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POShould gcc warn when an integral enum that evaluates to 0 is used as a pointer?
 

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  1. POShould gcc warn when an integral enum that evaluates to 0 is used as a pointer?
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    <p>The following program compiles with no warnings (which is undesirable, because omitting the array index on lines 19 and 21 effectively destroys the array). If you compile with -D CHECK_NONZERO, you will see that line 23 will not compile without a warning, as the enum BBB evaluates to 1 where AAA and aaa evaluate to 0.</p> <p>It appears that if an enum evaluates to 0, gcc will seamlessly cast it to a NULL pointer.</p> <p>Should this be considered a bug?</p> <p>EDIT: I don't think I was as clear as I could have been about what I perceive to be the issue. It seems to me there would be no harm in type-checking the enum for warning purposes <em>before</em> resolving the enum to its constant value, but this is not how gcc works at the moment. However, I'm not sure if this is worthy of a bug report or feature request to the gcc project.</p> <pre><code>#include &lt;stdio.h&gt; #include &lt;stdlib.h&gt; typedef enum { AAA, BBB, } alpha_e; enum { aaa, bbb, }; int main(void) { alpha_e *alpha_array = malloc(sizeof(*alpha_array) * 2); alpha_array[0] = AAA; alpha_array[1] = BBB; printf("1: alpha_array[0] == %u, alpha_array[1] == %u\n", alpha_array[0], alpha_array[1]); alpha_array = AAA; printf("2: alpha_array[0] == %u, alpha_array[1] == %u\n", alpha_array[0], alpha_array[1]); alpha_array = aaa; #ifdef CHECK_NONZERO alpha_array = BBB; #endif return 1; } </code></pre> <p>gcc -v:</p> <pre><code>Using built-in specs. Target: x86_64-linux-gnu Configured with: ../src/configure -v --with-pkgversion='Ubuntu 4.4.3-4ubuntu5.1' --with-bugurl=file:///usr/share/doc/gcc-4.4/README.Bugs --enable-languages=c,c++,fortran,objc,obj-c++ --prefix=/usr --enable-shared --enable-multiarch --enable-linker-build-id --with-system-zlib --libexecdir=/usr/lib --without-included-gettext --enable-threads=posix --with-gxx-include-dir=/usr/include/c++/4.4 --program-suffix=-4.4 --enable-nls --enable-clocale=gnu --enable-libstdcxx-debug --enable-plugin --enable-objc-gc --disable-werror --with-arch-32=i486 --with-tune=generic --enable-checking=release --build=x86_64-linux-gnu --host=x86_64-linux-gnu --target=x86_64-linux-gnu Thread model: posix gcc version 4.4.3 (Ubuntu 4.4.3-4ubuntu5.1) </code></pre>
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    1. USzsalwasser
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      1. POShould gcc warn when an integral enum that evaluates to 0 is used as a pointer?
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      1. VTUpMod
    1. COI'm trying to think of a context in which setting a pointer to *any* `enum` value would be a good idea and not having a lot of luck. Anyone?
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      1. POShould gcc warn when an integral enum that evaluates to 0 is used as a pointer?
      1. USdmckee
    2. COWhile an enum with value 0 is a valid NULL pointer constant per the standard and gcc doesn't need to produce a diagnostic, it seems that it might be sensible to have a waring that can be enabled/disabled. By default VC++ 2010 produces the following warning: `warning C4047: '=' : 'alpha_e *' differs in levels of indirection from 'int'`
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      1. POShould gcc warn when an integral enum that evaluates to 0 is used as a pointer?
      1. USMichael Burr
 

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