Re: bizarre backtrace when trying to initialize std::map with std::pair array

[red floyd]

Benjamin Collins wrote:
> I'm trying to initialize a std::map with an array of std::pair, but it
> causes a sigsegv.  I'm using GCC 3.4.6 on RHEL 4.4 x86_64.
>
> My gdb backtrace, a snippet of stl_map.h, and my program are included
> below.  For better formatted display, see http://paste.collinslabs.com/?show=30.
> Notice in particular the values of the parameters to the map
> constructor and the insert_unique() function in frames #3 and #2,
> respectively.  Why is __first in the map constructor one thing, and
> __first in the insert_unique function another?
>
>    1.
>       /* map.cpp */
>    2.
>       #include <iostream>
>    3.
>       #include <map>
>    4.
>       #include <string>
>    5.
>       #include <utility>
>    6.
>       #include <vector>
>    7.
>
>    8.
>       namespace {
>    9.
>         void f() {}
>   10.
>         void g() {}
>   11.
>
>   12.
>         typedef std::pair<std::string, void (*)()> mypair_t;
>   13.
>
>   14.
>         mypair_t pairs[] =
>   15.
>           {
>   16.
>             mypair_t("f", &f),
>   17.
>             mypair_t("g", &g)
>   18.
>           };
>   19.
>       }
>   20.
>
>   21.
>       int main()
>   22.
>       {
>   23.
>         std::map<std::string, void (*)()> mymap(pairs, pairs
> +sizeof(pairs));
>   24.
>       }
>   25.
>
>   26.
You error is on 23.  sizeof(pairs) is much larger than the number of 
entries, so you're running off the end of pairs[].  You either need to 
use sizeof(pairs)/sizeof(mypair_t), or since it's a run-time value:

template<typename T, int N>
inline int array_size(const T(&)[N])
{
    return N;
}

int main()
{
    std::map<std::string, void(*)()> mymap(pairs, array_size(pairs));

}