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输入输出流类iostream常用函数解析

news 来源：原创 2024/5/9 3:50:54

原创作品，转载请注明出处：http://www.cnblogs.com/shrimp-can/p/5657192.html

一.成员类型

1. ios::fmtflags：

格式标志，常用来设置输出的格式，用于函数flags、setf、unsetf作为其参数或返回类型。

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.
float format (`floatfield`)	`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.从输入流类istream继承的函数

1. gcount：streamsize gcount() const;

返回从最后次非格式化输入操作中提取的读取的字符个数

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

Please, enter a word: simplify
9 characters read: simplify

2. get：int get();读取一个字符，通常用来排除换行符的影响

istream& get (char& c);读取一个字符到c中

istream& get (char* s, streamsize n);读取一个字符串，直到遇到换行符或者读取了n-1个字符，会自动在末尾添加字符'\0'

istream& get (char* s, streamsize n, char delim);读取一个字符串，直到遇到字符delim或者读取了n-1个字符，会自动在末尾添加字符'\0'

换行符会留在输入队列中

3. getline：istream& getline (char* s, streamsize n );读取一个字符串，直到遇到换行符或者读取了n个字符（换行符也会读取），并将换行符替换为'\0'

istream& getline (char* s, streamsize n, char delim );读取一个字符串，直到遇到字符delim或者读取了n个字符，并将换行符替换为'\0'

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

从输入队列中提取字符，并忽略它们，直到提取完前面n个字符或者遇到字符delim为止（delim也提取并忽略）。完成后输入队列中的第一个字符为第n+1个字符或者delim后面个字符

  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';

输出为：

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

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

5. tellg、seekg

6. sync：int sync();

输入缓冲区同步

三、从输出流中继承的函数

1. put：ostream& put (char c);

输出字符c

2. 其他：write、tellp、seekp、flush

四、保护成员函数（C++11）

=操作、swap

五、从ios类继承来的函数

1. ios::good：bool good() const;

如果错误状态标识（eofbit、failbit、badbit）被设置了返回false，如果没有返回ture

2. ios::eof：bool eof() const;

如果eofbit被设置了返回ture,说明到达了输入末尾了

3. fail：bool fail() const;

如果failbit或者badbit被设置了返回true

4. bad：bool bad() const;

如果badbit被设置了返回true

`iostate` value (member constants)	indicates	functions to check state flags
`iostate` value (member constants)	indicates	`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被设置了返回true

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

为错误状态标识设置新的值

7. ios::fill：char fill() const;返回填充字符

char fill (char fillch);用字符fillch进行填充，返回填充字符

填充输出的空闲空间

  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);

输出：

40
xxxxxxxx40

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

六、从ios_base类中继承的函数

1. flags：fmtflags flags() const;返回当前格式

fmtflags flags (fmtflags fmtfl);设置新的格式，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';

输出： 0x64

2. setf：fmtflags setf (fmtflags fmtfl);

fmtflags setf (fmtflags fmtfl, fmtflags mask);

设置格式，返回设置之前的格式

  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';

输出：