cpp pointer for function write on binary file [duplicate]

Question

I tried to create function that get pointer for the functions of binary file, write and read. Both of functions need get :

1)char* (on write function the char* mean from witch address write, and on read function char* mean , to witch address read)

2) int (on write address that meam how many wirte and on read function that mean how many read).

I want create function that get pointer for read/ write , but i get an error my code.

#include <iostream>
using namespace std;
#include <fstream>

void func(void(*funcToCall)(char*, int))
{
    char * temp= "zzz";
    funcToCall(temp, 3);
}
int main()
{
    fstream dskfl;
    dskfl.open("aa.txt", ios::out |  ios::binary);
    dskfl.close();
    dskfl.open("aa.txt", ios::out | ios::in | ios::binary);

    char ddd[]= "fffff";
    dskfl.write((char*)ddd, 5);
    dskfl.seekp(0);

    func(dskfl.write);
    dskfl.close();
}

i get error on line

func(dskfl.write);

Error   1   error C3867: 'std::basic_ostream<char,std::char_traits<char>>::write': function call missing argument list; use '&std::basic_ostream<char,std::char_traits<char>>::write' to create a pointer to member

why please?

You need two pieces of information to call a method of a class - instance of the class and the method to call. fstream* instance = &dskfl; and void (fstream::*method)(char*, int) = &fstream::write; and then use (instance->*method)(char*, int) to call the method. — Vishal
– Vishal, Commented Mar 16, 2016 at 7:06
@Vishal i changed to "void func(fstream* instance, void(fstream::*method)(char*, int) )" and call of function like func(&dskfl,&( fstream::write)); i get error 4 IntelliSense: argument of type "std::basic_ostream<char, std::char_traits<char>> &(std::basic_ostream<char, std::char_traits<char>>::*)(const char _Str, std::streamsize _Count)" is incompatible with parameter of type "void (std::basic_fstream<char, std::char_traits<char>>::)(char *, int)" — jordan
– jordan, Commented Mar 16, 2016 at 7:21

nikniknik2016 · Accepted Answer · 2016-03-16 07:03:52Z

0

you can use a lambda

for example:

change the signature of your outer func for receive a std::function:

void func(std::function<void(char*, int)>&& funcToCall)

and call it like this:

func([&dskfl](char* c, int i){ dskfl.write(c, i); });

answered Mar 16, 2016 at 7:03

nikniknik2016

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