Reference article:
C + + rookie tutorial notes 1
C + + rookie tutorial notes 5
What are the standard pan space characters in C/C + +?
C + + read file input stream read space line feed
C + + file stream stop about reading spaces
Detailed explanation of the use of C + + get() function
Difference between newline endl and \ n in C + +
Input and output processing in c/c + + is read by separator (line feed, comma, space, etc.)

!!! If you don't write well, please ask the boss for advice

#1. A blank line break is encountered

#include <iostream>
#include <fstream>
#include <string.h>
int main(void)
{
  std::fstream fs;
  fs.open("E:\\CodeField\\Code_Cpp\\C_Single\\csdn\\20211010\\src\\afile.dat", std::ios::trunc | std::ios::out);
  if (!fs)
  {
    std::cout << "open afile.dat err!" << std::endl;
    exit(-1);
  }
  char str[100];

  std::cout << "enter sentence 1 : ";
  std::cin >> str;
  fs << str;

  std::cout << "enter sentence 2 : ";
  std::cin >> str;
  
  // fs << str << std::endl; // => '\n' + end
  // fs << str << '\n';
  fs << str << '\t';
  // fs << str << '\v';
  // fs << str << '\f';
  // fs << str << '\r';
  // fs << str << ' ';

  std::cout << "enter sentence 3 : ";
  std::cin >> str;
  fs << str;

  fs.close();

  // Read the file a and copy it to b
  std::ifstream ifs;
  ifs.open("E:\\CodeField\\Code_Cpp\\C_Single\\csdn\\20211010\\src\\afile.dat");
  if (!ifs)
  {
    std::cout << "open afile.dat err!" << std::endl;
    exit(-1);
  }
  std::ofstream ofs;
  ofs.open("E:\\CodeField\\Code_Cpp\\C_Single\\csdn\\20211010\\src\\bfile.dat", std::ios::trunc);
  if (!ofs)
  {
    std::cout << "open bfile.dat err!" << std::endl;
    exit(-1);
  }
  int i = 0;
  while (ifs >> str)
  {
    std::cout << "chunk" << ++i << " : " << str << std::endl;
    ofs << str;
  }

  ifs.close();
  ofs.close();

  printf("--------------end--------------\n");
  return 0;
}

Output results:

enter sentence 1 : 12
enter sentence 2 : 23
enter sentence 3 : 34
chunk1 : 1223
chunk2 : 34
--------------end--------------

The file input stream was found to be stopped by a blank character ('\ t') and skipped. I don't want to skip

Contents of file afile.dat

1122 33

Contents of file bfile.dat

112233

The generated copied file (bfile.dat) is different, and the tab is missing

#2. Cancel the default ignore whitespace character of the output stream

The blank character is ignored by default. IFS > > str my understanding is to extract the file stream in front of the blank character into the variable str, and then locate the file position pointer to the blank character by default, so as to realize the function of skipping the blank character, and there will be self increment in the while loop statement.

This method can cancel the default ignore whitespace character of the output stream

void std::ios_base::unsetf(std::ios_base::fmtflags __mask)

int i = 0;
ifs.unsetf(std::ios::skipws); // Cancel default ignore whitespace

while (ifs >> str)
{

  std::cout << "chunk" << ++i << " : " << str << std::endl;
  ofs << str;
}

Output results:

enter sentence 1 : 12
enter sentence 2 : 23
enter sentence 3 : 34
chunk1 : 1223
--------------end--------------

When chunk1 was found, the cycle stopped

#3. get() method takes characters

If it is cancelled, the self increment of the while loop statement will disappear. Find an alternative, get method.

int std::istream::get()

std::istream &std::istream::get(char &__c)

Three parameters are not listed

Next, use the get() method

int i = 0;
ifs.unsetf(std::ios::skipws); // Cancel default ignore whitespace
while (ifs >> str)
{
  ifs.get();// Read a character from the ifs file input stream

  std::cout << "chunk" << ++i << " : " << str << std::endl;
  ofs << str;
}

Execution results:

enter sentence 1 : 12
enter sentence 2 : 23
enter sentence 3 : 34
chunk1 : 1223
chunk2 : 34
--------------end--------------

#4. Fetch and save blank character

While (IFS > > STR) is a loop condition. I don't understand it very well. I put it in the loop body

int i = 0;
char ch = '\0';
ifs.unsetf(std::ios::skipws); // Cancel default ignore whitespace
while (1)
{
  ch = ifs.get(); // This function changes the file position pointer??
  if (ch == EOF)
  {
    std::cout << "read file is over!" << std::endl;
    break;
  }
  else if (ch == '\n' || ch == '\t' || ch == '\v' || ch == '\f' || ch == 'r' || ch == ' ')
  {
    std::cout << "it is a white-space character !!!" << std::endl;

    std::cout << "chunk" << ++i << " : " << ch << std::endl;
    ofs << ch;// Save white space characters
  }
  else
  {
    ifs.seekg(-1, std::ios::cur); // Ordinary characters are returned. There will be problems with Chinese characters
    std::cout << "ch : " << ch << std::endl;

    ifs >> str;// Put this inside!!!
    std::cout << "chunk" << ++i << " : " << str << std::endl;
    ofs << str;
  }
}

Operation results:

enter sentence 1 : 12
enter sentence 2 : 23
enter sentence 3 : 34
ch : 1
chunk1 : 1223
it is a white-space character !!!
chunk2 :
ch : 3
chunk3 : 34
read file is over!
--------------end--------------

afile.dat

1223 34

bfile.dat

1223 34

Tab copy found

doubt

1. While (IFS > > STR), IFS > > STR what does this condition mean# Why does the loop stop when it is executed once in place 2
2. Does ifs.get() fetch a character from the stream change the file position pointer?

stay

1. std::fstream to be tested
2. getline use
3. Chinese text file reading and writing
4. Regular white space character matching