Lịch sử các chuẩn C

/* Vi du ve toc do chap nhan trong thuc te:

     C99 ra doi 1999.
     Microsoft Visual C++ ho tro day du C99 vao nam 2019. Hai muoi nam.

     Ly do: MSVC tap trung vao C++, va C++ khong lay het C99.
     Nhieu du an Windows vi vay ket o C89 rat lau.

   Nen "chuan noi gi" va "toi dung duoc gi" la hai cau hoi khac nhau.
   Cau thu hai phu thuoc vao trinh bien dich toi thieu ma du an cua ban
   phai ho tro. */

# Ba muc nghiem ngat, tu long toi chat

gcc -std=c17 prog.c                  # chuan, nhung mo rong GNU van duoc
                                     # chap nhan mot cach im lang

gcc -std=c17 -pedantic prog.c        # CANH BAO khi dung mo rong

gcc -std=c17 -pedantic-errors prog.c # LOI khi dung mo rong  <- nen dung
                                     # neu ban muon ma that su kha chuyen

#include <stdio.h>

int main(void) {
#if !defined(__STDC_VERSION__)
    puts("C89 hoac K&R");
#elif __STDC_VERSION__ == 199409L
    puts("C95");
#elif __STDC_VERSION__ == 199901L
    puts("C99");
#elif __STDC_VERSION__ == 201112L
    puts("C11");
#elif __STDC_VERSION__ == 201710L
    puts("C17");
#elif __STDC_VERSION__ >= 202311L
    puts("C23 hoac moi hon");
#else
    printf("khong ro: %ld\n", __STDC_VERSION__);
#endif
    return 0;
}

# Bon lenh de biet trinh bien dich cua ban lam duoc gi

gcc --version                        # phien ban
gcc -dM -E - < /dev/null | grep STDC # moi macro chuan da dinh nghia
gcc -dM -E - < /dev/null | wc -l     # tong so macro dinh nghia san
echo | gcc -xc -E -v -               # duong dan tim header

# Va mot bai kiem tra cu the:
echo 'int main(void){ return _Generic(1, int:0, default:1); }' \
  | gcc -std=c11 -xc - -o /dev/null && echo "co _Generic"

/* 1. typeof: rat huu ich cho macro */

#if defined(__GNUC__)
  #define DOI_CHO(a, b) do { \
      __typeof__(a) _t = (a); (a) = (b); (b) = _t; } while (0)
#endif

/* C23 chuan hoa thanh "typeof" khong gach duoi.
   Dung "__typeof__" thi chay ca o -std=c17 nghiem ngat, vi ten
   bat dau bang hai gach duoi thuoc ve trinh bien dich. */

/* 2. __attribute__: dung qua mot macro de tat duoc */

#if defined(__GNUC__)
  #define KHONG_TRA_VE  __attribute__((noreturn))
  #define IN_KIEU(a, b) __attribute__((format(printf, a, b)))
#else
  #define KHONG_TRA_VE
  #define IN_KIEU(a, b)
#endif

KHONG_TRA_VE void thoat_voi_loi(const char *tin);
IN_KIEU(1, 2) void ghi_log(const char *dinh_dang, ...);

/* format(printf, 1, 2) rat dang gia: trinh bien dich kiem tra
   dac ta dinh dang cua HAM CUA BAN nhu voi printf. */

/* 3. Mang do dai bien doi o cuoi struct, da chuan hoa o C99 */

struct Goi {
    size_t n;
    char   du_lieu[];      /* C99: dung [] */
    /* char du_lieu[0];       mo rong GNU cu, dung [] thay */
};