What is #pragma used for?

Question

Can anyone help me understand #pragma?

ifndef TARGET_OS_LINUX
#pragma once
endif

What,when, where, why, an example?

The above is in

Answer 1

#pragma is just the prefix for a compiler-specific feature.

In this case, #pragma once means that this header file will only ever be included once in a specific destination file. It removes the need for include guards.