C11 và C23

#include <stdio.h>

#define TEN_KIEU(x) _Generic((x), \
    int: "int", long: "long", double: "double", float: "float", \
    char *: "char *", const char *: "const char *", default: "khac")

int main(void) {
    int i = 1; double d = 2.0; char *s = "a";
    printf("%s %s %s %s\n",
           TEN_KIEU(i), TEN_KIEU(d), TEN_KIEU(s), TEN_KIEU(1L));
    return 0;
}

#include <math.h>
#include <stdlib.h>

#define ABS(x) _Generic((x),          \
    int:         abs,                 \
    long:        labs,                \
    long long:   llabs,               \
    float:       fabsf,               \
    double:      fabs,                \
    long double: fabsl                \
)(x)

/* Bay gio ABS(-3) goi abs, ABS(-3.0f) goi fabsf.
   Do dung la cach tgmath.h duoc cai dat. */

/* Va cho ham cua rieng ban: */

#define IN(x) _Generic((x),                       \
    int:          in_int,                         \
    double:       in_double,                      \
    const char *: in_chuoi,                       \
    char *:       in_chuoi,                       \
    SinhVien *:   in_sinh_vien                    \
)(x)

/* Chu y phai liet ke CA "char *" lan "const char *":
   chung la hai kieu khac nhau, va _Generic khong tu suy dien. */

_Static_assert(sizeof(int) == 4, "ma nay gia dinh int 4 byte");
_Static_assert(CHAR_BIT == 8, "ma nay gia dinh byte 8 bit");
_Static_assert(sizeof(void *) == sizeof(uintptr_t), "uintptr_t phai du");

/* Tu C23 thi ten ngan hon va thong bao la tuy chon: */
static_assert(sizeof(int) == 4, "int 4 byte");
static_assert(sizeof(int) == 4);          /* C23: khong can thong bao */

/* Truoc C23, muon dung ten ngan thi: */
#include <assert.h>       /* dinh nghia static_assert thanh _Static_assert */

#if __STDC_VERSION__ >= 201112L
  #define KIEM_TINH(dk, tin) _Static_assert(dk, tin)
#else
  #define NOI2(a, b) a##b
  #define NOI(a, b)  NOI2(a, b)
  #define KIEM_TINH(dk, tin) \
      typedef char NOI(kiem_tinh_, __LINE__)[(dk) ? 1 : -1]
#endif

KIEM_TINH(sizeof(int) == 4, "can int 4 byte");

/* Ban gia dua vao mot su that: mang co kich thuoc am la loi dich.

   Thong bao xau hon nhieu:
     error: size of array 'kiem_tinh_10' is negative

   Nhung no chay tu C89, va ten mang chua so dong nen ban tim ra cho. */

typedef struct {
    int id;
    struct { int x, y; };     /* nac danh: khong co ten */
} Diem;

int main(void) {
    Diem p;
    p.id = 7;
    p.x = 1;                  /* truy cap THANG, khong phai p.toa_do.x */
    p.y = 2;

    printf("Diem: id=%d x=%d y=%d  sizeof=%d\n",
           p.id, p.x, p.y, (int)sizeof p);
    return 0;
}

/* 1. constexpr: hang so THAT SU, khong phai macro */

constexpr int TOI_DA = 100;
int a[TOI_DA];                    /* dung lam kich thuoc mang: DUOC */
switch (x) { case TOI_DA: ... }   /* dung lam nhan case: DUOC */

/* Truoc C23, "const int TOI_DA = 100" khong lam duoc hai viec do,
   nhu Bai 32.2 da chi ra. Phai dung enum. */

/* 2. typeof: chuan hoa mot mo rong ai cung dung */

#define DOI_CHO(a, b) do { typeof(a) t = (a); (a) = (b); (b) = t; } while (0)
#define TOI_DA(a, b)  ({ typeof(a) _a = (a), _b = (b); _a > _b ? _a : _b; })

/* 3. #embed: nhung tep nhi phan luc DICH */

static const unsigned char bieu_tuong[] = {
    #embed "bieu_tuong.png"
};
static const char giup[] = {
    #embed "giup.txt" suffix(, 0)     /* them ky tu ket thuc chuoi */
};

/* Truoc C23 phai viet mot kich ban sinh ra mang do, va nho chay
   lai moi khi tep goc doi. */

/* 4. Thuoc tinh chuan */

[[nodiscard]] int phai_dung_ket_qua(void);
[[maybe_unused]] int khong_dung;
[[deprecated("dung ham_moi thay the")]] void ham_cu(void);
[[fallthrough]];
[[noreturn]] void thoat(void);