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Editorial Team
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Asked: 2026-06-06T14:03:44+00:00

I found that my project sets GCC_NO_COMMON_BLOCKS = NO under Apple LLVM Compiler 3.1

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I found that my project sets 

GCC_NO_COMMON_BLOCKS = NO

under Apple LLVM Compiler 3.1 – Code Generation settings, as “No Common Blocks”

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I would like to know: what is that flag used for?

Thanks a lot

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1 Answer

  1. Editorial Team

    From Xcode’s quick help:

    In C, allocate even uninitialized global variables in the data section
    of the object file, rather than generating them as common blocks.
    This has the effect that if the same variable is declared (without
    extern ) in two different compilations, you will get an error when you
    link them. The only reason this might be useful is if you wish to
    verify that the program will work on other systems which always work
    this way.

    You can find the quick help in the right pane, under the “Show Quick Help Inspector” tab:
    Xcode Quick Help Inspector

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