Getting the Narrow Era Names from ICU

ICU-JaEra-NarrowNames.cpp

#include "stdio.h"
#include "icu.h"
#include <string>
#include <sstream>
#include <iostream>
#include <iomanip>
#include <functional>
#include <algorithm>

std::wstring Escape(const std::wstring& s)
{
    std::wostringstream out;
    std::for_each(s.begin(), s.end(),
        [&out](wchar_t ch)
        {
            if (L' ' <= ch && ch <= 0x7f)
            {
                out << ch;
            }
            else
            {
                out << L"\\u" << std::hex << std::setfill(L'0') << std::setw(4) << static_cast<int>(ch);
            }
        });
    return out.str();
}

int main()
{
    UErrorCode status = U_ZERO_ERROR;
    UCalendar* jCal = ucal_open(NULL, 0, "ja_JP@calendar=japanese", UCAL_DEFAULT, &status);
    if (U_FAILURE(status)) {
        printf("FAILED: Line:%d, error: %s\n", __LINE__, u_errorName(status)); return -1;
    }
    ucal_set(jCal, UCAL_EXTENDED_YEAR, 9999);
    int32_t maxEra = ucal_get(jCal, UCAL_ERA, &status);
    if (U_FAILURE(status)) {
        printf("FAILED: Line:%d, error: %s\n", __LINE__, u_errorName(status)); return -1;
    }
    printf("max era number = %d\n", maxEra);

    UChar pattern[] = u"GGGGG"; // This is the pattern for the Era, with narrow width.
    UDateFormat* jUdatFormatter = udat_open(UDAT_PATTERN, UDAT_PATTERN, "ja_JP@calendar=japanese", NULL, 0, pattern, -1, &status);
    if (U_FAILURE(status)) {
        printf("FAILED: Line:%d, error: %s\n", __LINE__, u_errorName(status)); return -1;
    }

    for (int i = maxEra; i >= 0; i--)
    {
        ucal_clear(jCal);
        ucal_set(jCal, UCAL_ERA, i);
        int32_t eYear = ucal_get(jCal, UCAL_EXTENDED_YEAR, &status);
        if (U_FAILURE(status)) {
            printf("FAILED: Line:%d, error: %s\n", __LINE__, u_errorName(status)); return -1;
        }
        printf("era: %d, year: %d\n", i, eYear);

        UDate timestamp = ucal_getMillis(jCal, &status);
        if (U_FAILURE(status)) {
            printf("FAILED: Line:%d, error: %s\n", __LINE__, u_errorName(status)); return -1;
        }
        printf("era: %d, timestamp: %f\n", i, timestamp);

        UChar outputBuffer[256] = {};
        int32_t outputLength = udat_format(jUdatFormatter, timestamp, outputBuffer, 256, nullptr, &status);
        if (U_FAILURE(status)) {
            printf("FAILED: Line:%d, error: %s\n", __LINE__, u_errorName(status)); return -1;
        }

        std::wstring out = Escape(std::wstring((wchar_t*)outputBuffer));
        wprintf(L"Narrow Era Name = '%s'\n", out.c_str());
    }

    std::cout << "Done.\n";
    return 0;
}

/*
The output looks like this:

max era number = 236
era: 236, year: 2019
era: 236, timestamp: 1556694000000.000000
Narrow Era Name = 'R'
era: 235, year: 1989
era: 235, timestamp: 600249600000.000000
Narrow Era Name = 'H'
era: 234, year: 1926
era: 234, timestamp: -1357574400000.000000
Narrow Era Name = 'S'
era: 233, year: 1912
era: 233, timestamp: -1812124800000.000000
Narrow Era Name = 'T'
era: 232, year: 1868
era: 232, timestamp: -3197116052000.000000
Narrow Era Name = 'M'
era: 231, year: 1865
era: 231, timestamp: -3305116052000.000000
Narrow Era Name = '\u6176\u5fdc'
era: 230, year: 1864
era: 230, timestamp: -3340712852000.000000
Narrow Era Name = '\u5143\u6cbb'
era: 229, year: 1861
era: 229, timestamp: -3435407252000.000000
Narrow Era Name = '\u6587\u4e45'
era: 228, year: 1860
era: 228, timestamp: -3464610452000.000000
Narrow Era Name = '\u4e07\u5ef6'
era: 227, year: 1854
...

*/