我试图在逗号是小数分隔符的德国语言环境中一起使用 boost::locale 和 std::stod 。考虑这个代码:

boost::locale::generator gen;

std::locale loc("");  // (1)
//std::locale  loc = gen("");  // (2)

std::locale::global(loc);
std::cout.imbue(loc);

std::string s = "1,1";  //float string in german locale!
double d1 = std::stod(s);
std::cout << "d1: " << d1 << std::endl;

double d2 = 2.2;
std::cout << "d2: " << d2 << std::endl;

d1: 1,1
d2: 2,2

d1: 1
d2: 2.2

std::cout << "d2: " << boost::locale::as::number << d2 << std::endl;

std::locale::global(std::locale(""));
bl::generator gen;
std::locale::global(gen(""));

最佳答案

长话短说: boost::locale仅更改全局 c++-locale 对象，而不更改 C-locale。 stod使用 C-locale 而不是全局 c++-locale 对象。 std::locale两者都改变​​:全局 c++-locale 对象和 C 语言环境。

整个故事: std::locale是一件微妙的事情，负责大量的调试!

让我们从 C++ 类 std::locale 开始:

  std::locale loc("de_DE.utf8");  
  std::cout<<loc.name()<<"\n\n\n";

...
  std::locale loc2;
  std::cout<<loc2.name()<<"\n\n\n";

  std::locale::global(loc);
  std::locale loc3;
  std::cout<<loc3.name()<<"\n\n\n";

  std::locale::global(std::locale::classic());
  std::locale loc4;
  std::cout<<loc4.name()<<"\n\n\n";

 //classical formating
  std::stringstream c_stream;

 //german formating:
  std::locale::global(std::locale("de_DE.utf8"));
  std::stringstream de_stream;

  //same global locale, different results:
  c_stream<<1.1;
  de_stream<<1.1;

  std::cout<<c_stream.str()<<" vs. "<<de_stream.str()<<"\n";

  de_stream.imbue(std::locale::classic());
  de_stream<<" vs. "<<1.1;
  std::cout<<de_stream.str()<<"\n";
  std::cout<<"global c++ state: "<<std::locale().name()<<"\n";

1,1 vs. 1.1
global c++ state: de_DE.utf8

std::cout<<std::stod("1.1")<<" vs. "<<std::stod("1,1")<<"\n";

  std::locale::global(std::locale::classic());
  std::cout<<std::stod("1.1")<<" vs. "<<std::stod("1,1")<<"\n";

std::cout<<"(global) C locale is "<<std::setlocale(LC_ALL,NULL)<<"\n";

  assert(std::setlocale(LC_ALL,"de_DE.utf8")!=NULL);
  std::cout<<"(global) C locale is "<<std::setlocale(LC_ALL,NULL)<<"\n";

std::cout<<"global c++ state: "<<std::locale().name()<<"\n";

std::cout<<"C: "<<std::stod("1.1")<<" vs. DE :"<<std::stod("1,1")<<"\n";

1 vs. 1.1

  std::stringstream stream;//creating with global c++ locale
  stream<<1.1;
  std::cout<<"I'm still in 'C' format: "<<stream.str()<<"\n";

bool s2d(const std::string &str, double  &val, const std::locale &loc=std::locale::classic()){

  std::stringstream ss(str);
  ss.imbue(loc);
  ss>>val;
  return ss.eof() && //all characters interpreted
         !ss.fail(); //nothing went wrong
}

  double d=0;
  std::cout<<"1,1 parsed with German locale successfully :"<<s2d("1,1", d, std::locale("de_DE.utf8"))<<"\n";
  std::cout<<"value retrieved: "<<d<<"\n\n";

  d=0;
  std::cout<<"1,1 parsed with Classical locale successfully :"<<s2d("1,1", d, std::locale::classic())<<"\n";
  std::cout<<"value retrieved: "<<d<<"\n\n";

  d=0;
  std::cout<<"1.1 parsed with German locale successfully :"<<s2d("1.1", d, std::locale("de_DE.utf8"))<<"\n";
  std::cout<<"value retrieved: "<<d<<"\n\n";

  d=0;
  std::cout<<"1.1 parsed with Classical locale successfully :"<<s2d("1.1", d, std::locale::classic())<<"\n";
  std::cout<<"value retrieved: "<<d<<"\n\n";

1,1 parsed with German locale successfully :1
value retrieved: 1.1

1,1 parsed with Classical locale successfully :0
value retrieved: 1

1.1 parsed with German locale successfully :0
value retrieved: 11

1.1 parsed with Classical locale successfully :1
value retrieved: 1.1

关于c++ - stod 不能与 boost::locale 一起正常工作，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/34744911/