Đọc chuẩn và viết mã khả chuyển

When an expression that has integer type is added to or subtracted
from a pointer, the result has the type of the pointer operand. [...]
if the expression P points to the i-th element of an array object,
the expressions (P)+N (equivalently, N+(P)) and (P)-N (where N has
the value n) point to, respectively, the i+n-th and i-n-th elements
of the array object, provided they exist. Moreover, if the expression
P points to the last element of an array object, the expression (P)+1
points one past the last element of the array object, and if the
expression Q points one past the last element of an array object,
the expression (Q)-1 points to the last element of the array object.
If both the pointer operand and the result point one past the last
element of the array object, the evaluation shall not produce an
overflow; otherwise, the behavior is undefined.

# 1. Chuan nghiem ngat
gcc -std=c17 -pedantic-errors -Wall -Wextra prog.c

# 2. 32 bit, bat gia dinh ve kich thuoc con tro
gcc -m32 -std=c17 prog.c

# 3. Trinh bien dich khac, bat canh bao khac
clang -std=c17 -Wall -Wextra prog.c
clang -Weverything prog.c          # BAT MOI canh bao, rat nhieu bao gia

# 4. Nen tang khac
x86_64-w64-mingw32-gcc prog.c      # Windows tu Linux
arm-none-eabi-gcc prog.c           # ARM, char khong dau

# 5. char khong dau, gia lap ARM tren x86
gcc -funsigned-char prog.c

# 6. Sanitizer, bat gia dinh sai luc chay
gcc -fsanitize=undefined,address prog.c

# .github/workflows/kiem.yml, dai y

chien_luoc:
  ma_tran:
    trinh_bien_dich: [gcc, clang]
    chuan:           [c99, c11, c17]
    do_rong:         [32, 64]
    he:              [ubuntu, macos, windows]

buoc:
  - chay: |
      $CC -std=$CHUAN -m$DO_RONG \
          -pedantic-errors -Wall -Wextra -Werror \
          -fsanitize=undefined,address \
          -o thu *.c
      ./thu

# 2 x 3 x 2 x 3 = 36 to hop. Nhieu, nhung moi to hop chay vai giay
# va chung chay song song.
#
# Trong thuc te, bon to hop dau tien bat gan het van de:
#   gcc  c17 64 ubuntu
#   clang c17 64 macos
#   gcc  c99 32 ubuntu
#   mingw c17 64 windows