char array to double (C++ Learning Community)

Title: char array to double
Description: A little function I made

dr voodoo - August 14, 2003 01:00 PM (GMT)

First of and example prog compile it as console:

CODE

//////////////////
//char to double//
//by Dr Voodoo //
//////////////////
#include <iostream>
using namespace std;

//The first argument is the char array to be converted
//The second is a pointer to a bool. If an error ocures
//this bool will contain true is no error ocures it will
//be false.
double char_to_double(char*str,bool*error)
{
*error=true;
double out=0;
int pos=0;
for(int i=strlen(str)-1;i>=0;i--)
{
switch (str[i])
{
case '0':
case '1':
case '2':
case '3':
case '4':
case '5':
case '6':
case '7':
case '8':
case '9':
{
double val=(double)(str[i]-'0');
for(int i=0;i<pos;i++)
val*=10;
pos++;
out+=val;
}
break;
case ',':
case '.':
{
for(int i=0;i<pos;i++)
out/=10;
pos=0;
}
break;
case '-':
{
if(i!=0)
return 0;
out*=-1;
}
break;
default:
return 0;
}
}
*error=false;
return out;
}

main ()
{
while(1==1)
{
cout<<"Enter a number or enter q to exit:"<<endl;
char char_num[64];
cin>>char_num;
if(char_num[0]=='q')
return 0;
cout<<"Converting char array to double"<<endl;
bool error;
double double_num=char_to_double(char_num,&error);
if(error)
{
cout<<"Error during convertion!"<<endl<<endl;
}
else
{
cout<<"Here is your number this time as double: "<<double_num<<endl<<endl;
}
}
return 0;
}

I have heard many people asking how you could convert a char array containing a number to a numberatic value. I don't know of any function in any header which could do this (although it probably exists) so I wrote my own. It can handel negatif values and fractual values. It doesn't play a roll if you use a "," or a ".". The only downside is that is has problems with large number and I don't know why. Anyway if anyone has use for he is free to use it.

TheHawgMaster - August 14, 2003 03:30 PM (GMT)

atof()
ASCII to floating-point

Look it up in your favorite standard library reference.

KUDOS, though. Nice function.

dr voodoo - August 14, 2003 07:00 PM (GMT)

Oh well, didn't know about it. But it still was interessting to write that function thought. ;)

myork - January 21, 2004 04:50 PM (GMT)

You can use atof().
But my favorate way is to use scanf() as you can check the value had a valid number.

CODE

float value;
if (sscanf(myString,"%f",&value) == 1)
{
// There was a number and 'value' is now valid.
}
else
{
// The string does not contain a number at the start.
}

View Full Version: char array to double