c++ - 在 Mac OS X 上使用 clang llvm3.6 命令行工具的哈希问题

Question

在编译这个由 Bjourne Stroustrup 提供并由我的教授编辑的头文件时遇到问题。我正在使用命令行工具在 OS X 10.10.2 上进行编译。我的编译命令是“gcc -std=C++11 *cpp”，它只是不喜欢这段代码。我在 Linux 和我大学的 Unix 服务器上运行它没有问题。非常感谢任何帮助。

我将包含头文件，然后是错误。

/*std_lib_facilities_4.h
Minimally revised for C++11 features of GCC 4.6.3 or later
Walter C. Daugherity        June 10, 2012 and January 9, 2014
*/

/*
simple "Programming: Principles and Practice using C++" course header to
be used for the first few weeks.
It provides the most common standard headers (in the global namespace)
and minimal exception/error support.

Students: please don't try to understand the details of headers just yet.
All will be explained. This header is primarily used so that you don't have
to understand every concept all at once.

Revised April 25, 2010: simple_error() added
*/

#ifndef H112
#define H112 201401L

#define GCC_VERSION (__GNUC__*10000 + __GNUC_MINOR__*100 + __GNUC_PATCHLEVEL__)

#if GCC_VERSION >= 40603
//New C++11 headers in GCC 4.6.3 or later
#include <array>
#include <regex>
#include <thread>
#include <mutex>
#include <forward_list>
#include <ratio>
#include <tuple>
#include <chrono>
#include <random>
#endif

#include<iostream>
#include<fstream>
#include<sstream>
#include<cmath>
#include<cstdlib>
#include<string>
#include<list>
#include<vector>
#include<algorithm>
#include<stdexcept>

//------------------------------------------------------------------------------

#if GCC_VERSION >= 40603
#include <unordered_map>
#include <unordered_set>
#else
#define unordered_map hash_map
#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());
        }
    };

} // of namespace __gnu_cxx
#endif //_MSC_VER
#endif //GCC_VERSION >= 40603

//------------------------------------------------------------------------------

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, I last) : std::vector<T>(first, last) {}
#if GCC_VERSION >= 40603
    Vector(initializer_list<T> list) : std::vector<T>(list) {}
#endif

    T& operator[](unsigned int i) // rather than return at(i);
    {
        if (this->size() <= i) throw Range_error(i);
        return std::vector<T>::operator[](i);
    }
    const T& operator[](unsigned int i) const
    {
        if (this->size() <= i) throw Range_error(i);
        return std::vector<T>::operator[](i);
    }
};

// disgusting macro hack to get a 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 than return at(i);
    {
        if (size() <= i) throw Range_error(i);
        return std::string::operator[](i);
    }

    const char& operator[](unsigned int i) const
    {
        if (size() <= i) throw Range_error(i);
        return std::string::operator[](i);
    }
};

#ifndef _MSC_VER
#if GCC_VERSION >= 40603
namespace std {

    template<> struct hash<String>
    {
        size_t operator()(const String& s) const
        {
            return hash<std::string>()(s);
        }
    };

} // of namespace std
#else
namespace __gnu_cxx {

    template<> struct hash<String>
    {
        size_t operator()(const String& s) const
        {
            return hash<std::string>()(s);
        }
    };

} // of namespace __gnu_cxx
#endif //GCC_VERSION >= 40603
#endif //_MSC_VER


struct Exit : runtime_error {
    Exit() : runtime_error("Exit") {}
};

// error() simply 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 to get a range checked string:
#define string String
// MS C++ 9.0 have a built-in assert for string range check
// and uses "std::string" in several places so that macro substitution fails
#endif

template<class T> char* as_bytes(T& i)  // needed for binary I/O
{
    void* addr = &i;    // get the address of the first byte
    // of memory used to store the object
    return static_cast<char*>(addr); // treat that memory as bytes
}


inline void keep_window_open()
{
    cin.clear();
    cout << "Please enter a character to exit\n";
    char ch;
    cin >> ch;
    return;
}

inline void keep_window_open(string s)
{
    if (s == "") return;
    cin.clear();
    cin.ignore(120, '\n');
    for (;;) {
        cout << "Please enter " << s << " to exit\n";
        string ss;
        while (cin >> ss && ss != s)
            cout << "Please enter " << s << " to exit\n";
        return;
    }
}



// error function to be used (only) until error() is introduced in Chapter 5:
inline void simple_error(string s)  // write ``error: s and exit program
{
    cerr << "error: " << s << '\n';
    keep_window_open();     // for some Windows environments
    exit(1);
}

// make std::min() and std::max() accessible:
#undef min
#undef max

#include<iomanip>
inline ios_base& general(ios_base& b)   // to augment fixed and 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)); }   // to match C++0x

#endif //H112

下面是错误

./std_lib_facilities.h:43:20: error: no matching function for call to object of
      type 'hash<char *>'
            return hash<char*>()(s.c_str());

Answer 1

为了解释下面奇怪的文件名，我有一个脚本，chkhdr++ ，它检查 C++ 头文件是否可独立编译，以及它是否是幂等的。它创建一个 3 行源文件，例如 /tmp/chkhdr-95127.cpp (数字是进程 ID)包含:

#include HEADER /* Check self-containment */
#include HEADER /* Check idempotency */
int main(void){return 0;}

然后编译它，例如，使用命令行:

 /usr/bin/g++ -std=c++11 -Wall -Wextra -DHEADER=\"stdlibfacilities.h\" -c \
     /tmp/chkhdr-95127.cpp

当我用 stdlibfacilities.h 编译问题的标题(命名为 /usr/bin/g++ )时(这是 XCode 6.3 中的 g++，实际上是 clang++)，我收到错误和警告:

In file included from chkhdr-95127.cpp:1:
In file included from ./stdlibfacilities.h:59:
/Library/Developer/CommandLineTools/usr/bin/../include/c++/v1/ext/hash_map:212:5: warning: Use of
      the header <ext/hash_map> is deprecated. Migrate to <unordered_map> [-W#warnings]
#   warning Use of the header <ext/hash_map> is deprecated.  Migrate to <unordered_map>
    ^
In file included from chkhdr-95127.cpp:1:
./stdlibfacilities.h:68:20: error: no matching function for call to object of type 'hash<char *>'
            return hash<char*>()(s.c_str());
                   ^~~~~~~~~~~~~
/Library/Developer/CommandLineTools/usr/bin/../include/c++/v1/ext/__hash:38:12: note: candidate
      function not viable: 1st argument ('const value_type *' (aka 'const char *')) would lose const
      qualifier
    size_t operator()(char *__c) const _NOEXCEPT
           ^
1 warning and 1 error generated.

关于不可行的候选函数的注释提出了解决该问题的方法——即替换行:

return hash<char*>()(s.c_str());

与:

return hash<const char*>()(s.c_str());

该编译给出:

In file included from chkhdr-95148.cpp:1:
In file included from ./stdlibfacilities.h:59:
/Library/Developer/CommandLineTools/usr/bin/../include/c++/v1/ext/hash_map:212:5: warning: Use of
      the header <ext/hash_map> is deprecated. Migrate to <unordered_map> [-W#warnings]
#   warning Use of the header <ext/hash_map> is deprecated.  Migrate to <unordered_map>
    ^
1 warning generated.

所以，对于大多数问题，有一个简单的解决办法；添加缺失的 const .但是，理想情况下，您应该迁移 header ，以便它使用标准 <unordered_map>而不是 <ext/hash_map> .