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We are compiling and running user submitted C++ programs in a sandbox environment with the following compile command:

g++ -std=gnu++11 -O2 -o program.exe program.cpp
However, it is possible for users to override compile flags using pragma directives. For example, the optimisation level can be overridden with this code: 
#pragma GCC optimize("Ofast")
We have no control over the source code which is submitted for compilation but we need to prevent compile options from being overridden.

Is there a way to ignore pragma directives with GCC?

puqeko
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From a quick scan of the man page, the answer is "No", gcc has no "disable pragmas" feature.

As a truly ridiculous workaround, you might simple require all entries to omit the string pragma (case-insensitive to block the _Pragma operator as well) entirely, rejecting any that violate that requirement. Anything more complicated that that will essentially entail writing your own C source code parser, and I doubt it's worth the trouble. Not really sure even that will work, given the token concatenation tricks you can play with the preprocessor (I await a comment demonstrating such an exploit).

ShadowRanger
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    Preprosessor tricks should be easy to avoid by first running preprosessor, then filtering/checking the preprosessor output (C code) before compilation. – hyde Jan 08 '19 at 23:47
  • @hyde: True. Depends how flexible their submission system is (it didn't sound very flexible from their question, e.g. they claimed they couldn't control the source code *at all*). – ShadowRanger Jan 09 '19 at 00:29