convert char array to double

answerme's Avatar, Join Date: Dec 2007
Ambitious contributor
How can i convert char array to double ,i tried to typecast it but it gave error.
Code:
char tmp[12]=dfdfsdfsd;
double longt;
longt=(double)tmp;
Code:
errorC2440 typecast' : cannot convert from 'char[12]' to 'double'
karthigayan's Avatar, Join Date: Feb 2010
Go4Expert Member
You can not convert the full string to a double .Because when you convert you need just a single value .

Consider the code,

Code:
#include <stdio.h>
main()
{
       
        char c='a';
        double longt;
        longt=(double)c;
        printf("%f\n",longt);
}
Since c is a single character we can convert to a float .
xpi0t0s's Avatar, Join Date: Aug 2004
Mentor
If you want to do a bitwise conversion (which is what you get when you cast) then you need to use either a union or pointers. But don't expect the results to make much sense, because the internal representation of doubles is not ASCII text. If you want the conversion to result in a.x and p containing 3.1415926, then you have to use atof().

Code:
	union {
		char str[12];
		double x;
	} a;

	strcpy(a.str, "3.1415926");
	printf("%e\n",a.x);

	char str1[12];
	strcpy(str1,"3.1415926");
	double *p=(double *)str1; //(1)
	printf("%e\n",*p);

	char str2[12];
	strcpy(str2,"3.1415926");
	printf("%e\n",atof(str2));
(1) Note that what I'm casting here is the pointer to "3.1415926", not the text itself, which is what you tried to do. So I'm creating p as a pointer to a double that is stored at the same location as str1 (which is why the union code does the same thing).