std:: ferror

#include <clocale>
#include <cstdio>
#include <cstdlib>
#include <cwchar>
int main()
{
    const char *fname = std::tmpnam(nullptr);
    std::FILE* f = std::fopen(fname, "wb");
    std::fputs("\xff\xff\n", f); // 非法的UTF-8字符序列
    std::fclose(f);
    std::setlocale(LC_ALL, "en_US.utf8");
    f = std::fopen(fname, "rb");
    std::wint_t ch;
    while ((ch=std::fgetwc(f)) != WEOF) // 尝试以UTF-8格式读取
        std::printf("%#x ", ch);
    if (std::feof(f))
        puts("EOF indicator set");
    if (std::ferror(f))
        puts("Error indicator set");
}