C++ I/O streams have internal buffers. C = cine.get (void) reads one character at a time and leaves the newline generated by the Enter key in the input queue

#include<iostream>

using namespace std;

int main(a) {
    char c;
    int i = 0;
    do {
        c = cin.get(a); cout << ++i <<":" <<
            static_cast<int>(c) << endl;
    } while(c ! ='q');
    return 0;

}
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2. Cin. Get () does not work because there are newline characters left in the buffer after cin

#include <iostream>

int main(a)
{
	// Get the buffer pointer to the cin object

	auto p = std::cin.rdbuf(a);// Read characters from keyboard into buffer, leaving all characters in buffer

	auto x = std::cin.peek(a); std::cout <<"x= " << x << std::endl;
	// Displays the number of characters in the buffer
	// Save the initial value because the value returned by each read is different
	auto count = p->in_avail(a); std::cout <<"There are " << count << "characters in the buffer." << std::endl;
	// Remove all the characters from the buffer and display them
	for (int i = 0; i < count; i++)
	{
		std::cout << i + 1 << ":" << std::cin.get() << std::endl;
	}

	std::cin.get(a);return 0;
}
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Ofstrem writes data to text files.

The flow of output data:



If the file already exists, delete the file directly.

Writing Data to a File — Auto Type Recognition

In the software debugging technology, a very important technology is to write some information in the software running process to the “log file”. But the information should also be displayed on the screen so that programmers can view it in real time. The simplest way is this:

std::ofstream output("debug.log", ios::out);
output << __FILE__ << ":" << __LINE__ << "\t" << "Variable x = " << x;
cout << __FILE__ << ":" << __LINE__ << "\t" << "Variable x = " << x;
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Let’s use Streambuf to construct a class of its own to do this

#include <streambuf>
#include <iostream>
#include <fstream>

// The Linux tee command is used to read the standard input data and output its contents to a file.
// The tee instruction reads data from the standard input device, outputs its contents to the standard output device, and saves it as a file.
class teebuf : public std::streambuf
{
public:
    // Construct a streambuf which tees output to both input
    // streambufs.
    teebuf(std::streambuf* sb1, std::streambuf* sb2)
        : sb1(sb1)
        , sb2(sb2)
    {
    }
private:
    // This tee buffer has no buffer. So every character "overflows"
    // and can be put directly into the teed buffers.
    virtual int overflow(int c)
    {
        if (c == EOF)
        {
            return! EOF; }else
        {
            int const r1 = sb1->sputc(c);
            int const r2 = sb2->sputc(c);
            returnr1 == EOF || r2 == EOF ? EOF : c; }}// Sync both teed buffers.
    virtual int sync(a)
    {
        int const r1 = sb1->pubsync(a);int const r2 = sb2->pubsync(a);return r1 == 0 && r2 == 0 ? 0 : - 1;
    }
private:
    std::streambuf* sb1;
    std::streambuf* sb2;
};

class teestream : public std::ostream
{
public:
    // Construct an ostream which tees output to the supplied
    // ostreams.
    teestream(std::ostream& o1, std::ostream& o2);
private:
    teebuf tbuf;
};

teestream::teestream(std::ostream& o1, std::ostream& o2)
    : std::ostream(&tbuf)
    , tbuf(o1.rdbuf(), o2.rdbuf() {}int main(a)
{
    std::ofstream output("debug.log");
    // create file/screen output stream object tee
    teestream tee(std::cout, output);

    auto x = 1.1;
    tee << __FILE__ << ":" << __LINE__ << "\t" << "Variable x = " << x;

    return 0;
}
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Effect:

Possible error:

1. The file does not exist when the file is read. 2

Check whether the file is opened correctly:

2. Fail () returns true, the file is not open

ofstream output("scores.txt");
if (output.fail())  {
    cout << R"(Can't open file "scores.txt"!) ";
  }
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Create file input stream, open file score.txt, read data from file with >> 3, use fail() function to check whether file is open 4, put read statement into loop, use eof() as loop condition 5, close file

//std::c++latest
#include <fstream>
#include <iostream>
#include <filesystem>
#include <string>
using std::ifstream;
using std::ofstream;
using std::cout;
using std::endl;
using std::string;
namespace fs = std::filesystem;

int main(a)
{
	// The first step is to associate the file

	fs::path p{ "scores.txt" };

	// Create a stream input object
	ifstream input{ p };

	// The third step is to use fail to determine whether the stream is open properly
	if (input.fail())
	{
		cout << "Can't open file " << p << endl;
		std::cin.get(a);return 0;
	}
	// Step 4, define some variables to store the data
	string name{ "" };
	double score{ 0.0 };

	// Read the name and score from the file
	//input >> name >> score;
	//cout << name << " " << score << endl;
	//input >> name >> score;
	//cout << name << " " << score << endl;
	
	while (input.eof() = =false)
	{
		cout << static_cast<char>(input.get());
	}

	std::cin.get(a);return 0;
}
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