- Breaks the pattern how? We add #pragma once to user-written headers that are meant to be included once and thus also have standard #include guards.
- Whereas include guards would still protect from double definitions, #pragma once may or may not treat them as the same file in a compiler-dependent way.
- The use of #pragma once can reduce build times, as the compiler won’t open and read the file again after the first #include of the file in the translation unit.
- #pragma once is a non-standard pragma that is supported by the vast majority of modern compilers. ... With #pragma once, the same header appears as.
- (opens new window) also support the #pragma once directive which ensures the file is only included once within a single compilation.
- I also found that, at least on GCC, it recognizes the standard #ifndef include guard and optimizes it, so it shouldn’t be much slower than #pragma once .
- Thus, even though #pragma once is demonstrably (slightly) faster, I don’t agree that this in and of itself is a reason to use it over #ifndef guards.
- In C++, #pragma once is a non-standard but widely supported preprocessor directive that serves the same purpose as traditional include guards.
- #pragma once. struct foo { int member ... Wikipedia - #pragma once. Wikipedia - #include guard.
- Instead of having a different macro for every file, that is being included, #pragma once will set the stored include guard macro to __LINE__ during the first pass of the...