File input and output problems

firegun

The above examples are selected from Chapter 13 Section 10 of the C++ Standard Library. The main floor has a comprehensive understanding of the relationship between stream and streambuf. You can read this book

fcuptfwfn

But some books say that fstream fio; is to create an input and output file stream object, that is, you can use this object for input and output operations~~~~? Don't understand—_—!

nimasile1

Use fstream like this

#include <iostream>
#include <fstream>
using namespace std;
int main()
{
    fstream myfile;
    myfile.open("a.txt",ios::out|ios::app);
    if(!myfile)
    {
        cout<<"File error!"<<endl;
        system("pause");
        exit(1);
    }
    myfile<<"new add "<<endl<<"URL;
    myfile.close(); //Pay attention to close
  
    myfile.open("a.txt",ios::in);
    if(!myfile)
    {
        cout<<"File reading error!"<<endl;
        system("pause");
        exit(1);
    }
    char ch;
    while(myfile.get(ch))
    {
        cout.put(ch);
    }
    myfile.close();
    system("pause");
}

nimasile1

Your question is the same as the example I gave

Remember to close the pointer after adding

liebersie

Is the file pointer operation problem:
#include<iostream>
//#include<conio.h>
#include<fstream>
using namespace std;

int main()
{
        fstream file("a.txt",ios::in|ios::out);
        string s1,s2;

        s1="abcd 1234\n";
        file<<s1; //Write characters into the file, and the file pointer also points to the end of the file
        file.seekg(ios_base::beg);//Move the file pointer back to the head of the file
        file>>s2;
        cout<<"s2="<<s2<<endl;//s2 is empty

        file.close();
        //getch();
        return 0;
}

The output is:
s2=abcd //Because the read is not read by line, it is distinguished by spaces

fcuptfwfn

Thanks:fangjiehong,firegun,nimasile1
I understand all the programs you wrote, but the program I wrote (the one that only defines the fstream stream) compiles and runs without error, but it just can’t output s2 (a.txt was not created at all), so write it with you I have done a comparison of the programs or I don’t know why the a.txt text is not created? Can you analyze it for me? Thank you~~~~~

The program ofnimasile1uses an open() when writing text, and close() after writing. When reading variables, another open and then close(). Although the purpose is achieved, if you want to read and write repeatedly in a loop , I don’t feel very good.

The program offiregunis very good, but he didn't use ifstream, it used filebuf, ostream and istream.

The program ofliebersieis almost the same as mine, but after I run it, I still don’t get the s2 result (the output is empty and the text is not created). It should not be related to the compiler, right?

liebersie

Is it exactly the same? Although only one line is missing, the effect is different.
I compile with g++ under Linux and compile with VS under Windows.