no warning for missing ctor initializer list?-CodePudding

This code is missing a constructor initializer list:

#include <cstdio>

struct s { 
    s() {}  // should be s(): m() {}
    int m;
};

int main() {
    struct s *px = new s();
    if (px->m) {
        printf("true\n");
    } else {
        printf("false\n");
    }
    delete px;
    return 0;
}

gcc compiles cleaning with no warnings:

$ g   -Wall -Wextra -g -O2 test.cpp

However, valgrind knows that the class member m wasn't initialized:

$ valgrind ./a.out
==10953== Conditional jump or move depends on uninitialised value(s)
==10953==    at 0x400512: main (test.cpp:10)
==10953==

Why didn't gcc warn about the missing initialization (-Wmissing-field-initializers or -Wuninitialized or -Wmaybe-uninitialized)?

Is there a flag I can pass that will catch this case?

CodePudding user response：

You could add -Weffc to catch it (inspired by Scott Meyers book "Effective C "). Strangely enough it does not refer to any other -W option (and neither does clang ).

The option is however considered, by some, a bit outdated by now, but in this case, it's finding a real problem.

CodePudding user response：

GCC also has the -fanalyzer flag which does some deeper static analysis than the warning flags do and can catch this specific case on current trunk (but not in GCC 11.2 or earlier):

<source>:10:13: warning: use of uninitialized value '*px.s::m' [CWE-457] [-Wanalyzer-use-of-uninitialized-value]
   10 |     if (px->m) {
      |         ~~~~^
  'int main()': events 1-2
    |
    |    9 |     struct s *px = new s();
    |      |                          ^
    |      |                          |
    |      |                          (1) region created on heap here
    |   10 |     if (px->m) {
    |      |         ~~~~~             
    |      |             |
    |      |             (2) use of uninitialized value '*px.s::m' here
    |

But I often seem to have problems with the flag for generating false positives. For example in this case it complains about operator new potentially returning a null pointer, which cannot ever happen (bug).

See docs for details.