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[100];
    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
ss3.147
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[100];
    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