gcc 未能警告未初始化的变量 [英] gcc failing to warn of uninitialized variable

问题描述

以下代码有一个可能未初始化的变量.似乎 gcc 应该生成警告，但不是:

The following code has a variable that may be uninitialized. It seems that gcc should be generating a warning but isn't:

$ cat a.c
int foo(int b) {
  int a;
  if (b)
    a = 1;
  return a;
}

$ gcc-4.7 -c -Wall -Wmaybe-uninitialized -o a.o ./a.c
$ gcc-4.7 -v
Using built-in specs.
COLLECT_GCC=gcc-4.7
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-linux-gnu/4.7/lto-wrapper
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Ubuntu/Linaro 4.7.3-2ubuntu1~12.04' --with-bugurl=file:///usr/share/doc/gcc-4.7/README.Bugs --enable-languages=c,c++,go,fortran,objc,obj-c++ --prefix=/usr --program-suffix=-4.7 --enable-shared --enable-linker-build-id --libexecdir=/usr/lib --without-included-gettext --enable-threads=posix --with-gxx-include-dir=/usr/include/c++/4.7 --libdir=/usr/lib --enable-nls --with-sysroot=/ --enable-clocale=gnu --enable-libstdcxx-debug --enable-libstdcxx-time=yes --enable-gnu-unique-object --enable-plugin --with-system-zlib --enable-objc-gc --enable-multiarch --disable-werror --with-arch-32=i686 --with-abi=m64 --with-multilib-list=m32,m64 --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 4.7.3 (Ubuntu/Linaro 4.7.3-2ubuntu1~12.04)

有关如何让 gcc 报告未初始化变量的任何线索?

Any clues on how to get gcc to report the uninitialized variable?

推荐答案

看起来你不能 - 见 此错误报告.(还有这个，它被标记为那个人的骗子——它有一个相同的测试你的情况.)因为看起来这个根本原因的错误已经有将近 10 年的历史了，所以这似乎不是一个容易解决的问题.事实上，我链接到的第二个错误在讨论中有永远不会被修复"的短语，所以看起来不太好.

It looks like you can't - see this bug report. (And this one, which is marked as a dupe of that one - it has an identical test case to yours.) Since it looks like the root-cause bug is almost 10 years old, it would seem it's not an easy problem to solve. In fact, the second bug I linked to has the phrase "Never going to be fixed" in the discussion, so that doesn't look good.

如果它对你来说真的很重要，clang 确实用 -Wsometimes-未初始化的，包含在 -Wall 中:

If it's really important to you, clang does catch this one with -Wsometimes-uninitialized, which is included with -Wall:

a.c:3:7: warning: variable 'a' is used uninitialized whenever 'if' condition is
      false [-Wsometimes-uninitialized]
  if (b)
      ^
a.c:5:10: note: uninitialized use occurs here
  return a;
         ^
a.c:3:3: note: remove the 'if' if its condition is always true
  if (b)
  ^~~~~~
a.c:2:8: note: initialize the variable 'a' to silence this warning
  int a;
       ^
        = 0
1 warning generated.

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