Istream函数汇总及输入函数总结

Ø  gcount()

Return values

The extraction count.

 

Remarks

Use basic_istream::get to read unformatted characters.

 

Example

 

#include <iostream> using namespace std; int main( ) { cout << "Type the letter 'a': "; ws( cin ); //Skips white space in the stream. char c[10]; cin.get( &c[0],9 ); cout << c << endl; cout << cin.gcount( ) << endl; }

Ø  get()

int_type get( );

basic_istream& get(

   char_type& _Ch                

);

basic_istream& get(char_type *_Str,  

   streamsize _Count);

basic_istream& get(

   char_type *_Str,                

   streamsize _Count,            

   char_type _Delim

);

Return values

The parameterless form of get returns the element read as an integer or end of file. The remaining forms return the stream (*this).

Remarks

The first of these unformatted input functions extracts an element, if possible, as if by returning rdbuf->sbumpc.   //遍历指针指向的区域

Otherwise, it returns traits_type::eof. If the function extracts no element, it calls setstate(failbit).

 

The second function extracts the int_type element meta the same way. If meta compares equal to traits_type::eof, the function calls setstate(failbit). Otherwise, it stores traits_type::to_char_type(meta) in _Ch. The function returns *this.

 

The third function returns get(_Str, _Count, widen('/n')).

 

The fourth function extracts up to _Count - 1 elements and stores them in the array beginning at _Str. It always stores char_type after any extracted elements it stores.

Example

 

#include <iostream> using namespace std; int main( ) { char c[10]; c[0] = cin.get( ); cin.get( c[1] ); cin.get( &c[2],3 ); cin.get( &c[4], 4, '7' ); cout << c << endl; }

 

Ø  getline()

basic_istream& getline(

   char_type *_Str,

   streamsize _Count

);

basic_istream& getline(

   char_type *_Str,

   streamsize _Count,

   char_type _Delim

);

Return Value

The stream (*this).

Remarks

The first of these unformatted input functions returns getline(_Str, _Count, widen('/n')).

The second function extracts up to _Count - 1 elements and stores them in the array beginning at _Str. It always stores the string termination character after any extracted elements it stores. If the function extracts no elements or _Count - 1 elements, it calls setstate(failbit). In any case, it returns *this

Example

#include <iostream> using namespace std; int main( ) { char c[10]; cin.getline( &c[0], 5, '2' ); cout << c << endl; }

Ø  Read_s()

basic_istream& _Read_s(

    char_type *_Str,

    size_t _Str_size,

    streamsize _Count

);

Return Value

The stream (*this).

Remarks

The unformatted input function extracts up to count elements and stores them in the array beginning at _Str. Extraction stops early on end of file, in which case the function calls setstate(failbit). In any case, it returns *this.

Example

 

 

#include <iostream> using namespace std; int main() { const int c_size = 10; char c[c_size]; int count = 5; cout << "Type 'abcde': "; cin._Read_s(&c[0], c_size, count); c[count] = 0; cout << c << endl; }

Ø  Readsome_s()

streamsize _Readsome_s(

    char_type *_Str,

    size_t _Str_size,

    streamsize _Count

);

Return Value

The count of items in the buffer.

Remarks

The unformatted input function extracts up to count elements and stores them in the array beginning at _Str. If good is false, the function calls setstate(failbit). Otherwise, it assigns the value of rdbuf->in_avail to N. If N < 0, the function calls setstate(eofbit). Otherwise, it replaces the value stored in N with the smaller of _Count and N, and then calls read(_Str, N). In any case, the function returns gcount.

Example

 

 

#include <iostream> using namespace std; int main( ) { const int c_size = 10; char c[c_size]; int count = 5; cout << "Type 'abcdefgh': "; // Can read from buffer or console cin._Read_s(&c[0], c_size, 2); // Can only read from buffer, not from console cin._Readsome_s(&c[0], c_size, count); c[count] = 0; cout << c << endl; }

Ø  ignore()

basic_istream& ignore(

   streamsize _Count = 1,

   int_type _Delim = traits_type::eof( )

);

Return Value

The stream (*this).

Remarks

The unformatted input function extracts up to _Count elements and discards them. If _Count equals numeric_limits<int>::max, however, it is taken as arbitrarily large. Extraction stops early on end of file or on an element _Ch such that traits_type::to_int_type(_Ch) compares equal to _Delim (which is also extracted).

Example

#include <iostream> int main( ) { using namespace std; char chararray[10]; cout << "Type 'abcdef': "; cin.ignore( 5, 'c' ); //’c’is also be ignored cin >> chararray; cout << chararray; }

Ø  gets()

char *gets(

   char* buffer

);

Return Values

Each function returns its argument if successful. A NULL pointer indicates an error or end-of-file condition. Use ferror or feof to determine which one has occurred.

Remarks

The gets function reads a line from the standard input stream stdin and stores it in buffer. The line consists of all characters up to and including the first newline character ('/n').

gets then replaces the newline character with a null character ('/0') before returning the line. In contrast, the fgets function retains the newline character.

Security Remarks

The string to be acquired must not be larger than the maximum number of bytes allowed in buffer; otherwise, a buffer overrun can occur.

This can lead to a denial of service attack against the application if an access violation occurs, or in the worst case, allow an attacker to inject executable code into your process. Consider using an appropriate strsafe function.

Example

 

 

#include <stdio.h> void main( void ) { char line[81]; printf( "Input a string: " ); gets( line ); printf( "The line entered was: %s/n", line ); }

Ø  getchar()

int getchar(

    void

);

Return Values

returns the character read.

To indicate an read error or end-of-file condition, getwchar return WEOF.

Remarks

Each routine reads a single character from a file at the current position and increments the associated file pointer (if defined) to point to the next character.

Example

#include <stdio.h> void main( void ) { char buffer[81]; int i, ch; printf( "Enter a line: " ); /* Read in single line from "stdin": */ for( i = 0; (i < 80) && ((ch = getchar()) != EOF) && (ch != '/n'); i++ ) buffer[i] = (char)ch; /* Terminate string with null character: */ buffer[i] = '/0'; printf( "%s/n", buffer ); }

 

输入函数的总结与对比

语言

函数

获取字符个数

正常返回值

停止输入方式

错误返回值

是否会获取结尾space或'/n'

C++

get

void

1

int

setstate(failbit)

traits_type::eof

NULL

one par

1

the stream (*this)

setstate(failbit)

traits_type::eof

NULL

two par

restricted

the stream (*this)

setstate(failbit)/restricted

traits_type::eof

是

three par

restricted

the stream (*this)

setstate(failbit)/restricted

traits_type::eof

是

getline

two par

restricted

the stream (*this)

setstate(failbit)/restricted

*this

否

three par

restricted

the stream (*this)

setstate(failbit)/restricted

*this

否

Read_s

three par

restricted

the stream (*this)

setstate(failbit)/restricted

*this

是

Readsome_s

three par

restricted

gcount()

setstate(failbit)/restricted

gcount()

否

gets

one par

a line

its argument

error/end-of-file

NULL

否

getchar

void

1

character read

error/end-of-file

WEOF

否

注：Readsome_s()只从输入缓存区读取数据，不再接受cin的输入

 

 

Andy总结于2010年7月10号        22:26:00