问题
So I have this code:
#include "boost_bind.h"
#include <math.h>
#include <vector>
#include <algorithm>
double foo(double num, double (*func)(double)) {
return 65.4;
}
int main(int argc, char** argv) {
std::vector<double> vec;
vec.push_back(5.0);
vec.push_back(6.0);
std::transform(vec.begin(), vec.end(), vec.begin(), boost::bind(foo, _1, log));
}
And receive this error:
return unwrapper<F>::unwrap(f, 0)(a[base_type::a1_], a[base_type::a2_]);
.............................................................^
%CXX-E-INCOMPATIBLEPRM, argument of type "double (* __ptr64 )(double) C" is
incompatible with parameter of type "double (* __ptr64 )(double)"
detected during:
instantiation of ...5 pages of boost
So this error is because 'log' is extern "C"'d in math.h
I was wondering how to declare my function pointer argument in foo() so it handles extern "C"'d functions.
回答1:
You can try including cmath
instead, and using static_cast<double(*)(double)>(std::log)
(cast necessary to resolve to the double
overload).
Otherwise, you will limit your function to extern C
functions. This would work like
extern "C" typedef double (*ExtCFuncPtr)(double);
double foo(double num, ExtCFuncPtr func) {
return 65.4;
}
Another way is to make foo
a functor
struct foo {
typedef double result_type;
template<typename FuncPtr>
double operator()(double num, FuncPtr f) const {
return 65.4;
}
};
Then you can pass foo()
to boost::bind
, and because it's templated, it will accept any linkage. It will also work with function objects, not only with function pointers.
回答2:
Try using a typedef:
extern "C" {
typedef double (*CDoubleFunc)(double);
}
double foo(double num, CDoubleFunc func) {
return 65.4;
}
来源:https://stackoverflow.com/questions/1289191/how-do-you-declare-an-extern-c-function-pointer