C++ input and output and txt file input example

std::istream

typedef basic_istream<char> istream;

An input stream object can read and interpret input from character sequences. Specific members are provided to perform these input operations (see functions below).

A standard object cinis an object of this type.

std::istream::getline

istream& getline (char* s, streamsize n );
istream& getline (char* s, streamsize n, char delim );

Extracts characters from the stream as unformatted input and stores them as ca string sinto until the extracted characters are delimiting characters, nor characters have been written s(including the terminating null character).

// istream::getline example
#include <iostream>     // std::cin, std::cout

int main () {
    
    
  char name[256], title[256];

  std::cout << "Please, enter your name: ";
  std::cin.getline (name,256);

  std::cout << "Please, enter your favourite movie: ";
  std::cin.getline (title,256);

  std::cout << name << "'s favourite movie is " << title;

  return 0;
}

Please, enter your name: sjn
Please, enter your favourite movie: op
sjn's favourite movie is op

This example shows how to cinget lines from the standard input stream ( )

std::ostream

typedef basic_ostream<char> ostream;

Output stream objects can write sequences of characters and represent other types of data. Specific members are provided to perform these output operations (see functions below).

Standard objects cout, cerrand clogare objects of this type.

std::ostream::operator<<

arithmetic types (1)	
ostream& operator<< (bool val);
ostream& operator<< (short val);
ostream& operator<< (unsigned short val);
ostream& operator<< (int val);
ostream& operator<< (unsigned int val);
ostream& operator<< (long val);
ostream& operator<< (unsigned long val);
ostream& operator<< (float val);
ostream& operator<< (double val);
ostream& operator<< (long double val);
ostream& operator<< (void* val);
stream buffers (2)	
ostream& operator<< (streambuf* sb );
manipulators (3)	
ostream& operator<< (ostream& (*pf)(ostream&));
ostream& operator<< (ios& (*pf)(ios&));
ostream& operator<< (ios_base& (*pf)(ios_base&));

// example on insertion
#include <iostream>     // std::cout, std::right, std::endl
#include <iomanip>      // std::setw

int main() {
    
    
	int val = 65;

	std::cout << std::right;       // right-adjusted (manipulator)
	std::cout << std::setw(10);    // set width (extended manipulator)

	std::cout << val << std::endl; // multiple insertions

	return 0;
}

output

        65

C++ reads txt files

#include <iostream>
#include <vector>
#include <string>
#include <sstream>
#include <fstream>
#include <cassert>

using namespace std;

void txt_to_vectordouble(vector<float>& res, string pathname)
{
    
    
	ifstream infile;
	infile.open(pathname.data());   //将文件流对象与文件连接起来 
	assert(infile.is_open());       //若失败,则输出错误消息,并终止程序运行 
	string s;
	while (getline(infile, s)) {
    
    
		istringstream is(s);        //将读出的一行转成数据流进行操作
		double d;
		while (!is.eof()) {
    
    
			is >> d;
			res.push_back(d);
		}
		s.clear();
	}
	infile.close();                 //关闭文件输入流 
}

int main()
{
    
    
	vector<float> data;
	txt_to_vectordouble(data, "./1.txt");
	for (auto a : data) {
    
    
		cout << a << endl;
	}

	return 0;
}