forstream的“预期不合格身份”

Question

I wrote the following C++ program, but at the line where I used out_stream.open() , it keeps telling me that there are errors about "unknown typename 'out_stream'" and "Expected unqualified-id".

I am new to C++ and I think I just copied down the lines from my textbook, so I can't figure out where it's wrong. Please bear with me if it is a really simple mistake.

Here's my code:

#include <iostream>
#include <fstream>
#include <cmath>
#include <vector>
#include <boost/random.hpp>
#include <boost/random/mersenne_twister.hpp>
#include <boost/random/normal_distribution.hpp>
#include <boost/random/uniform_int_distribution.hpp>
#include <boost/math/distributions.hpp>


std::ofstream out_stream;
out_stream.open("output.txt");


int main()
{
    std::cout<<"hello world!";
    return 0;

}

Answer 1

You cannot to this

out_stream.open("output.txt");

outside of a function. Put it inside the main().

int main()
{
    out_stream.open("output.txt");
    std::cout<<"hello world!";
    return 0;

}