整型家族

C 語言基本整型資料類型包括字元、短整型、整型、長整型，皆分為有號與無號兩種版本。

整型值大小規則：長整型至少與整型同長，整型至少與短整型同長。

32/64 位機器上各類型大小參考

long、unsigned long、指標為機器全字長，其大小與 CPU 位數一致。

範圍測試程式碼

#include <stdio.h>
int main() {
    printf("the char range is %-20hhd~%20hhu, size is %u\n", 0x80, 0x7f, sizeof(char));
    printf("the unsigned char range is %-20hhu~%20hhu, size is %u\n", 0x0, 0xff, sizeof(unsigned char));
    printf("the short range is %-20hd~%20hu, size is %u\n", 0x8000, 0x7fff, sizeof(short));
    printf("the unsigned short range is %-20hu~%20hu, size is %u\n", 0x0, 0xffff, sizeof(unsigned short));
    printf("the int range is %-20d~%20u, size is %u\n", 0x80000000, 0x7fffffff, sizeof(int));
    printf("the unsigned int range is %-20u~%20u, size is %u\n", 0x0, 0xffffffff, sizeof(unsigned int));
    printf("the long range is %-20ld~%20lu, size is %u\n", 0x80000000, 0x7fffffff, sizeof(long));
    printf("the unsigned long range is %-20lu~%20lu, size is %u\n", 0x0, 0xffffffff, sizeof(unsigned long));
    printf("the llong range is %-20lld~%20llu, size is %u\n", 0x8000000000000000, 0x7fffffffffffffff, sizeof(long long));
    printf("the unsigned llong range is %-20lld~%20llu, size is %u\n", 0x0ll, 0xffffffffffffffff, sizeof(unsigned long long));
    printf("default constant size is %u %u %u\n", sizeof('b'), sizeof(0x0), sizeof(0x0ll));
}

運行結果

the char range is -128 ~ 127, size is 1
the unsigned char range is 0 ~ 255, size is 1
the short range is -32768 ~ 32767, size is 2
the unsigned short range is 0 ~ 65535, size is 2
the int range is -2147483648 ~ 2147483647, size is 4
the unsigned int range is 0 ~ 4294967295, size is 4
the long range is -2147483648 ~ 2147483647, size is 4
the unsigned long range is 0 ~ 4294967295, size is 4
the llong range is -9223372036854775808 ~ 9223372036854775807, size is 8
the unsigned llong range is 0 ~ 18446744073709551615, size is 8
default constant size is 4 4 8

整型字面值（常數）

• 字面值常數指定自身的值，不允許改變。
• 程式中出現整型常數時，其屬於整型家族中的哪一種類型，取決於書寫方式。可在常數後添加後綴改變預設規則：

• L 或 l：解釋為 long 整型值。
• U 或 u：指定為 unsigned 整型值。
• 同時添加兩者：解釋為 unsigned long 整型值。
• 字元常數類型總是 int，不可添加 unsigned 或 long 後綴。

C 語言一般預設整型常數（字元/整型常數）類型為 int。

printf 輸出格式陷阱

• 若使用 %llu，printf 認為輸出值大小為 8 位元組，若對應參數為 0x0（4 位元組），會讀取 8 位元組導致亂碼。
• printf 輸出整型變數時，打印有號或無號取決於格式字元，與實際傳入參數類型及符號無關。

範例

int i = 0x80001010;
printf("%d\n", i);  // 輸出 -2147479536
printf("%u\n", i);  // 輸出 2147487760
printf("%hu\n", i); // 輸出 4112（高兩位截斷，實際為 0x1010）
printf("%hhu\n", i); // 輸出 16（高三位截斷，實際為 0x10）

結論：使用 printf 打印變數的大小與符號與變數本身無關，即使強制轉型也無效，必須選擇對應正確的格式字元。