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

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();

2.

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
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

<iomanip>

/*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.

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