Example
If you need to write a file using different locale settings to the default, you can use std::locale and std::basic_ios::imbue() to do that for a specific file stream:
Guidance for use:
- You should always apply a local to a stream before opening the file.
- Once the stream has been imbued you should not change the locale.
Reasons for Restrictions: Imbuing a file stream with a locale has undefined behavior if the current locale is not state independent or not pointing at the beginning of the file.
UTF-8 streams (and others) are not state independent. Also a file stream with a UTF-8 locale may try and read the BOM marker from the file when it is opened; so just opening the file may read characters from the file and it will not be at the beginning.
#include <iostream>
#include <fstream>
#include <locale>
int main()
{
std::cout << "User-preferred locale setting is "
<< std::locale("").name().c_str() << std::endl;
// Write a floating-point value using the user's preferred locale.
std::ofstream ofs1;
ofs1.imbue(std::locale(""));
ofs1.open("file1.txt");
ofs1 << 78123.456 << std::endl;
// Use a specific locale (names are system-dependent)
std::ofstream ofs2;
ofs2.imbue(std::locale("en_US.UTF-8"));
ofs2.open("file2.txt");
ofs2 << 78123.456 << std::endl;
// Switch to the classic "C" locale
std::ofstream ofs3;
ofs3.imbue(std::locale::classic());
ofs3.open("file3.txt");
ofs3 << 78123.456 << std::endl;
}
Explicitly switching to the classic "C" locale is useful if your program uses a different default locale and you want to ensure a fixed standard for reading and writing files. With a "C" preferred locale, the example writes
78,123.456
78,123.456
78123.456
If, for example, the preferred locale is German and hence uses a different number format, the example writes
78 123,456
78,123.456
78123.456
(note the decimal comma in the first line).
