converting a string into a double

Question

I am looking for a way to get floating point input from a user.

My way of going about this is to use a self-made getstrn function and plug that into another function

Answer 1

1. Why are you not using fgets()?
2. You're looking for atof().

(Thanks to R. for fixing my idiotic suggestion in part 1)

Answer 2

Try the strtod function:

char *end;
double num = strtod(arr, &end);

The end will point after the last char that was processed. You can set the second to NULL if you don't care about that. Or you can use atof: atof(str) is equivalent to strtod(str, (char **)NULL).

But you should care, since you can check if the input is malformed:

if (*end != '\0')
  // Handle malformed input

Answer 3

Use strtod, that's what it's for. And fgets can replace your safeGetString function.

Answer 4

Any of:

• strtod()
• atof()
• sscanf()

Of these sscanf offers the strongest validation, since the other two return a valid double value of 0.0 if the input cannot be interpreted as a double, while sscanf() returns the number of format specifiers successfully matched to the input. So:

input_valid = (sscanf( arr, "%lf", value ) != 0 ) ;