vswprintf在Mac OS X下某些unicode codepoints失败

Question

我使用GCC和Mac OS X从vswprintf中得到莫名其妙的失败（返回值为-1）（在Mac OS X 10.6和10.8下使用gcc 4.0和4.2.1测试）GCC在Linux下是不是受影响.Visual Studio也是不是受影响）。

为了证明我有最低限度从here适配，使得它打印出vswprintf的返回值的例子问题：

/* vswprintf example */ 
#include <stdio.h> 
#include <stdarg.h> 
#include <wchar.h> 

void PrintWide (const wchar_t * format, ...) 
{ 
    wchar_t buffer[256]; 
    va_list args; 
    va_start (args, format); 
    int res = vswprintf (buffer, 256, format, args); 
    wprintf (L"result=%d\n", res); 
    fputws (buffer, stdout); 
    va_end (args); 
} 

int main() 
{ 
    wchar_t str[] = L"test string has %d wide characters.\n"; 
    PrintWide (str, wcslen(str)); 
    return 0; 
} 

从我的测试看来，取决于str值，vswprintf会有时会失败。例子：

wchar_t str[] = L"test string has %d wide characters.\n"; // works 
wchar_t str[] = L"ßß® test string has %d wide characters.\n"; // works 
wchar_t str[] = L"日本語 test string has %d wide characters.\n"; // FAILS 
wchar_t str[] = L"Π test string has %d wide characters.\n"; // FAILS 
wchar_t str[] = L"\u03A0 test string has %d wide characters.\n"; // FAILS 

看来，包括与Unicode代码点以上0xff字符的任意字符串将触发此问题。任何人都可以阐明为什么会发生这种情况？这似乎是一个太大的问题，以前没有注意到！

Answer 1

如果你设置的语言环境，它应该没问题。要拿起环境变量，你可以这样做：

setlocale(LC_CTYPE, ""); // include <locale.h> 

或者明确设置它。这是因为所有的输出函数都需要知道使用哪种编码。

OS X根本没有执行vswprintf，而Linux运行它（尽管打印时字符会不正确）。

下面是glibc的文档的相关章节：

If the format string contains non-ASCII wide characters, the program 
    will only work correctly if the LC_CTYPE category of the current locale 
    at run time is the same as the LC_CTYPE category of the current locale 
    at compile time. This is because the wchar_t representation is plat‐ 
    form- and locale-dependent. (The glibc represents wide characters 
    using their Unicode (ISO-10646) code point, but other platforms don't 
    do this.