c++ 中double与string之间的转换,char *

运行代码为

  1 /*
  2  * main.cpp
  3  *
  4  *  Created on: Apr 7, 2016
  5  *      Author: lizhen
  6  */
  7 
  8 #include <iostream>
  9 //#include "MySqrt.h"
 10 #include <math.h>
 11 #include <vector>
 12 #include <typeinfo>
 13 #include <exception>
 14 #include <stdexcept>
 15 #include<string.h>
 16 #include<sstream>
 17 #include<stdio.h>
 18 
 19 
 20 using namespace std;
 21 
 22 class Base{
 23 public:
 24     Base(){
 25         cout<<"create the base"<<endl;
 26     }
 27     virtual ~Base(){
 28         cout<<"destroy the base"<<endl;
 29     }
 30 };
 31 class Derived: public Base{
 32 public:
 33     Derived(){
 34         cout<<"derived is created"<<endl;
 35     }
 36     virtual ~Derived(){
 37         cout<<"Derived is destroying"<<endl;
 38     }
 39 };
 40 //double -->string
 41 string doubleConverToString(double d){
 42     ostringstream os;
 43     if(os << d) return os.str();
 44     return "invalid conversion";
 45 }
 46 
 47 //string-->double
 48 double stringConverTodouble(string str){
 49     istringstream iss(str);
 50 
 51     double  x;
 52     if(iss >> x) return x;
 53     return 0.0;
 54 }
 55 
 56 //c-function double-->string
 57 string cfunctionDtoS(double d){
 58     char str[100];
 59     sprintf(str,"%.3lf",d);
 60     return str;
 61 }
 62 //c-function string->double
 63 double cfunctionStoD(string str){
 64     double dd;
 65     sscanf(str.c_str(),"%lf",&dd);
 66     return dd;
 67 }
 68 
 69 int main() {
 70     //string-->char*
 71     string str("string");
 72     char *p = const_cast<char *>(str.c_str());
 73     cout<<"string->char*"<<p<<endl;
 74 
 75     //char* -->string
 76     char *ch = const_cast<char *>("char");//warning: deprecated conversion from string constant to ‘char*’ [-Wwrite-strings]|
 77     string chstr(ch);
 78     cout<<"char * -->string"<<chstr<<endl;
 79 
 80     //double&float --->string
 81     double dd = 3.14;
 82     string ddstr = doubleConverToString(dd);
 83     cout<<ddstr<<endl;
 84 
 85     //string--->double&float
 86     string strp = "3.5555555555";
 87     double strdd = stringConverTodouble(strp);
 88     cout<<strdd<<endl;
 89     cout<<atof(strp.c_str())<<endl;
 90 
 91 
 92 
 93     //c-function double->string
 94     string ss = cfunctionDtoS(3.146789);
 95     cout<<"ss"<<ss<<endl;
 96 
 97     //c-function string->string
 98     double cdd = cfunctionStoD("3.14259");
 99     cout<<cdd<<endl;
100 }

View Code

运行结果

1 string->char*string
2 char * -->stringchar
3 3.14
4 3.55556
5 3.55556
6 ss3.147
7 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