Terminal L in C

In C, are the follow开发者_开发知识库ing equivalent:

long int x = 3L; (notice the L)

and

long int x = 3

They seem to be the same. In case they are, which one should be used? Should the L be specified explicitly?

If they are different, what is the difference?

3.14L is a long double literal, while 3.14 is a double literal. It won't make much difference in this case, since both are being used to initialize a long int. The result will be 3.

EDIT: Ok, 3L is a long literal, while 3 is an int literal. It still won't make much difference, since the int will be "promoted" to a long. The result will be the same in both cases.

EDIT 2: One place it might make a difference is something like this:

printf("%ld\n", 123);

This is undefined behavior, since the format string specifies a long and only an int is being passed. This would be correct:

printf("%ld\n", 123L);

A decimal integer constant without suffix has - depending on its value - the type int, long, long long, or possibly an implementation-defined extended signed integer type with range greater than long long.

Adding the L suffix means the type will be at least long, the LL suffix means that the type will be at least long long.

If you use the constant to initialize a variable, adding a suffix makes no difference, as the value will be converted to the target-type anyway. However, the type of the constant may well be relevant in more complex expressions as it affects operator semantics, argument promotion and possibly other things I didn't think of right now. For example, assuming a 16-bit int type,

long foo = 42 << 20;

invokes undefined behaviour, whereas

long bar = 42L << 20;

is well-defined.