c – 浮动到std :: string转换和本地化

std::string MyClass::doubleToString(double value) const
{
    char fmtbuf[256],buf[256];
    snprintf(fmtbuf,sizeof(fmtbuf)-1,"%s",getDoubleFormat().c_str());
    fmtbuf[sizeof(fmtbuf)-1] = 0;
    snprintf(buf,sizeof(buf)-1,fmtbuf,value);
    buf[sizeof(buf)-1] = 0;

    return std::string(buf);
}

static std::string const& getDoubleFormat() { return "%f"; }

标准C库的 <locale>本地化会影响
格式化输入/输出操作及其字符转换规则和数字格式设置中的小数点字符集.

// On program startup,the locale SELEcted is the "C" standard locale,(equivalent to english). 
printf("Locale is: %s\n",setlocale(LC_ALL,NULL));
cout << doubleToString(3.14)<<endl;
// Switch to system specific locale 
setlocale(LC_ALL,"");  // depends on your environment setTings. 
printf("Locale is: %s\n",NULL));
cout << doubleToString(3.14) << endl;
printf("Locale is: %c\n",localeconv()->thousands_sep);
printf("decimal separator is: %s\n",localeconv()->decimal_point); // get the point

结果是：

Locale is: C
3.140000
Locale is: French_France.1252
3,140000
decimal separator is:,

如果您选择C格式化功能,那么C++ <locale>功能更强大,更灵活.但请注意,C语言环境的设置不会影响C语言环境：

cout << 3.14<<" "<<endl;   // it's still the "C" local 
cout.imbue(locale(""));    // you can set the locale only for one stream if Desired
cout << 3.14 << " "<<1000000<< endl; // localized output

备注：

以下是一个问题：

static std::string const& getDoubleFormat() { return "%f"; }

该函数应返回对字符串的引用.不幸的是,你返回一个字符串文字“％f”,其类型为const char [3].这意味着存在一个隐式转换,它将从const char *构造一个临时字符串并返回其引用.但临时对象在表达式结束时被销毁,因此返回的引用不再有效！

为了测试,我按价值返回.