学习使用点滴-1-字符处理

1.字符转换
1.1 相关类
lexical_cast
bad_lexical_cast
1.2 定义文件：#include <boost/lexical_cast.hpp>
1.3 功能简介：
用来进行类型转换的，字符串与数值之间的转换
1.4 使用举例：
Eclipse 3.0, GUN G++ , Winxp测试通过。
#include <iostream>
#include <boost/lexical_cast.hpp>

using namespace std;

main()
{
int i=100;
char* pstr = "10101";

cout<<"Before convert i is:"<<i<<endl;
i = boost::lexical_cast< int >(pstr);
cout<<"After convert i is:"<<i<<endl;

return 0;
}
//print: Before convert i is:100
// After convert i is:10101

1.5 其他：
转换的异常处理和一般的异常处理相同。
如：try
{
//进行转换
}
catch(bad_lexical_cast &)
{
//处理异常
}

2.格式化字符串
2.1 相关类
format
2.2 定义文件：#include <boost/format.hpp>
2.3 功能简介:
构建一个格式化的字符串，其中的某些字符是待定的，其可以以参数的形式写入。
2.4 使用举例：
Eclipse 3.0, GUN G++ , Winxp测试通过。
#include <iostream>
#include <boost/format.hpp>
#include <string>

using namespace std;

using boost::format;
using boost::io::group;
int main()
{
format fmt("%1% %2% %3% %4% %5% %6%/n");
//使用%1%进行参数替换,1代表第一个参数
string str;
int i=100;
cout<<fmt % 'g' % 'a' % 'l' % 'p' % 'h' % 'y'<<endl;
//%操作符压入参数
string s_tmp =boost::str(fmt);
//str()自由函数,fomat->string
//同样也可使用format.str();

cout << s_tmp;
return 0;
}
2.5 格式说明：
“$“的使用:后面加printf的格式控制符
“|“的使用:简化printf的格式控制符
1.无参数顺序:
format(“%5d %4s %5f“); //%后面直接加printf的格式控制符,参数顺序传入
format(“%|5| %|4| %|5|);//效果同上,自动判断d,s,f等控制符号
2.有参数顺序:
format(“%1% %2% %1%“);
format(“%1$5d %2$5s %1$5d);
format(“%|1$5| %|2$5| %|1$5|);//效果同上,自动判断d,s,f等控制符号
3.具体格式:

[ N$ ] [ flags ] [ 宽度] [ . 精度] type-char

Flag	Meaning	effect on internal stream
'-'	left alignment	N/A (applied later on the string)
'='	centered alignment	N/A (applied later on the string) - note : added feature, not in printf -
'_'	internal alignment	sets internal alignment - note : added feature, not in printf -
'+'	show sign even for positive numbers	sets showpos
'#'	show numerical base, and decimal point	sets showbase and showpoint
'0'	pad with 0's (inserted after sign or base indicator)	if not left-aligned, calls setfill('0') and sets internal Extra actions are taken after stream conversion to handle user-defined output.
' '	if the string does not begin with + or -, insert a space before the converted string	N/A (applied later on the string) Different to printf's behaviour : it is not affected by internal alignment

Type-Char	Meaning	effect on stream
p or x	hexadecimal output	sets hex
o	octal output	sets oct
e	scientific float format	sets floatfield bits to scientific
f	fixed float format	sets floatfield bits to fixed
g	general -default- float format	unset all floatfield bits
X, E or G	same effect as their lowercase counterparts, but using uppercase letters for number outputs. (exponents, hex digits, ..)	same effects as 'x', 'e', or 'g', plus uppercase
d, i or u	decimal type output	sets basefield bits to dec
s or S	string output	precision specification is unset, and its value goes to an internal field for later 'truncation'. (see precision explanation above)
c or C	1-character output	only the first character of the conversion string is used.
%	print the character %	N/A