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Defined in header <functional> | ||
template<class Res,class T> std::mem_fun_t<Res,T> mem_fun( Res(T::*f)()); | (1) | (deprecated in C++11) (removed in C++17) |
template<class Res,class T> std::const_mem_fun_t<Res,T> mem_fun( Res(T::*f)()const); | (1) | (deprecated in C++11) (removed in C++17) |
template<class Res,class T,class Arg> std::mem_fun1_t<Res,T,Arg> mem_fun( Res(T::*f)(Arg)); | (2) | (deprecated in C++11) (removed in C++17) |
template<class Res,class T,class Arg> std::const_mem_fun1_t<Res,T,Arg> mem_fun( Res(T::*f)(Arg)const); | (2) | (deprecated in C++11) (removed in C++17) |
Creates a member function wrapper object, deducing the target type from the template arguments. The wrapper object expects a pointer to an object of typeT as the first parameter to itsoperator().
This function and the related types were deprecated in C++11 and removed in C++17 in favor of the more generalstd::mem_fn andstd::bind, both of which create callable adaptor-compatible function objects from member functions.
Contents |
| f | - | pointer to a member function to create a wrapper for |
A function object wrappingf.
May throw implementation-defined exceptions.
The difference betweenstd::mem_fun andstd::mem_fun_ref is that the former produces a function wrapper that expects a pointer to an object, whereas the latter — a reference.
Demonstratesstd::mem_fun usage and compares it withstd::mem_fn. C++11/14 compatible compilation mode might be necessary: g++/clang++ with -std=c++11, cl with /std:c++11, etc. On recent compilers, e.g. gcc-12, might issue "deprecated declaration" warnings if not compiled in C++98 mode.
#include <functional>#include <iostream> struct S{int get_data()const{return data;}void no_args()const{std::cout<<"void S::no_args() const\n";}void one_arg(int){std::cout<<"void S::one_arg()\n";}void two_args(int,int){std::cout<<"void S::two_args(int, int)\n";}#if __cplusplus > 201100int data{42};#elseint data; S(): data(42){}#endif}; int main(){ S s; std::const_mem_fun_t<int, S> p= std::mem_fun(&S::get_data);std::cout<<"s.get_data(): "<< p(&s)<<'\n'; std::const_mem_fun_t<void, S> p0= std::mem_fun(&S::no_args); p0(&s); std::mem_fun1_t<void, S,int> p1= std::mem_fun(&S::one_arg); p1(&s,1); #if __cplusplus > 201100// auto p2 = std::mem_fun(&S::two_args); // Error: mem_fun supports only member functions// without parameters or with only one parameter.// Thus, std::mem_fn is a better alternative:auto p2=std::mem_fn(&S::two_args); p2(s,1,2); // auto pd = std::mem_fun(&S::data); // Error: pointers to data members are not supported.// Use std::mem_fn instead:auto pd=std::mem_fn(&S::data);std::cout<<"s.data = "<< pd(s)<<'\n';#endif}
Possible output:
s.get_data(): 42void S::no_args() constvoid S::one_arg(int)void S::two_args(int, int)s.data = 42
(C++11) | creates a function object out of a pointer to a member (function template)[edit] |
(deprecated in C++11)(removed in C++17) | creates a wrapper from a pointer to member function, callable with a reference to object (function template)[edit] |
