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| Redhat8.0/g++ 3.2 hash_map woes! |
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Ziphnor Member since: 11/6/2001 From: Copenhagen |
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 Posted - 10/17/2002 7:13:54 PM |
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| Argghh, i make frequent use of the STL hash_map and curse the fact that it isnt part of the C++ standard... Anyway, in Win32 ive been using STLPort / SGI STL, and hash_maps like for example #include <hash_map> int main() { hash_map } First off, g++ complains about the above, saying it cant find the hash_map include file. So i looked it up, and its in /usr/include/c++/3.2/ext/, so i add that to the include path for g++, and it finds the file just fine. BUT now it complains that 'hash_map' is undeclared.... What am i doing wrong here? Am i using the wrong header? If i use hash_map.h instead(old style) i get a warning about using oldstyle includes, but it compiles.[and i DONT want to change all my hash_map includes to hash_map.h for many reasons  ]Any ideas? |
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Oluseyi Staff Member since: 5/14/2001 From: New York, NY, United States |
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Posted - 10/17/2002 8:33:14 PM |
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| std:: prefix perhaps? Your code example lacks either a using namespace std declaration, a using std::hash_map declaration or explicit qualification of the std::hash_map symbol. |
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Ziphnor Member since: 11/6/2001 From: Copenhagen |
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Posted - 10/18/2002 5:41:03 AM |
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Ooops, but that was a mistake in what i posted here, not in the code i was actually trying to compile(dont know how i managed to screw up a copy-paste? , it was actually
#include <hash_map>
using namespace std;
int main()
{
hash_map<int,int> h;
return 0;
}
Anyway, im still getting the (same) error, any ideas? [edited by - ziphnor on October 18, 2002 5:42:48 AM] |
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Anonymous Poster |
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Posted - 10/18/2002 9:30:57 PM |
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| hash_map is an extension and as such is found in the ext/ directory. Therefore, you'll have to include ext/hash_map. Also, note that the GNU libstdc++ is actually correct: given that hash_map isn't standard, it doesn't belong to the std namespace. You'll find it in the __gnu_cxx namespace (since g++ 3.0 anyway). Finally, the following will fail (at least it does on my systems) :
#include <ext/hash_map>
#include <string>
int main( ) {
__gnu_cxx::hash_map< std::string, std::string > hm;
}
You'll have to specialize the hash for it to work with std::string, like this:
#include <ext/hash_map>
#include <string>
// ideally you'll put this in another namespace as to not
// pollute __gnu_cxx, and provide it as a template
// parameter to hash_map.
namespace __gnu_cxx {
template<>
struct hash< std::string > {
size_t operator( )( std::string const & s ) const {
return __stl_hash_string( s.c_str( ) );
}
};
}
int main( ) {
__gnu_cxx::hash_map< std::string > hm;
}
Of course you could also use your own hashing function/functor. Hope this helps. |
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Ziphnor Member since: 11/6/2001 From: Copenhagen |
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Posted - 10/19/2002 8:08:36 AM |
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| That does indeed explain whats been going on. The old style, worked in Redhat 7.3, but that was gcc 2.95, RH 8 is 3.2. Im not opposed to it being in /ext in any way, seems fair enough, but im not too happy about it, or the namespace, since im trying to write code that compiles on both linux and windows(VS.net)[using SDL+OpenGL]. The hashmap introduces plenty of problems there already as the VS.NET STL library(Dinkum or whatever its called) doesnt use the same syntax as STLPort/SGI. But i thought i had solved this issue by using STLPort with VS.NET. Now i have to include different files depending on the OS, not very neat. Maybe i should just write my own hashmap..... But thanks a lot(!) for clearing this up for me. |
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