在這種情況下，unsigned char和unsigned short之間有什么區別？

Question

我們需要將使用unsigned char作為位掩碼的程序升級到使用unsigned short作為位掩碼的較新版本。 我相信它們之間存在一些差異，因為我們的程序使用相同的邏輯與unsigned char失敗變為unsigned short。 （這是我們購買的外部庫。庫已升級，所以我們也需要更改程序）。

Old version:
typedef struct SomeStruct {
    unsigned char   bit_mask;
#       define      SomeStruct_a_present 0x80
#       define      SomeStruct_b_present 0x40
#       define      SomeStruct_c_present 0x20
    X          x;
    Y          y;
    A          a;  /* optional; set in bit_mask
                                * SomeStruct_a_present if
                                * present */

    B          b;  /* optional; set in bit_mask
                                * SomeStruct_b_present if
                                * present */

    C          c;  /* optional; set in bit_mask
                                * SomeStruct_c_present if
                                * present */
} SomeStruct;



New version:
typedef struct SomeStruct {
    unsigned short   bit_mask;
#       define      SomeStruct_x_present 0x8000
#       define      SomeStruct_y_present 0x4000
#       define      SomeStruct_a_present 0x2000
#       define      SomeStruct_b_present 0x1000
#       define      SomeStruct_c_present 0x0800
    X          x;/* optional; set in bit_mask
                                * SomeStruct_x_present if
                                * present */
    Y          y;/* optional; set in bit_mask
                                * SomeStruct_y_present if
                                * present */
    A          a;  /* optional; set in bit_mask
                                * SomeStruct_a_present if
                                * present */

    B          b;  /* optional; set in bit_mask
                                * SomeStruct_b_present if
                                * present */

    C          c;  /* optional; set in bit_mask
                                * SomeStruct_c_present if
                                * present */
} SomeStruct;

我認為當前行存在一些問題，因為程序崩潰：

我們當前設置bit_mask的方法：

someStruct.bit_mask = SomeStruct_a_present;
someStruct.bit_mask |= SomeStruct_b_present;
someStruct.bit_mask |= SomeStruct_c_present;

Answer 1

用無符號短接這一行

someStruct.bit_mask = SomeStruct_a_present;

將位掩碼的值設置為8192 ，但使用unsigned char時，該值將設置為128 。

原因：

unsigned short是2個字節長，位掩碼是0010000000000000 （ 0x2000 ）但是對於unsigned char，這個值將是10000000 （ 0x80 ）。

Answer 2

 I believe there is some difference between( unsigned short and unsigned char)

sizeof（ unsigned char ）= 1個字節。

sizeof（ unsigned short ）= 2個字節。

Answer 3

“unsigned char”的長度是1 Byte，“unsigned short”的長度是2

Answer 4

從鏈接在這里下的修飾符部分，你可以看到，

sizeof（unsigned char）= 1 Byte and Range = 0 - > +255。

sizeof（unsigned short）= 2 Bytes and Range = 0 - > +65,535。

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