cin, cout, ifstream, ofstream, istringstream, ostringstream, <iomanip>

最新推荐文章于 2022-11-11 15:39:42 发布

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本文详细介绍了C++中标准IO流的操作方法，包括输入输出流的使用、错误状态的检查及格式化输出等。同时提供了多种实例演示如何进行字符串、文件的读写以及如何设置输出格式。

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cin

cin >> str;

char c = std::cin.get(); 读入一个字符；

std::istream::get

single character (1)

int get();

istream& get (char& c);

c-string (2)

istream& get (char* s, streamsize n);

istream& get (char* s, streamsize n, char delim);

stream buffer (3)

istream& get (streambuf& sb);

istream& get (streambuf& sb, char delim);

cout

cout << str;

cerr

ifstream

ofstream

fstream不会创建文件，只打开文件并和文件关联起来、关闭文件时和文件解除绑定

fstream

方式1：构造时关联文件；

方式2：构造时为空，open时关联文件；

方式3：构造时为空，读取rdbuf指针，通过此指针open关联文件；（可以看出rdbuf永远不为空，返回filebuf 类型的指针）

常用用法：

1.

std::ostringstream oss;
oss << "One hundred and one: " << 101;
std::string s = oss.str();

用friend <<输出

class Function

{

friend ostream& operator <<(ostream & s_, const Function & desc_);

}

3.
ifstream inputFile("interestingData.txt");
string fileData((istreambuf_iterator<char>(inputFile)),
			istreambuf_iterator<char>());

成员函数判断状态

`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`

/*undefined*/ setw (int n); 设置宽度，用于输入和输出
std::cout << std::setw(10);
/*unspecified*/ setfill (char_type c); 设置填充字符（用于输出ostream）
/*unspecified*/ setprecision (int n); 设置浮点数精度，用于输入和输出
/*unspecified*/ setbase (int base); 设置几进制的数，用于输入和输出
例子：

std::ios_base::setf

fmtflags setf (fmtflags fmtfl);
fmtflags setf (fmtflags fmtfl, fmtflags mask);

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.

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.

`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`