C++中数值字符与字符串的相互转换

C++处理字符串和数值时，经常需要相互转换。C++11及以上的<string>就提供了很多类似的函数。

• 字符串转化为数值

Convert from strings

stoi    Convert string to integer (function template )

stol    Convert string to long int (function template )

stoul   Convert string to unsigned integer (function template )

stoll    Convert string to long long (function template )

stoull    Convert string to unsigned long long (function template )

stof       Convert string to float (function template )

stod      Convert string to double (function template )

stold     Convert string to long double (function template )

一般的字符串转化为数值，也有很多是自己写的。核心思想是让字符串的每一位-‘0’。

• 数值转化为字符串std::to_string

string to_string (int val);
string to_string (long val);
string to_string (long long val);
string to_string (unsigned val);
string to_string (unsigned long val);
string to_string (unsigned long long val);
string to_string (float val);
string to_string (double val);
string to_string (long double val);

Convert numerical value to string

Returns a string with the representation of val.

The format used is the same that printf would print for the corresponding type:

type of val	printf equivalent	description
int	"%d"	Decimal-base representation of val. The representations of negative values are preceded with a minus sign (-).
long	"%ld
long long	"%lld
unsigned	"%u"	Decimal-base representation of val.
unsigned long	"%lu
unsigned long long	"%llu
float	"%f"	As many digits are written as needed to represent the integral part, followed by the decimal-point character and six decimal digits. inf (or infinity) is used to represent infinity. nan (followed by an optional sequence of characters) to represent NaNs (Not-a-Number). The representations of negative values are preceded with a minus sign (-).
double	"%f
long double	"%Lf

 

Parameters

val

Numerical value.

Return Value

A string object containing the representation of val as a sequence of characters.