[参考]C的scanf 和 C++的fscanf 的用法

说明：本文不适合新手学习，适合用来做参考。本文参考有其他博客的内容，不过年代久远已经忘记了，在此感谢各位博主！

scanf函数

用 法：int scanf(char *format[,argument,...]);          //scanf()函数是通用终端格式化输入函数，它从标准输入设备(键盘) 读取输入的信息。可以读入任何固有类型的数据并自动把数值变换成适当的机内格式。

调用格式： scanf("<格式化字符串>"，<地址表>);    // scanf()函数返回成功赋值的数据项数，出错时则返回EOF。

其控制串由三类字符构成：1、格式化说明符；2、空白符；3、非空白符；

1）格式化说明符

格式字符	说明
%a、%A	读入一个浮点值(仅C99有效)
%f 、 %F、%e、 %E、%g 、%G	读入一个浮点数
%c、%C	读入一个字符
%d	读入十进制整数
%s	读入一个字符串
%p	读入一个指针
%u	读入一个无符号十进制整数
%n	至此已读入值的等价字符数
%[]	扫描字符集合
%%	读%符号
%o	读入八进制整数
%x 、%X	读入十六进制整数
%i	读入十进制，八进制，十六进制整数

2）空白字符

空白字符会使scanf()函数在读操作中略去输入中的一个或多个空白字符，空白符可以是space,tab,newline等等，直到第一个非空白符出现为止。

3）非空白字符

一个非空白字符会使scanf()函数在读入时剔除掉与这个非空白字符相同的字符。

 

fscanf函数

A format specifier for fscanf follows this prototype:     % [*][width][length]specifier 

The format specifier contain sub-specifiers: asterisk (*), width and length (in that order), which are optional and follow these specifications:

sub-specifier	description
*	An optional starting asterisk indicates that the data is to be read from the stream but ignored (i.e. it is not stored in the location pointed by an argument).   注：加上*可将该位置数据忽略
width	Specifies the maximum number of characters to be read in the current reading operation (optional). 注：比如填入7.3,表示整数部分宽度为7，小数部分只读到第3位；也可以不填，不填则将对应数据不带舍入地读入
length	One of hh, h, l, ll, j, z, t, L (optional). This alters the expected type of the storage pointed by the corresponding argument (see the last table).

Where the specifier character at the end is the most significant component, since it defines which characters are extracted, their interpretation and the type of its corresponding argument:

specifier	Description	Characters extracted
i, u	Integer	Any number of digits, optionally preceded by a sign (+ or -). Decimal digits assumed by default (0-9), but a 0 prefix introduces octal digits (0-7), and 0x hexadecimal digits (0-f).
d	Decimal integer （十进制数）	Any number of decimal digits (0-9), optionally preceded by a sign (+ or -).
o	Octal integer	Any number of octal digits (0-7), optionally preceded by a sign (+ or -).
x	Hexadecimal integer (16进制数)	Any number of hexadecimal digits (0-9, a-f, A-F), optionally preceded by 0x or 0X, and all optionally preceded by a sign (+ or -).
f, e, g	Floating point number (浮点数)	A series of decimal digits, optionally containing a decimal point, optionally preceeded by a sign (+ or -) and optionally followed by the e or E character and a decimal integer (or some of the other sequences supported by strtod). Implementations complying with C99 also support hexadecimal floating-point format when preceded by 0x or 0X.
a
c	Character	The next character. If a width other than 1 is specified, the function reads exactlywidth characters and stores them in the successive locations of the array passed as argument. No null character is appended at the end.
s	String of characters	Any number of non-whitespace characters, stopping at the first whitespacecharacter found. A terminating null character is automatically added at the end of the stored sequence.
p	Pointer address	A sequence of characters representing a pointer. The particular format used depends on the system and library implementation, but it is the same as the one used to format %p in fprintf.
[characters]	Scanset	Any number of the characters specified between the brackets. A dash (-) that is not the first character may produce non-portable behavior in some library implementations.
[^characters]	Negated scanset	Any number of characters none of them specified as characters between the brackets.
n	Count	No input is consumed. The number of characters read so far from stream is stored in the pointed location.
%	%	A % followed by another % matches a single %.

Except for n, at least one character shall be consumed by any specifier. Otherwise the match fails, and the scan ends there.

This is a chart showing the types expected for the corresponding arguments where input is stored (both with and without a length sub-specifier):(length放在specifiers前会产生不同的效果，更具体。也可以选择不使用)

	specifiers
length	d i	u o x	f e g a	c s [] [^]	p	n
(none)	int*	unsigned int*	float*	char*	void**	int*
hh	signed char*	unsigned char*				signed char*
h	short int*	unsigned short int*				short int*
l	long int*	unsigned long int*	double*	wchar_t*		long int*
ll	long long int*	unsigned long long int*				long long int*
j	intmax_t*	uintmax_t*				intmax_t*
z	size_t*	size_t*				size_t*
t	ptrdiff_t*	ptrdiff_t*				ptrdiff_t*
L			long double*

Note: Yellow rows indicate specifiers and sub-specifiers introduced by C99.