In C++ (and C), a floating point literal without suffix defaults to double
, while the suffix f
implies a float
. But what is the suffix to get a long double
?
Without knowing, I would define, say,
const long double x = 3.14159265358979323846264338328;
But my worry is that the variable x
contains fewer significant bits of 3.14159265358979323846264338328
than 64, because this is a double
literal. Is this worry justified?
In C and related programming languages, long double refers to a floating-point data type that is often more precise than double precision though the language standard only requires it to be at least as precise as double .
The double and long double are two data types used in programming languages such as C++. The main difference between double and long double is that double is used to represent a double precision floating point while long precision is used to represent extended precision floating point value.
Try this instead: cout << "PI = " << setprecision(40) << pi << endl; If you try the above, you would find that the value actually printed will start losing precision after some decimal places(18-25 I guess). The precision of long double in c/c++ is implementation defined.
Rules and Regulations for Using Double in C++ The C++ double should have a floating-point precision of up to 15 digits as it contains a precision that is twice the precision of the float data type. When you declare a variable as double, you should initialize it with a decimal value.
From the C++ Standard
The type of a floating literal is double unless explicitly specified by a suffix. The suffixes f and F specify float, the suffixes l and L specify long double.
It is interesting to compare with corresponding paragraph of the C Standard. In C there is used term floating constant
instead of floating literal
in C++:
4 An unsuffixed floating constant has type double. If suffixed by the letter f or F, it has type float. If suffixed by the letter l or L, it has type long double
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