Stream: several bytes of data arrive from one end to the other, which is called stream
Stream class system: stream objects, and stream operators > > <<
Input / output stream
ostream class: cout,cerr,clog, istream class cin
#include<iostream>
using namespace std;
void testostream()
{
cout << "standard output " << endl; //Can redirect
cerr << "Standard error" << endl; //Cannot redirect
clog << "Standard error output" << endl;//Here you can redirect to a file
}
int main()
{
return 0;
}Many people don't know much about redirection. File redirection is that the input or output of the program can be completed by files
Input from a file into a program, or into a file in a program
#include<iostream>
#include<cstdio>
using namespace std;
void testostream()
{
cout << "standard output " << endl; //Can redirect
cerr << "Standard error" << endl; //Cannot redirect
clog << "Standard error output" << endl;//Here you can redirect to a file
}
int main()
{
int temp, temp2;
freopen("fox.txt","r",stdin);//Redirect input when the program runs, read data into the file
scanf("%d%d",&temp,&temp2);//Data will be fetched according to format control characters
cout << temp << temp2 << endl;//We print the test
freopen("Fox 2.txt", "w", stdout);//Oriented to output
printf("%d", temp+ temp2);//The print here will be output to a file
return 0;
}Processing of output character class
One is to call member functions, and the other is to call normally
#include<iostream>
#include<cstdio>
using namespace std;
void testostream()
{
cout << "standard output " << endl; //Can redirect
cerr << "Standard error" << endl; //Cannot redirect
clog << "Standard error output" << endl;//Can redirect
//Character class processing
cout.put('A');//Call member function
cout << 'A' << endl;//Normal output
char c = 'W';
cout.put(c);//Variables and constants are OK
cout << c << endl;
cout.write("I love you\n",4);//To intercept the output, this member function needs to be limited in length
//Input stream
//Character input
c = cin.get();//The return value of the get() function is our input
cout.put(c);
//String input
while (cin.get() != '\n');//Clear buffer processing
char str[20] = "";
cin.getline(str,20);
cout.write(str,20);
//Note that the processing must be processed as char * and cannot process C++ string classes
//Format control
}
int main()
{
testostream();
return 0;
}Format control characters: include header file iomanip
One is to call member functions, and the other is to use flow control characters
#include<iostream>
#include<cstdio>
#include<iomanip>
using namespace std;
void testiomanip()
{
double pi = 3.1415926535;
cout << setprecision(4);//Set stream format output.. Here is to set the number of significant digits
cout << pi << endl;
cout << fixed << setprecision(4);//The combination of fixed is the setting of effective decimal places
cout << pi << endl;
cout.precision(8);//Basically, all flow controllers correspond to a member function
cout << pi << endl;
cout << hex << 58 << endl;//hexadecimal
cout << oct << 48 << endl;//octal number system
cout << setbase(16);//Set to hexadecimal, you must enter the commonly used 8 10 16. There is no binary
cout << 58 << endl;
cout << setw(8);//Set interval / / the default is right alignment
cout << setiosflags(ios::left);//Set to left alignment
//cout << setiosflags(ios::right);// Set right alignment
cout << setw(8) << 58 << setw(8) << 68 << endl;
}
int main()
{
testiomanip();
return 0;
}
2. Character stream processing:
Character stream header file ssstream
The subclass is the character stream class for istreamstream input
The subclass is the stream class of ostreamstream for output
We generally use stream, which can be input or output
General character stream object for String segmentation String conversion problem
#include<iostream>
#include<cstdio>
#include<iomanip>
#include<sstream>
using namespace std;
void teststringstream()
{ //Building character stream objects
stringstream Fox(string("I am Fox"));//Construction mode
stringstream Foxson;
Foxson << "I love you!"; //Stream the data in
cout << Foxson.str();//Read the data in the stream
string data;
Foxson >> data;//Stream objects into data
cout << data << Foxson.str() << endl;//Does not affect the original data
//Foxson.str("");// Delete data by overwrite
//Conversion between string and number
int Num = 34567;
char input[20] = "";
stringstream tempstr(input);//Build an empty character stream object
tempstr << Num;//Stream the numbers in
tempstr >> input;//Stream out as a string
cout << input << endl;
//Data is converted according to control characters
//String to number is easier
stringstream tempstrnum("12345");
tempstrnum >> Num;
cout << Num << endl;
//String segmentation
stringstream sdata("56,78,9121,84,48,1841,10");
int numdata[7];
char cdata[6];
for (int i = 0; i < 7; i++)
{
if (i==6)//The last time there was no comma
{
sdata >> numdata[i];//data is int, which streams objects 56 as integers
}
else
{
sdata >> numdata[i];//data is int, which streams objects 56 as integers
sdata >> cdata[i];//The character flows the comma away
//Data will be retrieved according to the type of variable
}
}
for (int i = 0; i < 7; i++)
{
cout << numdata[i]<<"\t";
}
cout << endl;
//For multiple data conversion operations on the same stream, clear must be performed on the stream object
tempstr.clear();
tempstr << Num;//Stream the numbers in
tempstr >> input;//Stream out as a string
cout << input << endl; //Use clear multiple times to re-enter the data
}
int main()
{
teststringstream();
return 0;
}3. File flow
ofstream class // Output output to file, write operation
ifstream Class / / read operation
fstream class / / readable and writable
Header file: fstream
Open file: read / write mode
ios::in / / open the file by reading
ios::out / / open the file by writing. It has the function of creating, but it will overwrite the file
ios::app / / append mode
ios::atr / / open the existing file. The file points to the end of the file
ios::trunc / / create function
ios::nocreate / / does not have the function of creating
ios::norlace / / do not replace
ios::binary / / binary mode
Combination mode|
Readable and writable ios::in|ios::out
Binary readable writable ios::binary|ios::in|ios::out
true is returned if the file is opened successfully, false is returned if it fails
Close the file object. close();
Read / write mode:
Read and write by stream
Note that spaces and line breaks are ignored
#include<iostream>
#include<cstdio>
#include<iomanip>
#include<sstream>
#include<fstream>
using namespace std;
void asciiRWFile(const char *ReadFlieName,const char *WriteFlieName)
{
fstream read(ReadFlieName,ios::in);
fstream writ(WriteFlieName, ios::out);
//1. Read and write by stream
//while (1) //eof returns false if it does not end, so it is reversed
//{
// char key;
// read >> key;
// if (read.eof())//eof returns true at the end, so execute
// {
// break;
// }
// writ << key;// It can be saved directly to the file pointed to by the file object
//}
//2. The stream ignores spaces and line breaks. We read and write through member function characters
//while (1)
//{
// char key;
// read.get(key);
// if (read.eof())//eof returns true at the end, so execute
// {
// break;
// }
// writ.put(key);// Output to the specified file
//}
//Stream string read / write mode
while (!read.eof())
{
char str[1024] = "";//Initialization is required for each read
read.getline(str,1024);
writ.write(str,strlen(str));//Count the visible length and write it without line feed
writ << endl;//Flow a new line in
}
read.close();
writ.close();
}
int main()
{
asciiRWFile("Read file.txt","123.txt");
return 0;
}Binary read / write:
Binary reading and writing is much simpler than character reading and writing
#include<iostream>
#include<cstdio>
#include<iomanip>
#include<sstream>
#include<fstream>
using namespace std;
void binaryRWFile(const char* ReadFlieName, const char* WriteFlieName)
{
fstream read(ReadFlieName, ios::in|ios::binary);
fstream writ(WriteFlieName, ios::out|ios::binary);
while (!read.eof())
{
char str[1024] = "";
read.fstream::read(str, 1024);//There is a problem with the same name. Limit the class name
writ.write(str, 1024);
}
read.close();
writ.close();
}
int main()
{
binaryRWFile("Read file.txt","21323.txt");
return 0;
}File pointer positioning
ios::beg;// File start
ios::end;// end of file
ios::cur / / current location of the file
#include<iostream>
#include<cstdio>
#include<iomanip>
#include<sstream>
#include<fstream>
using namespace std;
void testSeekRead(const char* ReadFlieName)
{
fstream fread(ReadFlieName, ios::in);
fread.seekg(4);
char key = fread.get();
cout << key << endl;
fread.seekg(-4, ios::end);
key = fread.get();
cout << key << endl;
}
int main()
{
testSeekRead("Read file.txt");
return 0;
}