将string转换为double(转)
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![](https://www.cnblogs.com/Images/OutliningIndicators/InBlock.gif)
4
Filename : stringstream_to_double.cpp
5
Compiler : Visual C++ 8.0
6
Description : Demo how to convert string to any type.
7
Release : 11/18/2006
8
*/
9
#include <iostream>
10
#include <sstream>
11
#include <string>
12![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
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template <class T>
14
void convertFromString(T &, const std::string &);
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int main() {
17
std::string s("123");
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// Convert std::string to int
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int i = 0;
21
convertFromString(i,s);
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std::cout << i << std::endl;
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// Convert std::string to double
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double d = 0;
26
convertFromString(d,s);
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std::cout << d << std::endl;
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return 0;
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}
31![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
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template <class T>
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void convertFromString(T &value, const std::string &s) {
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std::stringstream ss(s);
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ss >> value;
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}
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