c++ - No matching function for call to object of type 'hash<char">' (Stroustrup Book Drill) -
i starting learning c++ using book, "programming: practice , principles using c++"
in first drill, gave me bit of code run , said should error , should ask else help. that's i'm doing.
the error (as shown in xcode, , within header file):
no matching function call object of type 'hash<char">' this .cpp file
#include "std_lib_facilities.h" int main () { cout << "hello, world!\n"; //output "hello, world!" keep_window_open(); //wait character entered return 0; } the header file: (in xcode, disagreement line return hash<char*>()(s.c_str()); around line 43.
/* simple "programming: principles , practice using c++" course header used first few weeks. provides common standard headers (in global namespace) , minimal exception/error support. students: please don't try understand details of headers yet. explained. header used don't have understand every concept @ once. revised april 25, 2010: simple_error() added */ #ifndef h112 #define h112 201004l #include<iostream> #include<fstream> #include<sstream> #include<cmath> #include<cstdlib> #include<string> #include<list> #include<vector> #include<algorithm> #include<stdexcept> //------------------------------------------------------------------------------ #ifdef _msc_ver #include <hash_map> using stdext::hash_map; #else #include <ext/hash_map> using __gnu_cxx::hash_map; namespace __gnu_cxx { template<> struct hash<std::string> { size_t operator()(const std::string& s) const { return hash<char*>()(s.c_str()); //here is!!!!!!!! } }; } // of namespace __gnu_cxx #endif //------------------------------------------------------------------------------ #define unordered_map hash_map //------------------------------------------------------------------------------ typedef long unicode; //------------------------------------------------------------------------------ using namespace std; template<class t> string to_string(const t& t) { ostringstream os; os << t; return os.str(); } struct range_error : out_of_range { // enhanced vector range error reporting int index; range_error(int i) :out_of_range("range error: "+to_string(i)), index(i) { } }; // trivially range-checked vector (no iterator checking): template< class t> struct vector : public std::vector<t> { typedef typename std::vector<t>::size_type size_type; vector() { } explicit vector(size_type n) :std::vector<t>(n) {} vector(size_type n, const t& v) :std::vector<t>(n,v) {} template <class i> vector(i first, last) :std::vector<t>(first,last) {} t& operator[](unsigned int i) // rather return at(i); { if (i<0||this->size()<=i) throw range_error(i); return std::vector<t>::operator[](i); } const t& operator[](unsigned int i) const { if (i<0||this->size()<=i) throw range_error(i); return std::vector<t>::operator[](i); } }; // disgusting macro hack range checked vector: #define vector vector // trivially range-checked string (no iterator checking): struct string : std::string { string() { } string(const char* p) :std::string(p) {} string(const string& s) :std::string(s) {} template<class s> string(s s) :std::string(s) {} string(int sz, char val) :std::string(sz,val) {} template<class iter> string(iter p1, iter p2) : std::string(p1,p2) { } char& operator[](unsigned int i) // rather return at(i); { if (i<0||size()<=i) throw range_error(i); return std::string::operator[](i); } const char& operator[](unsigned int i) const { if (i<0||size()<=i) throw range_error(i); return std::string::operator[](i); } }; #ifndef _msc_ver namespace __gnu_cxx { template<> struct hash<string> { size_t operator()(const string& s) const { return hash<std::string>()(s); } }; } // of namespace __gnu_cxx #endif struct exit : runtime_error { exit(): runtime_error("exit") {} }; // error() disguises throws: inline void error(const string& s) { throw runtime_error(s); } inline void error(const string& s, const string& s2) { error(s+s2); } inline void error(const string& s, int i) { ostringstream os; os << s <<": " << i; error(os.str()); } #if _msc_ver<1500 // disgusting macro hack range checked string: #define string string // ms c++ 9.0 have built-in assert string range check // , uses "std::string" in several places macro substitution fails #endif template<class t> char* as_bytes(t& i) // needed binary i/o { void* addr = &i; // address of first byte // of memory used store object return static_cast<char*>(addr); // treat memory bytes } inline void keep_window_open() { cin.clear(); cout << "please enter character exit\n"; char ch; cin >> ch; return; } inline void keep_window_open(string s) { if (s=="") return; cin.clear(); cin.ignore(120,'\n'); (;;) { cout << "please enter " << s << " exit\n"; string ss; while (cin >> ss && ss!=s) cout << "please enter " << s << " exit\n"; return; } } // error function used (only) until error() introduced in chapter 5: inline void simple_error(string s) // write ``error: s�� , exit program { cerr << "error: " << s << '\n'; keep_window_open(); // windows environments exit(1); } // make std::min() , std::max() accessible: #undef min #undef max #include<iomanip> inline ios_base& general(ios_base& b) // augment fixed , scientific { b.setf(ios_base::fmtflags(0),ios_base::floatfield); return b; } // run-time checked narrowing cast (type conversion): template<class r, class a> r narrow_cast(const a& a) { r r = r(a); if (a(r)!=a) error(string("info loss")); return r; } inline int randint(int max) { return rand()%max; } inline int randint(int min, int max) { return randint(max-min)+min; } inline double sqrt(int x) { return sqrt(double(x)); } // match c++0x #endif no copyright infringement intended
it's const problem. clang reports: candidate function not viable: 1st argument ('const value_type *' (aka 'const char *')) lose const qualifier.
try:
return hash<const char*>()(s.c_str()); previously had:
return hash<char *>()(s.c_str()); but s.c_str() returns const char * , can't pass const char function that's expecting char *. see c++ const usage explanation of gory detail.
also: top-tip. in xcode when error. press command-4. open little drop down arrow next error see more information, , there's useful, amazing, life-saving, coffee saving additional information :)
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