Thread: changing a string to a 'double' data type

I'm trying to figure out a way to read in two values- one is a char and one is a string. I would like to pull the real number from the string if it is a real number.

basically if the string was a real number it would output as double type.

here's an example of the basic input structure:

Code:

#include <iostream>
#include <string>
using namespace std;

char a;
string b;

cin >> a >> b;

and then somehow would use a function of "strtod" or something similar to extract the real number if there is one.

STRTOD - convert string to double precision number.


here is an example of one that works but w/o the cin value. I have tried using this one below by adding a cin value, but can't get it to work.

Code:

#include <iostream>
#include <stdlib.h>                                                             
#include <stdio.h>  
#include <string>
using namespace std;


/* CELEBS3                                      
   This example converts a string to a double value.                            
   It prints out the converted value and the substring that                     
   stopped the conversion.                                                                                                                                  
 */ 
                                                                                
int main()                                                                  
{                                                                              
	
char *string, *stopstring;                                                   
   double x;                                                                                      

   string = "-5667.45&%$";                                                          
   x = strtod(string, &stopstring);            


   printf("string = \"%s\"\n", string);                                         
   printf("   strtod = %f\n", x);                                               
   printf("   Stopped scan at \"%s\"\n\n", stopstring);            

   cout << x << endl;
   cout << stopstring << endl;

}

and the output is:

string = "-5667.45&%$"
strtod = -5667.450000
Stopped scan at "&%$"

-5667.45
&%$
Press any key to continue . . .


part of that reason is I don't know how to make that strtod function work with a cin command line is I don't know what the asterisks are for on this line: char *string, *stopstring;
I thought if the data type was char, it would be just one letter long. according to the line:
string = "-5667.45&%$";" can have more than one letter...

People always suggest lexical_cast (if you have Boost), so that's one option. The "standard" method is to use a stringstream.

[39] Miscellaneous technical issues, C++ FAQ Lite

thank you, found some good info on stringstreams and does exactly what I needed.