C++ FAQ / Section 35 / FAQ 35.17

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Revised Jul 4, 2012

[35.17] How can any human hope to understand these overly verbose template-based error messages?

Here's a free tool that transforms error messages into something more understandable. At the time of this writing, it works with the following compilers: Comeau C++, Intel C++, CodeWarrior C++, gcc, Borland C++, Microsoft Visual C++, and EDG C++.

Here's an example showing some unfiltered gcc error messages:

rtmap.cpp: In function `int main()':
rtmap.cpp:19: invalid conversion from `int' to `
   std::_Rb_tree_node<std::pair<const int, double> >*'
rtmap.cpp:19:   initializing argument 1 of `std::_Rb_tree_iterator<_Val, _Ref,
   _Ptr>::_Rb_tree_iterator(std::_Rb_tree_node<_Val>*) [with _Val =
   std::pair<const int, double>, _Ref = std::pair<const int, double>&, _Ptr =
   std::pair<const int, double>*]'
rtmap.cpp:20: invalid conversion from `int' to `
   std::_Rb_tree_node<std::pair<const int, double> >*'
rtmap.cpp:20:   initializing argument 1 of `std::_Rb_tree_iterator<_Val, _Ref,
   _Ptr>::_Rb_tree_iterator(std::_Rb_tree_node<_Val>*) [with _Val =
   std::pair<const int, double>, _Ref = std::pair<const int, double>&, _Ptr =
   std::pair<const int, double>*]'
E:/GCC3/include/c++/3.2/bits/stl_tree.h: In member function `void
   std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare, _Alloc>::insert_unique(_II,
    _II) [with _InputIterator = int, _Key = int, _Val = std::pair<const int,
   double>, _KeyOfValue = std::_Select1st<std::pair<const int, double> >,
   _Compare = std::less<int>, _Alloc = std::allocator<std::pair<const int,
   double> >]':
E:/GCC3/include/c++/3.2/bits/stl_map.h:272:   instantiated from `void std::map<_
Key, _Tp, _Compare, _Alloc>::insert(_InputIterator, _InputIterator) [with _Input
Iterator = int, _Key = int, _Tp = double, _Compare = std::less<int>, _Alloc = st
d::allocator<std::pair<const int, double> >]'
rtmap.cpp:21:   instantiated from here
E:/GCC3/include/c++/3.2/bits/stl_tree.h:1161: invalid type argument of `unary *
   '

Here's what the filtered error messages look like (note: you can configure the tool so it shows more information; this output was generated with settings to strip things down to a minimum):

rtmap.cpp: In function `int main()':
rtmap.cpp:19: invalid conversion from `int' to `iter'
rtmap.cpp:19:   initializing argument 1 of `iter(iter)'
rtmap.cpp:20: invalid conversion from `int' to `iter'
rtmap.cpp:20:   initializing argument 1 of `iter(iter)'
stl_tree.h: In member function `void map<int,double>::insert_unique(_II, _II)':
    [STL Decryptor: Suppressed 1 more STL standard header message]
rtmap.cpp:21:   instantiated from here
stl_tree.h:1161: invalid type argument of `unary *'

Here is the source code to generate the above example:

#include <map>
#include <algorithm>
#include <cmath>

const int values[] = { 1,2,3,4,5 };
const int NVALS = sizeof values / sizeof (int);

int main()
{
    using namespace std;

    typedef map<int, double> valmap;

    valmap m;

    for (int i = 0; i < NVALS; i++)
        m.insert(make_pair(values[i], pow(values[i], .5)));

    valmap::iterator it = 100;              // error
    valmap::iterator it2(100);              // error
    m.insert(1,2);                          // error

    return 0;
}