{"id":860,"date":"2026-05-08T15:55:57","date_gmt":"2026-05-08T07:55:57","guid":{"rendered":"https:\/\/hsiang.cc\/?p=860"},"modified":"2026-05-05T15:59:21","modified_gmt":"2026-05-05T07:59:21","slug":"c-%e7%9a%84%e9%82%a3%e4%ba%9b%e7%9c%89%e8%a7%92%e5%8f%83%e6%95%b8%e5%82%b3%e9%81%9e%e7%9a%84%e7%9c%89%e8%a7%92-const-%e7%94%a8%e5%b0%8d%e4%ba%86%e5%97%8e%ef%bc%9f","status":"publish","type":"post","link":"https:\/\/hsiang.cc\/?p=860","title":{"rendered":"[C \u7684\u90a3\u4e9b\u7709\u89d2]\u53c3\u6578\u50b3\u905e\u7684\u7709\u89d2 \u2014 `const` \u7528\u5c0d\u4e86\u55ce\uff1f"},"content":{"rendered":"

const<\/code> \u9019\u500b\u95dc\u9375\u5b57\uff0c\u6211\u7528\u4e86\u5f88\u4e45\u90fd\u53ea\u6703\u9019\u6a23\u5beb\uff1a<\/p>\n

const int MAX_SIZE = 256;<\/code><\/pre>\n
\u7136\u5f8c\u5728\u51fd\u5f0f\u53c3\u6578\u4e0a\u5076\u723e\u52a0\u4e00\u4e0b\uff0c
\n\u89ba\u5f97\u300c\u9019\u6a23\u6bd4\u8f03\u5c08\u696d\u300d\uff0c\u4f46\u5176\u5be6\u4e0d\u592a\u78ba\u5b9a\u70ba\u4ec0\u9ebc\u8981\u52a0\u3002<\/p>\n
\u76f4\u5230\u6709\u4e00\u6b21\uff0c\u540c\u4e8b\u5728 code review \u7559\u8a00\uff1a<\/p>\n
\n
\u300c\u9019\u500b\u53c3\u6578\u61c9\u8a72\u52a0 const<\/code>\uff0c\u4f60\u9019\u6a23\u5beb\u547c\u53eb\u7aef\u4e0d\u77e5\u9053\u4f60\u6703\u4e0d\u6703\u6539\u5b83\u3002\u300d<\/p>\n<\/blockquote>\n
\u6211\u624d\u958b\u59cb\u8a8d\u771f\u7814\u7a76 const<\/code> \u5728\u53c3\u6578\u50b3\u905e\u4e0a\u5230\u5e95\u662f\u4ec0\u9ebc\u610f\u601d\u3002<\/p>\n
\u7d50\u679c\u767c\u73fe\uff0cconst<\/code> \u8ddf\u6307\u6a19\u653e\u5728\u4e00\u8d77\uff0c
\n\u5149\u662f\u4f4d\u7f6e\u4e0d\u540c\uff0c\u610f\u601d\u5c31\u5b8c\u5168\u4e0d\u4e00\u6a23\u3002<\/p>\n
<\/p>\n
\n
\u5148\u5f9e\u57fa\u672c\u7684\u8aaa\u8d77<\/h2>\n
\u50b3\u503c\uff08Pass by Value\uff09<\/h3>\n
void foo(int x) {\n    x = 100;  \/\/ \u53ea\u6539\u4e86 local copy\uff0c\u547c\u53eb\u7aef\u7684\u8b8a\u6578\u4e0d\u53d7\u5f71\u97ff\n}\n\nint a = 5;\nfoo(a);\n\/\/ a \u9084\u662f 5<\/code><\/pre>\n
\u50b3\u503c\u7684\u6642\u5019\uff0c\u51fd\u5f0f\u62ff\u5230\u7684\u662f\u4e00\u4efd\u62f7\u8c9d\u3002
\n\u6539\u4e86\u4e0d\u5f71\u97ff\u547c\u53eb\u7aef\uff0c\u6240\u4ee5\u9019\u7a2e\u60c5\u6cc1\u52a0\u4e0d\u52a0 const<\/code> \u5c0d\u547c\u53eb\u7aef\u6c92\u5dee\uff1a<\/p>\n
void foo(const int x) {\n    x = 100;  \/\/ \u7de8\u8b6f\u932f\u8aa4\uff0c\u4f46\u547c\u53eb\u7aef\u672c\u4f86\u5c31\u4e0d\u53d7\u5f71\u97ff\n}<\/code><\/pre>\n
\u50b3\u503c\u52a0 const<\/code>\uff0c\u53ea\u662f\u544a\u8a34\u7de8\u8b6f\u5668\u300c\u9019\u500b local copy \u6211\u4e0d\u6703\u6539\u300d\uff0c
\n\u5c0d\u547c\u53eb\u7aef\u6c92\u6709\u4efb\u4f55\u4fdd\u8b49\u7684\u610f\u7fa9\u3002<\/p>\n
\u5be6\u52d9\u4e0a\uff0c\u50b3\u503c\u7684\u53c3\u6578\u6211\u901a\u5e38\u4e0d\u52a0 const<\/code>\uff0c\u6c92\u4ec0\u9ebc\u5fc5\u8981\u3002<\/p>\n
\n
\u50b3\u6307\u6a19\uff08Pass by Pointer\uff09<\/h3>\n
\u9019\u88e1\u624d\u662f const<\/code> \u771f\u6b63\u6709\u610f\u7fa9\u7684\u5730\u65b9\u3002<\/p>\n
\u50b3\u6307\u6a19\u7684\u6642\u5019\uff0c\u51fd\u5f0f\u53ef\u4ee5\u900f\u904e\u6307\u6a19\u4fee\u6539\u547c\u53eb\u7aef\u7684\u8cc7\u6599\uff0c
\nconst<\/code> \u53ef\u4ee5\u9650\u5236\u9019\u4ef6\u4e8b\u3002<\/p>\n
\u4f46\u554f\u984c\u662f\uff0cconst<\/code> \u8ddf\u6307\u6a19\u653e\u5728\u4e00\u8d77\u6709\u56db\u7a2e\u5beb\u6cd5\uff0c
\n\u6bcf\u7a2e\u610f\u601d\u90fd\u4e0d\u4e00\u6a23\u3002<\/p>\n
\n
const<\/code> \u8207\u6307\u6a19\u7684\u56db\u7a2e\u7d44\u5408<\/h2>\n
\u6211\u7528\u4e00\u500b\u4f8b\u5b50\u4f86\u8aaa\u660e\uff0c\u5047\u8a2d\u6709\u500b uint8_t *p<\/code>\uff1a<\/p>\n
\u7d44\u5408\u4e00\uff1aconst uint8_t *p<\/code>\uff08\u6307\u5411\u5e38\u6578\u7684\u6307\u6a19\uff09<\/h3>\n
void print_data(const uint8_t *p, size_t len) {\n    for (size_t i = 0; i < len; i++) {\n        printf("%02X ", p[i]);  \/\/ \u53ef\u4ee5\u8b80\n    }\n    p[0] = 0xFF;  \/\/ \u274c \u7de8\u8b6f\u932f\u8aa4\uff0c\u4e0d\u80fd\u900f\u904e p \u4fee\u6539\u8cc7\u6599\n}<\/code><\/pre>\n
const<\/code> \u5728 *<\/code> \u5de6\u908a\uff0c\u4ee3\u8868\u6307\u6a19\u6307\u5411\u7684\u5167\u5bb9\u662f\u552f\u8b80\u7684<\/strong>\u3002<\/p>\n
\u51fd\u5f0f\u627f\u8afe\uff1a\u300c\u6211\u53ea\u6703\u8b80\u9019\u584a\u8cc7\u6599\uff0c\u4e0d\u6703\u6539\u5b83\u3002\u300d<\/p>\n
\u9019\u662f\u6700\u5e38\u7528\u7684\u5beb\u6cd5\uff0c\u7528\u5728\u300c\u53ea\u9700\u8981\u8b80\u53d6\u8cc7\u6599\u300d\u7684\u53c3\u6578\u4e0a\u3002<\/p>\n
\n
\u7d44\u5408\u4e8c\uff1auint8_t * const p<\/code>\uff08\u5e38\u6578\u6307\u6a19\uff09<\/h3>\n
void foo(uint8_t * const p, size_t len) {\n    p[0] = 0xFF;   \/\/ \u2705 \u53ef\u4ee5\u4fee\u6539\u6307\u6a19\u6307\u5411\u7684\u5167\u5bb9\n    p = other_buf; \/\/ \u274c \u7de8\u8b6f\u932f\u8aa4\uff0c\u4e0d\u80fd\u6539\u8b8a\u6307\u6a19\u672c\u8eab\n}<\/code><\/pre>\n
const<\/code> \u5728 *<\/code> \u53f3\u908a\uff0c\u4ee3\u8868\u6307\u6a19\u672c\u8eab\u4e0d\u80fd\u6539\u8b8a<\/strong>\uff0c
\n\u4f46\u6307\u5411\u7684\u5167\u5bb9\u53ef\u4ee5\u6539\u3002<\/p>\n
\u9019\u500b\u5728\u51fd\u5f0f\u53c3\u6578\u4e0a\u6bd4\u8f03\u5c11\u7528\uff0c
\n\u56e0\u70ba\u6307\u6a19\u662f\u50b3\u503c\u9032\u4f86\u7684\uff0c\u5c31\u7b97\u6539\u4e86\u4e5f\u4e0d\u5f71\u97ff\u547c\u53eb\u7aef\u3002<\/p>\n
\n
\u7d44\u5408\u4e09\uff1aconst uint8_t * const p<\/code>\uff08\u5e38\u6578\u6307\u6a19\u6307\u5411\u5e38\u6578\uff09<\/h3>\n
void foo(const uint8_t * const p, size_t len) {\n    p[0] = 0xFF;   \/\/ \u274c \u4e0d\u80fd\u6539\u5167\u5bb9\n    p = other_buf; \/\/ \u274c \u4e0d\u80fd\u6539\u6307\u6a19\n}<\/code><\/pre>\n
\u5169\u500b\u90fd\u4e0d\u80fd\u6539\u3002<\/p>\n
\u5be6\u52d9\u4e0a\u6bd4\u8f03\u5c11\u898b\uff0c\u4f46\u5982\u679c\u4f60\u60f3\u8868\u9054\u300c\u9019\u500b\u53c3\u6578\u5b8c\u5168\u552f\u8b80\u300d\uff0c
\n\u9019\u662f\u6700\u56b4\u683c\u7684\u5beb\u6cd5\u3002<\/p>\n
\n
\u7d44\u5408\u56db\uff1auint8_t *p<\/code>\uff08\u4ec0\u9ebc\u90fd\u6c92\u6709\uff09<\/h3>\n
void foo(uint8_t *p, size_t len) {\n    p[0] = 0xFF;   \/\/ \u2705 \u53ef\u4ee5\u6539\u5167\u5bb9\n    p = other_buf; \/\/ \u2705 \u53ef\u4ee5\u6539\u6307\u6a19\uff08\u4f46\u4e0d\u5f71\u97ff\u547c\u53eb\u7aef\uff09\n}<\/code><\/pre>\n
\u6c92\u6709\u4efb\u4f55\u9650\u5236\uff0c\u51fd\u5f0f\u53ef\u4ee5\u4efb\u610f\u4fee\u6539\u6307\u5411\u7684\u5167\u5bb9\u3002<\/p>\n
\n
\u7528\u4e00\u5f35\u8868\u6574\u7406<\/h2>\n\n\n\n\n\n\n\n\n
\u5beb\u6cd5<\/th>\n\u80fd\u6539\u6307\u6a19\u672c\u8eab<\/th>\n\u80fd\u6539\u6307\u5411\u7684\u5167\u5bb9<\/th>\n\u5e38\u7528\u5834\u666f<\/th>\n<\/tr>\n<\/thead>\n
const uint8_t *p<\/code><\/td>\n\u2705<\/td>\n\u274c<\/td>\n\u552f\u8b80\u53c3\u6578\uff08\u6700\u5e38\u7528\uff09<\/td>\n<\/tr>\n
uint8_t * const p<\/code><\/td>\n\u274c<\/td>\n\u2705<\/td>\n\u5c11\u7528<\/td>\n<\/tr>\n
const uint8_t * const p<\/code><\/td>\n\u274c<\/td>\n\u274c<\/td>\n\u5b8c\u5168\u552f\u8b80<\/td>\n<\/tr>\n
uint8_t *p<\/code><\/td>\n\u2705<\/td>\n\u2705<\/td>\n\u9700\u8981\u4fee\u6539\u5167\u5bb9\u7684\u53c3\u6578<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n
\n
\u5be6\u969b\u61c9\u7528\uff1a\u4ec0\u9ebc\u6642\u5019\u8a72\u52a0\uff1f<\/h2>\n
\u53ea\u8b80\u8cc7\u6599\uff0c\u4e00\u5b9a\u8981\u52a0<\/h3>\n
\/\/ \u274c \u6c92\u52a0 const\uff0c\u547c\u53eb\u7aef\u4e0d\u77e5\u9053\u4f60\u6703\u4e0d\u6703\u6539 buf\nint uart_send(uint8_t *buf, size_t len);\n\n\/\/ \u2705 \u52a0\u4e86 const\uff0c\u660e\u78ba\u627f\u8afe\u4e0d\u4fee\u6539 buf\nint uart_send(const uint8_t *buf, size_t len);<\/code><\/pre>\n
\u9019\u500b\u627f\u8afe\u5f88\u91cd\u8981\u3002<\/p>\n
\u547c\u53eb\u7aef\u53ef\u80fd\u50b3\u9032\u4f86\u4e00\u500b const<\/code> \u7684\u8cc7\u6599\uff1a<\/p>\n
const uint8_t greeting[] = "Hello";\nuart_send(greeting, sizeof(greeting));<\/code><\/pre>\n
\u5982\u679c uart_send<\/code> \u7684\u53c3\u6578\u6c92\u6709 const<\/code>\uff0c
\n\u9019\u884c\u6703\u7522\u751f\u7de8\u8b6f\u8b66\u544a\uff08\u751a\u81f3\u932f\u8aa4\uff09\uff0c
\n\u56e0\u70ba\u4f60\u628a const<\/code> \u7684\u6771\u897f\u50b3\u7d66\u4e00\u500b\u300c\u53ef\u80fd\u6703\u6539\u5b83\u300d\u7684\u51fd\u5f0f\u3002<\/p>\n
\n
\u9700\u8981\u4fee\u6539\u5167\u5bb9\uff0c\u4e0d\u8981\u52a0<\/h3>\n
\/\/ \u9019\u500b\u51fd\u5f0f\u8981\u628a\u8cc7\u6599\u5beb\u9032 buf\uff0c\u6240\u4ee5\u4e0d\u80fd\u52a0 const\nint uart_receive(uint8_t *buf, size_t buf_size, uint32_t timeout_ms);<\/code><\/pre>\n
\u9019\u88e1\u4e0d\u52a0 const<\/code> \u662f\u6b63\u78ba\u7684\uff0c
\n\u4ee3\u8868\u300c\u6211\u6703\u628a\u8cc7\u6599\u5beb\u9032\u9019\u500b buffer\u300d\u3002<\/p>\n
\n
\u5b57\u4e32\u53c3\u6578\u5e7e\u4e4e\u90fd\u61c9\u8a72\u52a0<\/h3>\n
\/\/ \u274c\nvoid log_message(char *msg);\n\n\/\/ \u2705\nvoid log_message(const char *msg);<\/code><\/pre>\n
Log \u51fd\u5f0f\u53ea\u9700\u8981\u8b80\u5b57\u4e32\uff0c\u4e0d\u9700\u8981\u6539\u5b83\uff0c
\n\u52a0 const<\/code> \u8b93\u547c\u53eb\u7aef\u53ef\u4ee5\u76f4\u63a5\u50b3\u5b57\u4e32\u5e38\u6578\u9032\u4f86\uff1a<\/p>\n
log_message("System initialized");  \/\/ \u5b57\u4e32\u5e38\u6578\uff0c\u9700\u8981 const \u624d\u4e0d\u6703\u8b66\u544a<\/code><\/pre>\n
\n
\u4e00\u500b\u5e38\u898b\u7684\u8aa4\u89e3<\/h2>\n
\u5f88\u591a\u4eba\u4ee5\u70ba\u52a0\u4e86 const<\/code> \u5c31\u4ee3\u8868\u300c\u9019\u500b\u8b8a\u6578\u4e0d\u6703\u88ab\u6539\u300d\uff0c
\n\u4f46\u5176\u5be6 const<\/code> \u53ef\u4ee5\u88ab cast \u6389\uff1a<\/p>\n
void evil_function(const uint8_t *p) {\n    uint8_t *writable = (uint8_t *)p;  \/\/ cast \u6389 const\n    writable[0] = 0xFF;                \/\/ \u6539\u4e86\uff01\n}<\/code><\/pre>\n
\u9019\u6a23\u505a\u662f undefined behavior\uff0c
\n\u4f46\u7de8\u8b6f\u5668\u4e0d\u4e00\u5b9a\u6703\u5831\u932f\u3002<\/p>\n
\u6240\u4ee5 const<\/code> \u662f\u4e00\u500b\u4ecb\u9762\u4e0a\u7684\u627f\u8afe<\/strong>\uff0c
\n\u4e0d\u662f\u786c\u9ad4\u5c64\u9762\u7684\u4fdd\u8b77\u3002<\/p>\n
\u5b83\u7684\u4e3b\u8981\u4f5c\u7528\u662f\uff1a<\/p>\n