C++：为什么不能编译？

发布于 2024-11-27 03:10:38 字数 1768 浏览 0 评论 0 原文

我有以下从 google 的spareshash 网站获得的 C++ 代码：

#include <iostream>
#include <google/dense_hash_map>
#include <string.h>

using google::dense_hash_map;      // namespace where class lives by default
using std::cout;
using std::endl;
using ext::hash;  // or __gnu_cxx::hash, or maybe tr1::hash, depending on your OS

struct eqstr
{
  bool operator()(const char* s1, const char* s2) const
  {
    return (s1 == s2) || (s1 && s2 && strcmp(s1, s2) == 0);
  }
};

int main(void){
  dense_hash_map<const char*, int, hash<const char*>, eqstr> months;

  months.set_empty_key(NULL);
  months["january"] = 31;
  months["february"] = 28;
  months["march"] = 31;
  months["april"] = 30;
  months["may"] = 31;
  months["june"] = 30;
  months["july"] = 31;
  months["august"] = 31;
  months["september"] = 30;
  months["october"] = 31;
  months["november"] = 30;
  months["december"] = 31;

  cout << "september -> " << months["september"] << endl;
  cout << "april     -> " << months["april"] << endl;
  cout << "june      -> " << months["june"] << endl;
  cout << "november  -> " << months["november"] << endl;
}

我收到以下错误：

using ext::hash

“ext”尚未声明

dense_hash_map, eqstr>月；

“hash”未在此范围内声明

模板参数 3 无效

“,”标记之前应有非限定 ID

预期的初始值设定项位于“>”之前令牌

和months.set_empty_key(NULL);

“months”未在此范围内声明

我是一个 C++ 菜鸟，希望有人能给我指出正确的方向。

预先非常感谢，

原文

I have the following C++ code which I got from google's sparsehash website:

#include <iostream>
#include <google/dense_hash_map>
#include <string.h>

using google::dense_hash_map;      // namespace where class lives by default
using std::cout;
using std::endl;
using ext::hash;  // or __gnu_cxx::hash, or maybe tr1::hash, depending on your OS

struct eqstr
{
  bool operator()(const char* s1, const char* s2) const
  {
    return (s1 == s2) || (s1 && s2 && strcmp(s1, s2) == 0);
  }
};

int main(void){
  dense_hash_map<const char*, int, hash<const char*>, eqstr> months;

  months.set_empty_key(NULL);
  months["january"] = 31;
  months["february"] = 28;
  months["march"] = 31;
  months["april"] = 30;
  months["may"] = 31;
  months["june"] = 30;
  months["july"] = 31;
  months["august"] = 31;
  months["september"] = 30;
  months["october"] = 31;
  months["november"] = 30;
  months["december"] = 31;

  cout << "september -> " << months["september"] << endl;
  cout << "april     -> " << months["april"] << endl;
  cout << "june      -> " << months["june"] << endl;
  cout << "november  -> " << months["november"] << endl;
}

I'm getting the following errors:

using ext::hash

‘ext’ has not been declared

dense_hash_map<const char*, int, hash<const char*>, eqstr> months;

‘hash’ was not declared in this scope

template argument 3 is invalid

expected unqualified-id before ‘,’ token

expected initializer before ‘>’ token

and months.set_empty_key(NULL);