[cfe-dev] warning for passing NULL as format arg

Matthew Fernandez via cfe-dev cfe-dev at lists.llvm.org
Sat Apr 6 13:57:07 PDT 2019

Hello cfe-dev,

I came across some surprising behavior involving -Wformat. I was generating some C code and an error in the code generator led to it emitting something similar to the following:

    printf(NULL, “foo”);

Using Clang on macOS (version “Apple LLVM version 10.0.0 (clang-1000.11.45.5)”) this compiles warning-free even with -Wformat -Wformat-nonliteral -Wformat-zero-length. Is this to be expected? Obviously it’s quite unlikely a human would write this code, but I was surprised the compiler had nothing to say about this.


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