c++ 中double与string之间的转换,char *

运行代码为

 /*
  * main.cpp
  *
  *  Created on: Apr 7, 2016
  *      Author: lizhen
  */

 #include <iostream>
 //#include "MySqrt.h"
 #include <math.h>
 #include <vector>
 #include <typeinfo>
 #include <exception>
 #include <stdexcept>
 #include<string.h>
 #include<sstream>
 #include<stdio.h>

 using namespace std;

 class Base{
 public:
     Base(){
         cout<<"create the base"<<endl;
     }
     virtual ~Base(){
         cout<<"destroy the base"<<endl;
     }
 };
 class Derived: public Base{
 public:
     Derived(){
         cout<<"derived is created"<<endl;
     }
     virtual ~Derived(){
         cout<<"Derived is destroying"<<endl;
     }
 };
 //double -->string
 string doubleConverToString(double d){
     ostringstream os;
     if(os << d) return os.str();
     return "invalid conversion";
 }

 //string-->double
 double stringConverTodouble(string str){
     istringstream iss(str);

     double  x;
     if(iss >> x) return x;
     return 0.0;
 }

 //c-function double-->string
 string cfunctionDtoS(double d){
     char str[];
     sprintf(str,"%.3lf",d);
     return str;
 }
 //c-function string->double
 double cfunctionStoD(string str){
     double dd;
     sscanf(str.c_str(),"%lf",&dd);
     return dd;
 }

 int main() {
     //string-->char*
     string str("string");
     char *p = const_cast<char *>(str.c_str());
     cout<<"string->char*"<<p<<endl;

     //char* -->string
     char *ch = const_cast<char *>("char");//warning: deprecated conversion from string constant to ‘char*’ [-Wwrite-strings]|
     string chstr(ch);
     cout<<"char * -->string"<<chstr<<endl;

     //double&float --->string
     double dd = 3.14;
     string ddstr = doubleConverToString(dd);
     cout<<ddstr<<endl;

     //string--->double&float
     string strp = "3.5555555555";
     double strdd = stringConverTodouble(strp);
     cout<<strdd<<endl;
     cout<<atof(strp.c_str())<<endl;

     //c-function double->string
     string ss = cfunctionDtoS(3.146789);
     cout<<"ss"<<ss<<endl;

     //c-function string->string
     double cdd = cfunctionStoD("3.14259");
     cout<<cdd<<endl;
 }

运行结果

 string->char*string
 char * -->stringchar
 3.14
 3.55556
 3.55556
 ss3.
 3.14259

===========================================================

string-->char*

//string-->char*
    string str("string");
    char *p = const_cast<char *>(str.c_str());
    cout<<"string->char*"<<p<<endl;

char*-->string

//char* -->string
    char *ch = const_cast<char *>("char");//warning: deprecated conversion from string constant to ‘char*’ [-Wwrite-strings]|
    string chstr(ch);
    cout<<"char * -->string"<<chstr<<endl;

===

double/float-->string

string-->double/float

利用c++中 sstream头文件中的方法

==利用 ostringstream 输出流对象,将double输出到string中

方法如下:

//double -->string
string doubleConverToString(double d){
    ostringstream os;
    if(os << d) return os.str();
    return "invalid conversion";
}

==利用istringstream输入流对象,将string中的东西放到double变量中去

方法如下

//string-->double
double stringConverTodouble(string str){
    istringstream iss(str);

    double  x;
    if(iss >> x) return x;
    return 0.0;
}

利用标准c中的stdio.h头文件中的方法

==利用sprintf(str,"%.3lf",dd)方法,将double变量中的字符输出到字符串str中

方法如下:

//c-function double-->string
string cfunctionDtoS(double d){
    char str[];
    sprintf(str,"%.3lf",d);
    return str;
}

==利用sscanf(str,"%d",&dd)方法,将字符串str中的东西,放到double变量dd中

方法如下:

//c-function string->double
double cfunctionStoD(string str){
    double dd;
    sscanf(str.c_str(),"%lf",&dd);
    return dd;
}

 其他方法

char *itoa(int value, char* string, int radix);   int---->string
同样也可以将数字转字符串，不过itoa()这个函数是平台相关的（不是标准里的），故在这里不推荐使用这个函数。

另外也可以使用atoi(),atol(),atof().可以将string--->int/double/float

参考文档:

http://www.cnblogs.com/luxiaoxun/archive/2012/08/03/2621803.html