't compile because it's impossible to know which to instantiate: temp(const int&) or temp(const string&) when calling func(temp) - this part i know. What i would like to know is if there is anything i can do to the line marked PASSINGLINE to get the compiler to deduce that i want FPTR1 called and not FPTR2 ? #include<iostream> using std::cout; using std::endl; /*FPTR1*/ void func(void(*fptr)(const int&)){ fptr(1001001);} /*FPTR2*/ void func(void(*fptr)(const string&)){ fptr("1001001"); } template <typename T> void temp(const T &t){ cout << t << endl; } int main(){ /*PASSINGLINE*/ func(temp); return 0; } Thank you.

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  • STL map containing references does not compile

    - by MTsoul
    The following: std::map<int, ClassA &> test; gives: error C2101: '&' on constant While the following std::map<ClassA &, int> test; gives error C2528: '_First' : pointer to reference is illegal The latter seems like map cannot contain a reference for the key value, since it needs to instantiate the class sometimes and a reference cannot be instantiated without an object. But why does the first case not work?

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  • Initializing structs in C++

    - by Neil Butterworth
    As an addendum to this question, what is going on here: #include <string> using namespace std; struct A { string s; }; int main() { A a = {0}; } Obviously, you can't set a std::string to zero. Can someone provide an explanation (backed with references to the C++ Standard, please) about what is actually supposed to happen here? And then explain for example): int main() { A a = {42}; } Are either of these well-defined? Once again an embarrassing question for me - I always give my structs constructors, so the issue has never arisen before.

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  • C++: Best text accumulator

    - by MInner
    Text gets accumulates piecemeal before being sent to client. Now we use own class that allocates memory for each piece as char massive. (Anyway, works like char[][] + std::list<char*>). Then we build the whole string, convert it into std::sting and then create boost::asio::streambuf using it. That's slow enough, I assume. Correct me if I'm wrong. I know, in many cases simple FILE type from stdio.h is used. How does it works? Allocates memory at every write into it. So, is it faster and is there any way to read into boost::asio::streambuf from FILE?

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  • zlib gzgets extremely slow?

    - by monkeyking
    I'm doing stuff related to parsing huge globs of textfiles, and was testing what input method to use. There is not much of a difference using c++ std::ifstreams vs c FILE, According to the documentation of zlib, it supports uncompressed files, and will read the file without decompression. I'm seeing a difference from 12 seconds using non zlib to more than 4 minutes using zlib.h This I've tested doing multiple runs, so its not a disk cache issue. Am I using zlib in some wrong way? thanks #include <zlib.h> #include <cstdio> #include <cstdlib> #include <fstream> #define LENS 1000000 size_t fg(const char *fname){ fprintf(stderr,"\t-> using fgets\n"); FILE *fp =fopen(fname,"r"); size_t nLines =0; char *buffer = new char[LENS]; while(NULL!=fgets(buffer,LENS,fp)) nLines++; fprintf(stderr,"%lu\n",nLines); return nLines; } size_t is(const char *fname){ fprintf(stderr,"\t-> using ifstream\n"); std::ifstream is(fname,std::ios::in); size_t nLines =0; char *buffer = new char[LENS]; while(is. getline(buffer,LENS)) nLines++; fprintf(stderr,"%lu\n",nLines); return nLines; } size_t iz(const char *fname){ fprintf(stderr,"\t-> using zlib\n"); gzFile fp =gzopen(fname,"r"); size_t nLines =0; char *buffer = new char[LENS]; while(0!=gzgets(fp,buffer,LENS)) nLines++; fprintf(stderr,"%lu\n",nLines); return nLines; } int main(int argc,char**argv){ if(atoi(argv[2])==0) fg(argv[1]); if(atoi(argv[2])==1) is(argv[1]); if(atoi(argv[2])==2) iz(argv[1]); }

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  • is memset(ary,0,length) a portable way of inputting zero in double array

    - by monkeyking
    The following code uses memset to set all the bits to zero #include <iostream> #include <cstring> int main(){ int length = 5; double *array = new double[length]; memset(array,0,sizeof(double)*length); for(int i=0;i<length;i++) if(array[i]!=0.0) std::cerr<< "not zero in: " <<i <<std::endl; return 0; } Can I assume that this will work on all platforms? Does the double datatype always correspond to the ieee-754 standard? thanks

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  • Do I need multiple template specializations if I want to specialize for several kinds of strings?

    - by romkyns
    For example: template<typename T> void write(T value) { mystream << value; } template<> void write<const char*>(const char* value) { write_escaped(mystream, value); } template<> void write<char*>(char* value) { write_escaped(mystream, value); } template<> void write<std::string>(std::string value) { write_escaped(mystream.c_str(), value); } This looks like I'm doing it wrong, especially the two variants for const and non-const char*. However I checked that if I only specialize for const char * then passing a char * variable will invoke the non-specialized version, when called like this in VC++10: char something[25]; strcpy(something, "blah"); write(something); What would be the proper way of doing this?

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  • C++ Code Clarification Needed..

    - by ke3pup
    Hi guys I'm trying to understand what the code below says: struct compare_pq; struct compare_pq { bool operator() (Events *& a, Events *& b); }; std::priority_queue<Events *, std::vector<Events *>, compare_pq> eventList; i looked at what priority_queue is and how its declared but can't quit understand what compare_pq is doing in the priority_queue eventList. Also what does operator() do since i've never seen *& before and empty operator overloading operator()! any help would be appreciated. Thank you

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  • Netbeans C++ not finding standard libraries (Macintosh)

    - by Grue
    Hello everyone! I am trying to use Netbeans 6.7 (on a Mac) to create C++ applications. I started out with the standard "Hello World," just to test if everything was working correctly. First try std and could not be found. So I tried reinstalling the developer tools on my Mac OS X disk. After that Netbeans updated its c++ compiler info, but still cannot find std or . Odder than this XCode seems to be working with C++ perfectly fine. Any help fixing this would be greatly appreciated.

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  • How do you use C++0x raw strings with GCC 4.5?

    - by Rob N
    This page says that GCC 4.5 has C++ raw string literals: http://gcc.gnu.org/projects/cxx0x.html But when I try to use the syntax from this page: http://www2.research.att.com/~bs/C++0xFAQ.html#raw-strings #include <iostream> #include <string> using namespace std; int main() { string s = R"[\w\\\w]"; } I get this error: /opt/local/bin/g++-mp-4.5 -std=gnu++0x -O3 rawstr.cc -o rawstr rawstr.cc:9:19: error: invalid character '\' in raw string delimiter rawstr.cc:9:5: error: stray 'R' in program What is the right syntax for raw strings?

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  • Avoid warning 'Unreferenced Formal Parameter'

    - by bdhar
    I have a super class like this: class Parent { public: virtual void Function(int param); }; void Parent::Function(int param) { std::cout << param << std::endl; } ..and a sub-class like this: class Child : public Parent { public: void Function(int param); }; void Child::Function(int param) { ;//Do nothing } When I compile the sub-class .cpp file, I get this error warning C4100: 'param' : unreferenced formal parameter As a practise, we used to treat warnings as errors. How to avoid the above warning? Thanks.

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  • Problem separating C++ code in header, inline functions and code.

    - by YuppieNetworking
    Hello all, I have the simplest code that I want to separate in three files: Header file: class and struct declarations. No implementations at all. Inline functions file: implementation of inline methods in header. Code file: normal C++ code for more complicated implementations. When I was about to implement an operator[] method, I couldn't manage to compile it. Here is a minimal example that shows the same problem: Header (myclass.h): #ifndef _MYCLASS_H_ #define _MYCLASS_H_ class MyClass { public: MyClass(const int n); virtual ~MyClass(); double& operator[](const int i); double operator[](const int i) const; void someBigMethod(); private: double* arr; }; #endif /* _MYCLASS_H_ */ Inline functions (myclass-inl.h): #include "myclass.h" inline double& MyClass::operator[](const int i) { return arr[i]; } inline double MyClass::operator[](const int i) const { return arr[i]; } Code (myclass.cpp): #include "myclass.h" #include "myclass-inl.h" #include <iostream> inline MyClass::MyClass(const int n) { arr = new double[n]; } inline MyClass::~MyClass() { delete[] arr; } void MyClass::someBigMethod() { std::cout << "Hello big method that is not inlined" << std::endl; } And finally, a main to test it all: #include "myclass.h" #include <iostream> using namespace std; int main(int argc, char *argv[]) { MyClass m(123); double x = m[1]; m[1] = 1234; cout << "m[1]=" << m[1] << endl; x = x + 1; return 0; } void nothing() { cout << "hello world" << endl; } When I compile it, it says: main.cpp:(.text+0x1b): undefined reference to 'MyClass::MyClass(int)' main.cpp:(.text+0x2f): undefined reference to 'MyClass::operator[](int)' main.cpp:(.text+0x49): undefined reference to 'MyClass::operator[](int)' main.cpp:(.text+0x65): undefined reference to 'MyClass::operator[](int)' However, when I move the main method to the MyClass.cpp file, it works. Could you guys help me spot the problem? Thank you.

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  • How to reduce redundant code when adding new c++0x rvalue reference operator overloads

    - by Inverse
    I am adding new operator overloads to take advantage of c++0x rvalue references, and I feel like I'm producing a lot of redundant code. I have a class, tree, that holds a tree of algebraic operations on double values. Here is an example use case: tree x = 1.23; tree y = 8.19; tree z = (x + y)/67.31 - 3.15*y; ... std::cout << z; // prints "(1.23 + 8.19)/67.31 - 3.15*8.19" For each binary operation (like plus), each side can be either an lvalue tree, rvalue tree, or double. This results in 8 overloads for each binary operation: // core rvalue overloads for plus: tree operator +(const tree& a, const tree& b); tree operator +(const tree& a, tree&& b); tree operator +(tree&& a, const tree& b); tree operator +(tree&& a, tree&& b); // cast and forward cases: tree operator +(const tree& a, double b) { return a + tree(b); } tree operator +(double a, const tree& b) { return tree(a) + b; } tree operator +(tree&& a, double b) { return std::move(a) + tree(b); } tree operator +(double a, tree&& b) { return tree(a) + std::move(b); } // 8 more overloads for minus // 8 more overloads for multiply // 8 more overloads for divide // etc which also has to be repeated in a way for each binary operation (minus, multiply, divide, etc). As you can see, there are really only 4 functions I actually need to write; the other 4 can cast and forward to the core cases. Do you have any suggestions for reducing the size of this code? PS: The class is actually more complex than just a tree of doubles. Reducing copies does dramatically improve performance of my project. So, the rvalue overloads are worthwhile for me, even with the extra code. I have a suspicion that there might be a way to template away the "cast and forward" cases above, but I can't seem to think of anything.

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