uninitialized var in list

This is a discussion on uninitialized var in list within the C++ Programming forums, part of the General Programming Boards category; Code: #include <list> #include <string> using namespace std; int main () { list<string> mylist; mylist.push_back("test"); } Generates this warning. ..\include\c++.4.5\bits\stl_list.h:435: ...

  1. #1
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    uninitialized var in list

    Code:
    #include <list>
    #include <string>
    using namespace std;
    int main ()
    {
      list<string> mylist;
      mylist.push_back("test");
    }
    Generates this warning.
    ..\include\c++\3.4.5\bits\stl_list.h:435: warning: '__p' might be used uninitialized in this function
    Now I'm not inclined to surf through cryptic library code, but I'm assuming the most basic use of a list should at least compile warning-free.

  2. #2
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    What compiler and what version?

    gcc 4.2.3 on Linux gives me no warning/error even with "-Wall -pedantic -ansi".

  3. #3
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    occurs in both MingW 3.4.4 and 3.4.5 with -w and -pedantic -errors
    I wonder if this is why I get so many retarded warnings with C++....

  4. #4
    C++ Witch laserlight's Avatar
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    Strangely (and yet as expected), I get no warnings when I compile that program with the MinGW port of g++ 3.4.5 on Windows XP SP3.
    Quote Originally Posted by Bjarne Stroustrup (2000-10-14)
    I get maybe two dozen requests for help with some sort of programming or design problem every day. Most have more sense than to send me hundreds of lines of code. If they do, I ask them to find the smallest example that exhibits the problem and send me that. Mostly, they then find the error themselves. "Finding the smallest program that demonstrates the error" is a powerful debugging tool.
    Look up a C++ Reference and learn How To Ask Questions The Smart Way

  5. #5
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    Hmm yeah, I've just tried invoking mingw32-g++ -w -pedantic directly from the command shell and all seems well....

    Well I thought my IDE was purely evil, until I disabled optimizations, and bingo!
    So I tried:
    Code:
    mingw32-g++ test.cpp -Wall -s -Os -O3 -fexpensive-optimizations
    and got it to repro.
    Maybe it's common knowledge, but I was under the impression that compiler optimizations should have no affect on compile-time standards compliance.

  6. #6
    Frequently Quite Prolix dwks's Avatar
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    FWIW: with a few different versions of g++ (4.1, 4.2, and 4.3) under Linux, I get no such warning.
    Code:
    $ cat list.cpp
    #include <list>
    #include <string>
    using namespace std;
    int main ()
    {
      list<string> mylist;
      mylist.push_back("test");
    }
    $ g++
    g++      g++-4.1  g++-4.2  g++-4.3
    $ g++ --version
    g++ (Debian 4.3.1-9) 4.3.1
    Copyright (C) 2008 Free Software Foundation, Inc.
    This is free software; see the source for copying conditions.  There is NO
    warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
    
    $ g++ -Wall -s -Os -O3 -fexpensive-optimizations list.cpp -o list
    $ g++-4.2 -Wall -s -Os -O3 -fexpensive-optimizations list.cpp -o list
    $ g++-4.1 -Wall -s -Os -O3 -fexpensive-optimizations list.cpp -o list
    $
    dwk

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  7. #7
    Cat without Hat CornedBee's Avatar
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    Yeah, GCC only gives such warnings if it computes control and data flow, which it does only when optimizing.

    Possibly 3.4.5's standard library has a bug. The problem of the MinGW project is that they're so far behind in the supported compiler version.
    All the buzzt!
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  8. #8
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    I always use this distribution when I'm on Windows

    http://nuwen.net/mingw.html

    They have gcc 4.2.1 and includes several common libraries (boost, SDL, etc).

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