C++中int與string的相互轉換

1、int轉string

1.c++11標準增長了全局函數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);
Example:

// to_string example
#include <iostream>   // std::cout
#include <string>     // std::string, std::to_string
 
int main ()
{
  std::string pi = "pi is " + std::to_string(3.1415926);
  std::string perfect = std::to_string(1+2+4+7+14) + " is a perfect number";
  std::cout << pi << '\n';
  std::cout << perfect << '\n';
  return 0;
}
/*
OutPut:
pi is 3.141593
28 is a perfect number
*/

2.採用sstream中定義的字符串流對象來實現

ostringstream os; //構造一個輸出字符串流，流內容爲空 
int i = 12; 
os << i; //向輸出字符串流中輸出int整數i的內容 
cout << os.str() << endl; //利用字符串流的str函數獲取流中的內容

2、string轉int

1.可使用std::stoi/stol/stoll等等函數

Example:

// stoi example
#include <iostream>   // std::cout
#include <string>     // std::string, std::stoi
 
int main ()
{
  std::string str_dec = "2001, A Space Odyssey";
  std::string str_hex = "40c3";
  std::string str_bin = "-10010110001";
  std::string str_auto = "0x7f";
 
  std::string::size_type sz;   // alias of size_t
 
  int i_dec = std::stoi (str_dec,&sz);
  int i_hex = std::stoi (str_hex,nullptr,16);
  int i_bin = std::stoi (str_bin,nullptr,2);
  int i_auto = std::stoi (str_auto,nullptr,0);
 
  std::cout << str_dec << ": " << i_dec << " and [" << str_dec.substr(sz) << "]\n";
  std::cout << str_hex << ": " << i_hex << '\n';
  std::cout << str_bin << ": " << i_bin << '\n';
  std::cout << str_auto << ": " << i_auto << '\n';
 
  return 0;
}
/*
OutPut:
2001, A Space Odyssey: 2001 and [, A Space Odyssey]
40c3:  16579
-10010110001: -1201
0x7f: 127

*/

2.採用標準庫中atoi函數,對於其餘類型也都有相應的標準庫函數，好比浮點型atof(),long型atol()等等

string s = "12"; 
int a = atoi(s.c_str());

3.採用sstream頭文件中定義的字符串流對象來實現轉換

istringstream is("12"); //構造輸入字符串流，流的內容初始化爲「12」的字符串 
int i; 
is >> i; //從is流中讀入一個int整數存入i中