C++處理字串和數值時，經常需要相互轉換。C++11及以上的<string>就提供了很多類似的函式。

• 字串轉化為數值

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 )

一般的字串轉化為數值，也有很多是自己寫的。核心思想是讓字串的每一位-‘0’。

• 數值轉化為字串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:

Parameters

val

Numerical value.

Return Value

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