Re: Does a std::set ever rebalance ?

"Victor Bazarov" <>
Wed, 13 Feb 2008 11:57:02 -0500
mathieu wrote:

 I would like to know if the following piece of code is garantee to
work. I am afraid that the cstring address I am using in the std::map
found from a request in std::set is not garantee to remain the same as
the std::set grows...

Insertions in 'std::set' or 'std::map' do not invalidate iterators
or references. The call to 'find' returns an iterator. You call the
'c_str()' for the object referred to by the iterator. The object is
not going to change unless you remove the entry itself from the set.
So, the pointer returned by 'c_str()' should still be valid up until
the set is destroyed.

At least that's my take on it...


#include <set>
#include <map>
#include <iostream>

struct FileValuePair {
 const char *filename;
 const char *value;

static FileValuePair MAPPINGS[] = {
 { "foo1.dat" , "value1" },
 { "foo2.dat" , "value2" },
 { "foo3.dat" , "value1" },
 { "foo4.dat" , "value3" },
 { "foo5.dat" , "value2" },
 { "foo6.dat" , "value3" },
 { NULL , NULL },

int main()
 FileValuePair *p = MAPPINGS;
 std::set< std::string > values;
 std::map< const char *, const char * > mappings;
   values.insert( p->value );
   // find back the address:
   const char *v = values.find( p->value )->c_str();
    std::map<const char*,const char*>::value_type(p->filename, v));

 std::map<const char*,const char*>::const_iterator it =
 for(; it != mappings.end(); ++it)
   std::cout << it->first << " -> " << it->second << std::endl;

 return 0;

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