hash_map中string为key的解决方法
当hash_map中使用string为key时,需用户扩展命名空间,否则报错如下:
/usr/lib/gcc/x86_64-redhat-linux/3.4.5/../../../../include/c++/3.4.5/ext/hashtable.h:518: error: no match for call to `(const __gnu_cxx::hash<std::string>) (const std::basic_string<char, std::char_traits<char>, std::allocator<char> >&)'
表明编译器错误,修改方法有如下几个方案:
方案一:
自己写一个头文件,当使用string为key时,加入该头文件即可。指明了不同编译器下扩展形式。(必杀技)。文件如下:
#ifndef HASH_MAP_HPP
#define HASH_MAP_HPP
#ifdef HAVE_CONFIG_H
#include <config.h>
#endif
#include <string>
#if defined(_STLPORT_VERSION)
#include <hash_map>
#include <hash_set>
using std::hash;
using std::hash_map;
using std::hash_set;
#else // not using STLPORT
#ifdef __GNUC__
#if __GNUC__ >= 3
#include <ext/hash_map>
#include <ext/hash_set>
namespace __gnu_cxx {
template <>
struct hash<std::string> {
size_t operator()(const std::string& s) const {
unsigned long __h = 0;
for (unsigned i = 0;i < s.size();++i)
__h ^= (( __h << 5) + (__h >> 2) + s[i]);
return size_t(__h);
}
};
}
using __gnu_cxx::hash_map;
using __gnu_cxx::hash;
#else // GCC 2.x
#include <hash_map>
#include <hash_set>
namespace std {
struct hash<std::string> {
size_t operator()(const std::string& s) const {
unsigned long __h = 0;
for (unsigned i = 0;i < s.size();++i)
__h ^= (( __h << 5) + (__h >> 2) + s[i]);
return size_t(__h);
}
};
};
using std::hash_map;
using std::hash_set;
using std::hash;
#endif // end GCC >= 3
#elif defined(_MSC_VER) && ((_MSC_VER >= 1300) || defined(__INTEL_COMPILER))
// we only support MSVC7+ and Intel C++ 8.0
#include <hash_map>
#include <hash_set>
namespace stdext {
inline size_t hash_value(const std::string& s) {
unsigned long __h = 0;
for (unsigned i = 0;i < s.size();++i)
__h ^= (( __h << 5) + (__h >> 2) + s[i]);
return size_t(__h);
}
}
using std::hash_map; // _MSC_EXTENSIONS, though DEPRECATED
using std::hash_set;
#else
#error unknown compiler
#endif //GCC or MSVC7+
#endif // end STLPORT
#endif /* ifndef HASH_MAP_HPP */
方案二:
想简单一些,快速使用,可遵照如下写法:
#include <iostream>
#include <string>
#include <ext/hash_map>
using namespace std;
using namespace __gnu_cxx;
namespace __gnu_cxx
{
template<> struct hash<const string>
{
size_t operator()(const string& s) const
{ return hash<const char*>()( s.c_str() ); } //
__stl_hash_string
};
template<> struct hash<string>
{
size_t operator()(const string& s) const
{ return hash<const char*>()( s.c_str() ); }
};
}
int main( void )
{
hash_map<string,int> test;
&n
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