輸入輸出資料流類iostream常用函數解析

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一.成員類型

1. ios::fmtflags：

格式標誌，常用來設定輸出的格式，用於函數flags、setf、unsetf作為其參數或傳回型別。

field	member constant	effect when set
independent flags	boolalpha	read/write bool elements as alphabetic strings (true and false).
	showbase	write integral values preceded by their corresponding numeric base prefix.
	showpoint	write floating-point values including always the decimal point.
	showpos	write non-negative numerical values preceded by a plus sign (+).
	skipws	skip leading whitespaces on certain input operations.
	unitbuf	flush output after each inserting operation.
	uppercase	write uppercase letters replacing lowercase letters in certain insertion operations.
numerical base  (basefield)	dec	read/write integral values using decimal base format.
	hex	read/write integral values using hexadecimal base format.
	oct	read/write integral values using octal base format.
float format  (floatfield)	fixed	write floating point values in fixed-point notation.
	scientific	write floating-point values in scientific notation.
adjustment  (adjustfield)	internal	the output is padded to the field width by inserting fill characters at a specified internal point.
	left	the output is padded to the field width appending fill characters at the end.
	right	the output is padded to the field width by inserting fill characters at the beginning.

 2. ios_base::iostate

flag value	indicates
eofbit	End-Of-File reached while performing an extracting operation on an input stream.
failbit	The last input operation failed because of an error related to the internal logic of the operation itself.
badbit	Error due to the failure of an input/output operation on the stream buffer.
goodbit	No error. Represents the absence of all the above (the value zero).

3. 其他：sentry、event、event_callback、failure、Init、openmode、seekdir

 

二.從輸入資料流類istream繼承的函數

1. gcount：streamsize gcount() const;

返回從最後次非格式化輸入操作中提取的讀取的字元個數

  char str[20];  std::cout << "Please, enter a word: ";  std::cin.getline(str,20);  std::cout << std::cin.gcount() << " characters read: " << str << ‘\n‘;
輸出為：

Please, enter a word: simplify9 characters read: simplify

2. get：int get();讀取一個字元，通常用來排除分行符號的影響

           istream& get (char& c);讀取一個字元到c中

           istream& get (char* s, streamsize n);讀取一個字串，直到遇到分行符號或者讀取了n-1個字元，會自動在末尾添加字元‘\0‘

           istream& get (char* s, streamsize n, char delim);讀取一個字串，直到遇到字元delim或者讀取了n-1個字元，會自動在末尾添加字元‘\0‘

          分行符號會留在輸入隊列中

3. getline：istream& getline (char* s, streamsize n );讀取一個字串，直到遇到分行符號或者讀取了n個字元（分行符號也會讀取），並將分行符號替換為‘\0‘

                istream& getline (char* s, streamsize n, char delim );讀取一個字串，直到遇到字元delim或者讀取了n個字元，並將分行符號替換為‘\0‘

3. ignore：istream& ignore (streamsize n = 1, int delim = EOF);

從輸入隊列中提取字元，並忽略它們，直到提取完前面n個字元或者遇到字元delim為止（delim也提取並忽略）。完成後輸入隊列中的第一個字元為第n+1個字元或者delim後面個字元

  char first, last;  std::cout << "Please, enter your first name followed by your surname: ";  first = std::cin.get();     // get one character  std::cin.ignore(256,‘ ‘);   // ignore until space  last = std::cin.get();      // get one character  std::cout << "Your initials are " << first << last << ‘\n‘;

輸出為：

Please, enter your first name followed by your surname: John SmithYour initials are JS

4. 其他：peek、read、readsome、putback、unget

5. tellg、seekg

6. sync：int sync();

輸入緩衝區同步

 

三、從輸出資料流中繼承的函數

1. put：ostream& put (char c);

輸出字元c

2. 其他：write、tellp、seekp、flush

 

四、保護成員函數（C++11）

=操作、swap

 

五、從ios類繼承來的函數

1. ios::good：bool good() const;

如果錯誤狀態標識（eofbit、failbit、badbit）被設定了返回false，如果沒有返回ture

2. ios::eof：bool eof() const;

如果eofbit被設定了返回ture,說明到達了輸入末尾了

3. fail：bool fail() const;

如果failbit或者badbit被設定了返回true

4. bad：bool bad() const;

如果badbit被設定了返回true

iostate value (member constants)	indicates	functions to check state flags
		good()	eof()	fail()	bad()	rdstate()
goodbit	No errors (zero value iostate)	true	false	false	false	goodbit
eofbit	End-of-File reached on input operation	false	true	false	false	eofbit
failbit	Logical error on i/o operation	false	false	true	false	failbit
badbit	Read/writing error on i/o operation	false	false	true	true	badbit

 5. ios::!操作：

如果failbit或者badbit被設定了返回true

6. ios::clear：void clear (iostate state = goodbit);

為錯誤狀態標識設定新的值

7. ios::fill：char fill() const;返回填充字元

                char fill (char fillch);用字元fillch進行填充，返回填充字元

填充輸出的空閑空間

  char prev;  std::cout.width (10);  std::cout << 40 << ‘\n‘;  prev = std::cout.fill (‘x‘);  std::cout.width (10);  std::cout << 40 << ‘\n‘;  std::cout.fill(prev);

輸出：

40xxxxxxxx40

8. 其他：rdstate、setstate、copyfmt、exceptions、imbue、tie、rdbuf、narrow、widen

 

六、從ios_base類中繼承的函數

1. flags：fmtflags flags() const;返回當前格式

             fmtflags flags (fmtflags fmtfl);設定新的格式，返回之前的格式

  std::cout.flags ( std::ios::right | std::ios::hex | std::ios::showbase );  std::cout.width (10);  std::cout << 100 << ‘\n‘;

輸出：      0x64

2. setf：fmtflags setf (fmtflags fmtfl);

            fmtflags setf (fmtflags fmtfl, fmtflags mask);

設定格式，返回設定之前的格式

  std::cout.setf ( std::ios::hex, std::ios::basefield );  // set hex as the basefield  std::cout.setf ( std::ios::showbase );                  // activate showbase  std::cout << 100 << ‘\n‘;  std::cout.unsetf ( std::ios::showbase );                // deactivate showbase  std::cout << 100 << ‘\n‘;

輸出：

0x6464

3. unset：void unsetf (fmtflags mask);

清空mask選擇的格式

4. precision：streamsize precision() const;返回當前的浮點精度（即小數點位元）

                   streamsize precision (streamsize prec);設定浮點精度，返回之前的浮點精度

5. width：streamsize width() const;返回當前域寬度

              streamsize width (streamsize wide);設定域寬度，返回之前的域寬度

6. 其他：imbue、getloc、xalloc、iword、pword、register_callback、sync_with_stdio

參考：http://www.cplusplus.com/reference/istream/iostream/

 

輸入輸出資料流類iostream常用函數解析