Question

Like this function in C:

size_t fwrite ( const void * ptr, size_t size, size_t count, FILE * stream );

I’ve looked in C++ file stream and found this one:

ostream& write ( const char* s , streamsize n );

this one only accepts char* instead of void*

but does it really matter if I use a C-style fwrite function in c++?

Answer 1

Streams are probably what you’re looking for unless I misunderstand your question. There are many flavors that handle different jobs, like outputting to a file:

#include <cstdlib>
#include <fstream>
#include <string>
using namespace std;


int main()
{
    ofstream f("c:\\out.txt");

    const char foo[] = "foo";
    string bar = "bar";
    int answer = 42;

    f << foo << bar<< answer;

    return 0;
}

…building strings like you would with printf:

#include <cstdlib>
#include <sstream>
#include <string>
#include <iostream>
using namespace std;


int main()
{
    stringstream ss;

    const char foo[] = "foo";
    string bar = "bar";
    int answer = 42;

    ss << foo << bar<< answer;
    string my_out = ss.str();

    return 0;
}

…and they can even handle your own types, if you tell them how:

#include <cstdlib>
#include <string>
#include <iostream>
using namespace std;

class MyGizmo
{
public:
    string bar_;
    int answer_;

    MyGizmo() : bar_("my_bar"), answer_(43) {};
};

ostream& operator<<(ostream& os, const MyGizmo& g)
{
    os << g.bar_ << " = " << g.answer_;
    return os;
}
int main()
{
    MyGizmo gizmo;
    cout << gizmo;

    return 0;
}