cin相关函数

basic_istream::basic_istream
basic_istream::gcount
basic_istream::get
basic_istream::getline
basic_istream::ignore
basic_istream::peek
basic_istream::putback
basic_istream::read
basic_istream::_Read_s
basic_istream::readsome
basic_istream::_Readsome_s
basic_istream::seekg
basic_istream::sentry
basic_istream::sync
basic_istream::tellg
basic_istream::unget


-----------------------------------------------------------------------------------------------------------------get（）
cin.get( &c[0],5);输入4个字符，遇到第五个字符时停止
此时：cin.gcount（）的值也为4
get函数还有：
cin.get(ch);
cin.get(c,7,'A');获取6个字符，如在此六个字符中有A的话，停止，A不获取，仍在流中
----------------------------------------------------------------------------------------------------------------getline(c,7,‘A’)
从输入流中获得6字符，或在此6个字符中有A的话，遇到A 就停止，把A删除
---------------------------------------------------------------------------------------------------------------cin.ignore( 5, 'c');输如一字符串如在前五个字符中有‘c’则去掉c前字符串（包括c），如没有则去掉前五个字符

// basic_istream_ignore.cpp

// compile with: /EHsc

#include <iostream>

int main( )

{

using namespace std;

char chararray[100];

cout<< "Type 'abcdef': ";

cin.ignore( 5, 'c' );

cin>> chararray;

cout<< chararray;

}

Type 'abcdef': abcedddsafasd

edddsafasd请按任意键继续. . .
---------------------------------------------------------------------------------------------------------cin.peek( ) 输出字符串第一个字符
// basic_istream_peek.cpp

// compile with: /EHsc

#include <iostream>

using namespace std;
int main( )

{

char c[10], c2;

cout<< "Type 'abcde': ";
c2 = cin.peek();//必须放在前面

cin.getline( c, 9 );
cout<< c2<< " "<< c <<endl;

}
Type 'abcde': afdsfdf

a afdsfdf

请按任意键继续. . .
-------------------------------------------------------------------------------------------------------cin.putback（ch）将字符ch送回字符流中

// basic_istream_putback.cpp

// compile with: /EHsc

#include <iostream>

using namespace std;
int main( )

{

char c[10], c2;
c2 = cin.get();



cin.putback( c2 );

cin.getline(&c[0], 9 );

cout<<c2<<endl;//虽然字符被返回了，这里的字符还是能输出的

cout<< c <<endl;

}
asfsdf

a

asfsdf

请按任意键继续. . .
---------------------------------------------------------------------------------------------------------------cin.read(c, count);从字符串流中读取count个字符到c数组中
// basic_istream_read.cpp

// compile with: /EHsc

#include <iostream>

using namespace std;
int main()

{

charc[10];

int count =3;
cout << "Type 'abcde': ";

// cin.get(c,10);

cin.read(c,count);



c[count] = 0;//以此作为字符串结束符，没有的话，输出会有异
cout << c<< endl;

cout<< c[count+1]<< endl;//此时c[count+1]是没有字符的

}
Type 'abcde': asfsdfsdfd

asf //说明数组中字符串为asf0
请按任意键继续. . .

当cin.read(c,count);换为cin.get（c，10）时，
Type 'abcde': afdsfasfdf

afd

f //说明数组中字符串为afd0fasfdf

请按任意键继续. . .
----------------------------------------------------------------------------------------------------------------file.seekg( 2);当刚打开文件时，指针默认指向第一个字符，2代表移动两个字符，（此时指向第三个）
file.seekg( 2, ios_base::beg);强制指针指向第一个字符，。。。。。。。也有
file.seekg( 2, ios_base::end)强制指针指向字符串的结尾，最后一字符的后一位
#include<iostream>

#include <fstream>
int main ( )

{

using namespace std;

ifstream file;

char c, c1;
file.open("c:\\basic_istream_seekg.txt" );

file.seekg(2); // chars toskip

file>> c;

cout<< c <<endl;
file.seekg( 0,ios_base::beg );

file>> c;

cout<< c <<endl;
file.seekg( -1,ios_base::end );

file>> c1;

cout<< c1<< endl;

}
2

0

9

Press any key to continue
--------------------------------------------------------------------------------------------------------------------streamoff i；i=file.tellg();返回的是文件内指针，整形

// basic_istream_tellg.cpp
// compile with: /EHsc
#include <iostream>
#include <fstream>

int main()
{
    using namespace std;
    ifstream file;
    char c;
    streamoff i;

    file.open("basic_istream_tellg.txt");
    i = file.tellg();
    file >> c;
    cout << c << " " << i << endl;

    i = file.tellg();
    file >> c;
    cout << c << " " << i << endl;
}

------------------------------------------------------------------

cin.unget();将最近获取的一个字符返回到流中

#include <iostream>

using namespace std;

int main( ) 

{

    char c[10], c2,c1;

    

    cout << "Type 'abc': ";

    c1 = cin.get( );

    c2 = cin.get( );

    cin.unget( );

    cin.getline( c, 9 );

    cout << "the c1 is "<<c1 << endl;

    cout << "the c2 is "<<c2 << endl;

    cout << "the c is "<<c << endl;

}

Type 'abc': asgsgasg

the c1 is a

the c2 is s

the c is sgsgasg          //s被返回到字符流中，被c数组获得

Press any key to continue