I have the following source:
int main() { 000J; }
With gcc 4.8.4 it compiles without errors. I know there are suffixes like L or U, but I didn't find anything about J.
So what does it do?
Prefixes − Prefixes denotes the base of the value. For example, 0x10 indicates hexadecimal value with 0x. Suffixes − Suffixes denotes the type of the value. For example, 8465484156155LL denotes a long long integer.
L tells the compiler that the number is of type Long. Long is a signed type greater than or equal to an int in size. On most modern compilers, this means that the number will take 4 bytes of memory.
I get a warning:
Imaginary constants are a GNU extension
The J
suffix is a GNU extension, which causes the literal to be of a _Complex
type.
More info here: https://gcc.gnu.org/onlinedocs/gcc/Complex.html
As zenith mentioned, this is a GNU extension for writing imaginary literals. I really want to comment on the rationale of using j
for this purpose as imallett is wondering but I don't have enough reputation to comment on zenith's answer. I'll leave this as an answer anyway as it might be helpful to others.
As this link explains, both i
and j
can be used to write imaginary literals using this GNU extension. The reason why i
is used for this is obvious, but the reason why j
is used as well is that j
is commonly used to denote the imaginary unit in electrical engineering and control systems engineering to prevent confusion as i
is already used to denote electrical current in those contexts.
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