what is wrong with this program?

Question

#include 
#include 
#include 

using namespace std;

int main() {
    string x;
    getline(cin,x);
    ofstream o(\"f:/demo         


        

Answer 1

You are treating an std::string like something that it is not. It's a complex object that, somewhere in its internals, stores characters for you.

There is no reason to assume that a character array is at the start of the object (&x), and the sizeof the object has no relation to how many characters it may indirectly hold/represent.

You're probably looking for:

o.write(x.c_str(), x.length());

Or just use the built-in formatted I/O mechanism:

o << x;

Answer 2

You get exactly what you write: the binary raw value of a pointer to char...

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

int main()
{
    string x;
    getline(cin,x);
    ofstream o("tester.txt");
    o << x;
    o.close();
}

If you insist on writing a buffer directly, you can use

o.write(x.c_str(), x.size());

PS A little attention to code formatting unclouds the mind

Answer 3

You seem to have an incorrect model of sizeof, so let me try to get it right.

For any given object x of type T, the expression sizeof(x) is a compile-time constant. C++ will never actually inspect the object x at runtime. The compiler knows that x is of type T, so you can imagine it silently transforming sizeof(x) to sizeof(T), if you will.

#include <string>

int main()
{
    std::string a = "hello";
    std::string b = "Stack Overflow is for professional and enthusiast programmers, people who write code because they love it.";
    std::cout << sizeof(a) << std::endl;   // this prints 4 on my system
    std::cout << sizeof(b) << std::endl;   // this also prints 4 on my system
}

All C++ objects of the same type take up the exact amount of memory. Of course, since strings have vastly different lengths, they will internally store a pointer to a heap-allocated block of memory. But this does not concern sizeof. It couldn't, because as I said, sizeof operates at compile-time.

Answer 4

You're passing the object's address to write into the file, whereas the original content lies somewhere else, pointed to by one of its internal pointers.

Try this:

string x;
getline(cin,x);
ofstream o("D:/tester.txt");
o << x;
// or
// o.write( x.c_str() , x.length());