objective-c - 字段打包字节返回意外结果

Question

根据我的最后一个问题:Field packing to form a single byte，我一直在尝试更改字段打包字节的某些位的值。

但是，根据这些值，我得到了意想不到的结果。顶部代码示例为我提供了 0x91 的预期输出，但是如果我将 colorResolution 和 sizeOfGlobalColorTable 变量更改为:010，我得到了 0x80 的意外输出，这不是它应该是什么的二进制表示:10100010 基于此处:http://www.best-microcontroller-projects.com/hex-code-table.html .我希望底部代码示例的输出为:0xA2。我缺少或不理解什么？

此代码正确记录:0x91

uint8_t screenDescriptorPackedFieldByte = 0;

uint8_t globalColorTableFlag = 1;
uint8_t colorResolution = 001;
uint8_t screenDescriptorSortFlag = 0;
uint8_t sizeOfGlobalColorTable = 001;

screenDescriptorPackedFieldByte |= ((globalColorTableFlag & 0x1) << 7);
screenDescriptorPackedFieldByte |= ((colorResolution & 0x7) << 4);
screenDescriptorPackedFieldByte |= ((screenDescriptorSortFlag & 0x1) << 3);
screenDescriptorPackedFieldByte |= ((sizeOfGlobalColorTable & 0x7) << 0);

NSLog(@"0x%02X",screenDescriptorPackedFieldByte);

此代码错误记录:0x80

uint8_t screenDescriptorPackedFieldByte = 0;

uint8_t globalColorTableFlag = 1;
uint8_t colorResolution = 010;
uint8_t screenDescriptorSortFlag = 0;
uint8_t sizeOfGlobalColorTable = 010;

screenDescriptorPackedFieldByte |= ((globalColorTableFlag & 0x1) << 7);
screenDescriptorPackedFieldByte |= ((colorResolution & 0x7) << 4);
screenDescriptorPackedFieldByte |= ((screenDescriptorSortFlag & 0x1) << 3);
screenDescriptorPackedFieldByte |= ((sizeOfGlobalColorTable & 0x7) << 0);

NSLog(@"0x%02X",screenDescriptorPackedFieldByte);

Answer 1

这个值不是二进制的。是octal .

uint8_t sizeOfGlobalColorTable = 010;

在 (Objective) C 中，从 0 开始的常量被解释为八进制值。你实际写的是b1000 & b0111 = 0。

应该是:

uint8_t sizeOfGlobalColorTable = 0x2;