C ++ _ note_10_io

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11. I

c ++ io of three parts: a keyboard, a file, memory, are referred to a standard i / o, the file i / o, serial i / o.

11.1 Standard io

11.1.1 standard input stream

#include<iostream>
using namespace std;

int main(int argc, char *argv[])
{
	int a;
	float b;
	char s[10];
	cin>>a;
	cin>>b;
	cin>>s; //不能接收空格
	
	cout<<a<<endl;
	cout<<b<<endl;
	cout<<s<<endl;
	cin.get();
	return 0;
}

/*
1
1.2
a b
1
1.2
a
*/

Exists between the input buffer and the Keyboard, exists between the output buffer and a screen.

When the input buffer if no data will be blocked.

#include<iostream>
using namespace std;

int main(int argc, char *argv[])
{
	char c;
	while( (c = cin.get()) != EOF)
	{
		cout<<c<<endl;
	}
	cin.get();
	return 0;
}

/*
aa	//此时已经输入input buf
a
a


^Z
请按任意键继续. . .
*/

cin.get ():

• istream& get (char& c);
• istream& get (char* s, streamsize n);
• istream& get (char* s, streamsize n, char delim);
• istream& get (streambuf& sb);
• istream& get (streambuf& sb, char delim);

#include<iostream>
using namespace std;

int main(int argc, char *argv[])
{
	char a,b,c;
	cin.get(a);
	cin.get(b);
	cin.get(c);
	
	cout<<a<<b<<c<<"there is data in buf.\n";
	
	cin.get(a).get(b).get(c);
	cout<<a<<b<<c<<endl;
	
	cin.get();
	return 0;
}
/*
abcdefg
abcthere is data in buf.
def
*/

The input string containing spaces by getline():

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

#include<iostream>
using namespace std;

int main(int argc, char *argv[])
{
	char s[10];
	cin.getline(s,10);
	cout<<s<<endl;
	
	cin.get();
	return 0;
}

/*
aaaaa sssss dd
aaaaa sss
*/

The following are three non-common functions:

• istream& ignore (streamsize n = 1, int delim = EOF);，ignore until delim
• int peek(); Detect whether there is a data buffer
• istream& putback (char c); The return buffer c

#include<iostream>
using namespace std;
int main(int argc, char *argv[])
{
	char buf1[10],buf2[10];
	int ret;
	cin>>buf1;
	cin.ignore(1);
	ret = cin.peek();
	cout<<"ret:"<<ret<<endl;
	
	cin>>buf2;
	cout<<"buf1:"<<buf1<<endl;
	cout<<"buf2:"<<buf2<<endl;
	
	cin.get();
	return 0;
}

/*
aa  bb
ret:32
buf1:aa
buf2:bb
*/

The following is the official website given putback()example.

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

int main () {
  std::cout << "Please, enter a number or a word: ";
  char c = std::cin.get();

  if ( (c >= '0') && (c <= '9') )
  {
    int n;
    std::cin.putback (c);
    std::cin >> n;
    std::cout << "You entered a number: " << n << '\n';
  }
  else
  {
    std::string str;
    std::cin.putback (c);
    getline (std::cin,str);
    std::cout << "You entered a word: " << str << '\n';
  }
  return 0;
}

11.1.2 Standard Output

Definition standard output stream:extern ostream cout;

Common functions:

• ostream& flush(); So that information immediately forced output buffer.
• ostream& put (char c);，cout.put('a').put('b');
• ostream& write (const char* s, streamsize n);, The output binary stream.
• streamsize width();
• char fill();
• fmtflags setf();

char *p = "hello";
cout.write(p,5)<<endl;

#include<iostream>
using namespace std;
#include <iomanip>
int main(int argc, char *argv[])
{
   cout<<"<start>"
   	<<setw(30)
   	<<setfill('*')
   	<<setiosflags(ios::showbase)
   	<<hex
   	<<100
   	<<"<end>"
   	<<endl;
   cout<<endl;
   cout.width(5);
   cout.fill('*');
   cout.setf(ios::showbase);
   cout.setf(ios::internal);
   cout<<hex<<100<<endl;
   
   cin.get();
   return 0;
}

/*
<start>**************************0x64<end>

0x*64
*/

11.2 file io

open a file:void open (const char* filename, ios_base::openmode mode = ios_base::out);

Call to bool is_open() const;determine whether the open was successful.

Read and write functions:

• ostream& write (const char* s, streamsize n);
• istream& read (char* s, streamsize n);

Entry

std::ifstream ifs;
ifs.open ("test.txt", std::ifstream::in);

char c = ifs.get();
while (ifs.good()) {
    std::cout << c;
    c = ifs.get();
}

ifs.close();

member constant	stands for	access
in *	input	File open for reading: the internal stream buffer supports input operations.
out	output	File open for writing: the internal stream buffer supports output operations.
binary	binary	Operations are performed in binary mode rather than text.
ate	at end	The output position starts at the end of the file.
app	append	All output operations happen at the end of the file, appending to its existing contents.
trunc	truncate	Any contents that existed in the file before it is open are discarded.

Export

std::ofstream ofs;
ofs.open ("test.txt", std::ofstream::out | std::ofstream::app);
ofs << " more lorem ipsum";
ofs.close();
//or
//std::ofstream fout("test.txt");

Notice that outway, if the file exists, then clear the contents.

member constant	stands for	access
in	input	File open for reading: the internal stream buffer supports input operations.
out *	output	File open for writing: the internal stream buffer supports output operations.
binary	binary	Operations are performed in binary mode rather than text.
ate	at end	At The the Output position Soho starts at The AT at The End of File. File does not exist error
app	append	All output operations happen at the end of the file, appending to its existing contents.
trunc	truncate	Any contents that existed in the file before it is open are discarded.