Abstract
std::string为library type，而int、double为built-in type，两者无法利用(int)或(double)的方式互转，本文提出轉換的方式。
Introduction
使用環境：Visual C++ 9.0 / Visual Studio 2008
Method 1：
使用C的atoi()與atof()。
先利用c_str()轉成C string，再用atoi()與atof()。
string_to_double.cpp / C++
1 /*
2 (C) OOMusou 2008 http://oomusou.cnblogs.com
3
4 Filename : string_to_double.cpp
5 Compiler : Visual C++ 9.0 / Visual Studio 2008
6 Description : Demo how to convert string to int (double)
7 Release : 08/01/2008 1.0
8 */
9
10 #include <iostream>
11 #include <string>
12 #include <cstdlib>
13
14 using namespace std;
15
16 int main() {
17 string s = "123";
18 double n = atof(s.c_str());
19 //int n = atoi(s.c_str());
20
21 cout << n << endl;
22 }
2 (C) OOMusou 2008 http://oomusou.cnblogs.com
3
4 Filename : string_to_double.cpp
5 Compiler : Visual C++ 9.0 / Visual Studio 2008
6 Description : Demo how to convert string to int (double)
7 Release : 08/01/2008 1.0
8 */
9
10 #include <iostream>
11 #include <string>
12 #include <cstdlib>
13
14 using namespace std;
15
16 int main() {
17 string s = "123";
18 double n = atof(s.c_str());
19 //int n = atoi(s.c_str());
20
21 cout << n << endl;
22 }
Method 2：
利用stringstream
这里使用functon template的方式将std::string转int、std::string转double。
stringstream_to_double.cpp / C++
1
/*
2
(C) OOMusou 2006 http://oomusou.cnblogs.com
3
4Filename : stringstream_to_double.cpp
5Compiler : Visual C++ 8.0
6Description : Demo how to convert string to any type.
7Release : 11/18/2006
8
*/
9
#include <iostream>
10#include <sstream>
11#include <string>
12
13template <class T>
14void convertFromString(T &, const std::string &);
15
16int main() {
17 std::string s("123");
18
19 // Convert std::string to int
20 int i = 0;
21 convertFromString(i,s);
22 std::cout << i << std::endl;
23
24 // Convert std::string to double
25 double d = 0;
26 convertFromString(d,s);
27 std::cout << d << std::endl;
28
29 return 0;
30}
31
32template <class T>
33void convertFromString(T &value, const std::string &s) {
34 std::stringstream ss(s);
35 ss >> value;
36}
/* 
2
(C) OOMusou 2006 http://oomusou.cnblogs.com3
4
Filename : stringstream_to_double.cpp5
Compiler : Visual C++ 8.06
Description : Demo how to convert string to any type.7
Release : 11/18/20068
*/9
#include <iostream>10
#include <sstream>11
#include <string>12
13
template <class T> 14
void convertFromString(T &, const std::string &);15
16
int main() {
17
std::string s("123");18
19
// Convert std::string to int20
int i = 0;21
convertFromString(i,s);22
std::cout << i << std::endl;23
24
// Convert std::string to double25
double d = 0;26
convertFromString(d,s); 27
std::cout << d << std::endl;28
29
return 0;30
}31
32
template <class T> 33
void convertFromString(T &value, const std::string &s) {34
std::stringstream ss(s);35
ss >> value;36
}