Why is it that scanf()
needs the l
in "%lf
" when reading a double
, when printf()
can use "%f
" regardless of whether its argument is a double
or a float
?
Example code:
double d;
scanf("%lf", &d);
printf("%f", d);
Answer
Because C will promote floats to doubles for functions that take variable arguments. Pointers aren't promoted to anything, so you should be using %lf
, %lg
or %le
(or %la
in C99) to read in doubles.
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