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

Originally Posted by tabstop

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

Yes, it is a shame that this method does not exist in the standard. It is so convenient and so easy for newbies. One for all, and all for one. So to speak.

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