function-pointers

问题 A quick question I hope. I would like to know why the line commented out below causes an error when placed at the global level while it works fine when placed inside the main function? Many Thanks #include <iostream> using namespace std; bool compare(const int &v1, const int &v2) { if (v1 < v2) { return true; } else { return false; } } bool (*pf5)(const int &v1, const int &v2); //pf5 = compare; int main() { int v1 = 5; int v2 = 6; pf5 = compare; bool YesNo1 = compare(v1, v2); cout << YesNo1 <

问题 I just dont get it, why line 22 is failing to compile? #include <stdexcept> #include <dlfcn.h> #include "Library.h" int main(int argc, char *argv[]) { try { void* libHandle = 0; libHandle = dlopen("libExpandableTestLibrary.so", RTLD_LAZY); if(!libHandle) throw std::logic_error(dlerror()); std::cout << "Libary opened gracefully" << std::endl; void* fuPtr = 0; fuPtr = dlsym(libHandle, "createLibrary"); if(!fuPtr) throw std::logic_error(dlerror()); Library* libInstance = static_cast<Library* ()>

问题 I am working on a universal app that should be able to run on iPad and iPhone. The Apple iPad docs say to use UI_USER_INTERFACE_IDIOM() to check if I am running on iPad or iPhone, but our iPhone is 3.1.2 and will not have UI_USER_INTERFACE_IDIOM() defined. As such, this code breaks: //iPhone should not be flipped upside down. iPad can have any - (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation { if(UI_USER_INTERFACE_IDIOM() == UIUserInterfaceIdiomPad)

问题 I'm new in programming and learning pointers in array in C. Have a look at the below programmes. 1st program #include<stdio.h> int fun(); int main() { int num[3][3]={21,325,524,52,0,6514,61,33,85}; fun(num); printf("%d",*(*(num+1)+1)); *(*(num+1)+1)=0; printf("%d",*(*(num+1)+1)); return 0; } int fun(int **p) { *(*(p+1)+1)=2135; return 0; } 2nd program #include<stdio.h> int fun(); int main() { int num[3][3]={21,325,524,52,0,6514,61,33,85}; fun(num); printf("%d",*(*(num+1)+1)); *(*(num+1)+1)=0;

问题 I am working on a pipeline-like design pattern. One of my design goals is to enable dynamic linking of pipeline segments by providing pointers to function members of a certain data class. Each of the data classes has a set of function members (representing the data class output ports) indexed using an integer template argument. These functions deduce the return type dynamically using keyword auto , but all accept the same integer argument c_Idx , i.e. template <int N> auto getOutput(int c_Idx

问题 I have a sanitization function that I want to run on (traditional) pointer types only. My problem is with function templates I can get as far as limiting the function to only pointers, however because of casting rule differences between function pointers and regular pointers, I run into problems. The Sanitize() function needs to run against a whole slew of types, some of which are pointers and need to be sanitized, others of which are function pointers of varying arity and parameter types and

问题 I have dug around quite a bit today and have come up empty. Is there any way to store a functor that is returned from a boost::bind with different types? I found an example that used boost::variants but not sure that this is needed. (Foo and Bar have been simplified for simplicity sake) #include <boost/bind.hpp> #include <boost/variant.hpp> #include <boost/function.hpp> #include <map> #include <iostream> template <typename FooType> struct Foo { const FooType tmp_value; Foo(const FooType& tmp_

问题 Googling for C++ functor syntax brings a lot of different results and I don't think I see what need in any of them. Some use templates, some use a single class, others multiple, and still others use structs instead. I'm never sure what specific elements I need for what I want to do. So now, what I want to do: I have two functions. They both take the exact same parameters, but are named differently and will return a different result, though the return type is also the same, e.g., unsigned foo1

问题 is it possible, like this: template< typename C, typename R, typename A, typename F=R (C::*)(A) > class MemberFuncPtr { ... 回答1: Actually,it seems pretty right to me, I do not get any errors for this piece of code: template< typename C, typename R, typename A, typename F=R (C::*)(A) > class MemberFuncPtr { C & Cmember; F f; public: MemberFuncPtr(C & c, F func):Cmember(c), f(func) {} R DoIt(A & a) { return (Cmember.*f)(a); } }; class classA { public: int toInt(double aa) { return int(aa); } };

问题 I know that declaring a function (or function pointer) with no parameter list (and without specifying void in the parameter list) that means that the function (or function pointer) has an unknown number of arguments. I wrote some test scripts to check this behavior out: int my_func_1() { return(0); } int my_func_2(int x) { return(x); } int my_func_3(char x, ...) { va_list va; va_start(va, x); return(va_arg(va, int)); } int (*fp)(); fp = my_func_1; printf("%d\n", fp()); fp = my_func_2; printf(