sprintf : double precision in C

Question

double a = 0.0000005l;
char aa[50];
sprintf(aa,"%lf",a);
printf("%s",aa);

Output:s0.000000

In the above code snippet, the variable aa can contain only 6 decimal precision. I would like to get an output "s0.0000005". Could you please advice me on how to achieve this? Thanks

Answer 1

You need to write it like sprintf(aa, "%9.7lf", a)

Check out http://en.wikipedia.org/wiki/Printf for some more details on format codes.

Answer 2

The problem is with sprintf

sprintf(aa,"%lf",a);

%lf says to interpet "a" as a "long double" (16 bytes) but it is actually a "double" (8 bytes). Use this instead:

sprintf(aa, "%f", a);

More details here on cplusplus.com

Answer 3

From your question it seems like you are using C99,as you have used %lf for double.

To achieve the desired output replace:

sprintf(aa,"%lf",a);

with

sprintf(aa, "%0.7f", a);

The general syntax "%A.B" means A digits before decimal point & B digits after decimal point :)