CPP Cin 常见I/O方法总结+合并转

cin 用法详解：https://blog.youkuaiyun.com/bravedence/article/details/77282039

cin.ignore 详解：https://blog.youkuaiyun.com/imkelt/article/details/52202002

EOF for cin: https://blog.youkuaiyun.com/foxpeter/article/details/6072130

cin.get() and EOF: https://blog.youkuaiyun.com/qq_34686440/article/details/55005165

how to use eof(): https://blog.youkuaiyun.com/kmno400/article/details/5724577

C I/O: https://blog.youkuaiyun.com/baidu_41560343/article/details/90719093

find newline: https://bbs.youkuaiyun.com/topics/50041255

CPP StringStream: https://lavi-liu.blog.youkuaiyun.com/article/details/89070296

C/CPP string数据类型转换及分隔：https://www.cnblogs.com/loveprogramme/p/11000421.html

Cpp fstream: https://blog.youkuaiyun.com/Andy710660541/article/details/51045385； https://blog.youkuaiyun.com/xunmengpiaoyun/article/details/17054849?utm_medium=distribute.pc_relevant.none-task-blog-2%7Edefault%7EBlogCommendFromMachineLearnPai2%7Edefault-1.control&dist_request_id=1328769.40256.16175124726219943&depth_1-utm_source=distribute.pc_relevant.none-task-blog-2%7Edefault%7EBlogCommendFromMachineLearnPai2%7Edefault-1.control

'\0' vs. "\0" https://bbs.youkuaiyun.com/topics/390615761

input processing:

• cin>>
  • return the input stream buffer: istream& ==> can be checked in a conditional clause ==> false if EOF/nothing to read while trying to get cin>>a ==> !!!! not checking 1/0 of the value read
  • since it returns istream& ==> we can chain it by cin>>a>>b>>.....
  • use ' ' , '\t' or '\n' as delimiter ==> cin>> read words/chunks not just 1 byte/char
  • “若缓冲区中第一个字符是空格、tab或换行这些分隔符时，cin>>会将其忽略并清除，继续读取下一个字符，若缓冲区为空，则继续等待。但是如果读取成功，字符后面的分隔符是残留在缓冲区的，cin>>不做处理。”
• cin.get
  • cin.get() returns int ==> ascii val of the char, and EOF with the value of -1 
  • cin.get(dest_char/char*, num_char, delimiter char)  returns istream& ==> we can chain it by cin.get(a).get(b)..... ===> read a single char or a specified chunk of size num_char before reaching delimiter char each time.
  • "遇到换行符时结束读取，但是不对换行符进行处理，换行符仍然残留在输入缓冲区。"
  • "cin.get(str,size);读取一行时，只能将字符串读入C风格的字符串中，即char*"
• cin.getline
  • "getline读取一行字符时，默认遇到’\n’时终止，并且将’\n’直接从输入缓冲区中删除掉，不会影响下面的输入处理。"
  • "getline函数可以将字符串读入C++风格的字符串中，即string类型。"
  • istream& getline(char* s, streamsize count, char delim);
• string::getline
  • "getline遇到结束符时，会将结束符一并读入指定的string中，再将结束符替换为空字符。" ==> similar result to cin.getline()
  • istream& getline ( istream& is, string& str, char delim);
  • the buffer for string::getline can grow dynamically by the power of cpp_string.
  • ==> if the delimitor is not found, getline will simply copy everything.
  • ==> when the istream is not valid (say only EOF), getline will not change the string at all.
• <stdio.h> gets
  • "从标准输入设备读字符串，可以无限读取，不会判断上限，以回车结束或者EOF时停止读取"
  • char *gets( char *buffer );
  • suppressed use in CPP

 

other functionals

• cin.ignore(int N, char delim) ==> ignore up to N char/bytes before encountering "delim" char
  • istream::ignore(char x) is not implemented ==> ignore(' ') will convert ' ' to an int and ignore that many char
  • ignore() ignores 1 char
  • !!! ignore (len, delim) will ignore the delim char as well !!!
    • see test code

    • #include <iostream>
      #include <sstream>
      #include <string>
      
      using namespace std;
      
      int main()
      {
      	string s = "1234567,67653562,25346457,324234\n";
      	istringstream ss;
      	ss.str(s);
      	ss.ignore(100, ',');
      	getline(ss, s, ',');
      	cout << s << endl;
      	ss.ignore(100, ',');
      	ss.ignore();
      	getline(ss,s,',');
      	cout << s;
      
      	cin.ignore(100, ','); //ignore(len, delimiter) ignores the delimiter char.!!!!
      	cin >> s;
      	cout << s;
      	return 0;
      }

       

• cin.eof() ==> return the value of eofbit ==> set to 1 when encountering a "proper" EOF 

examples for string::getline and istream::ignore()

#include <iostream>
#include <string>
#include <sstream>

using namespace std;

int main()
{
	string t1 = "res";
	string t2 = "res board";
	istringstream ss;

	string s1, s2;
	s1 = s2 = "temp";
	ss.str(t1);
	
	getline(ss, s1, ' ');
	cout << "string::getline(stream, string, delim) will copy everything is delim is not found.\n";
	cout << s1 << endl;
	getline(ss, s2);
	cout << "when the stream is invalid (with only EOF), string::getline will not change the string.\n";
	cout << (s2 == "") << " the string is not set to \"\"." << endl;
	cout << "the string still is: \n";
	cout << s2 << endl;

	ss.clear();
	ss.str(t2);
	ss.ignore(' ');
	getline(ss, s1);
	cout << s1 << endl;

	return 0;
}

s1 is not changed, since ss is empty