{"id":84841,"date":"2020-05-13T10:19:44","date_gmt":"2020-05-13T02:19:44","guid":{"rendered":"http:\/\/4563.org\/?p=84841"},"modified":"2020-05-13T10:19:44","modified_gmt":"2020-05-13T02:19:44","slug":"read-%e5%87%bd%e6%95%b0%e7%ac%ac%e4%b8%89%e4%b8%aa%e5%8f%82%e6%95%b0%e6%98%af%e4%b8%8d%e5%b8%a6%e7%ac%a6%e5%8f%b7%e7%9a%84%e6%95%b4%e5%9e%8b%ef%bc%8c%e8%bf%94%e5%9b%9e%e5%80%bc%e6%98%af%e5%b8%a6","status":"publish","type":"post","link":"http:\/\/4563.org\/?p=84841","title":{"rendered":"read \u51fd\u6570\u7b2c\u4e09\u4e2a\u53c2\u6570\u662f\u4e0d\u5e26\u7b26\u53f7\u7684\u6574\u578b\uff0c\u8fd4\u56de\u503c\u662f\u5e26\u7b26\u53f7\u7684\u6574\u578b\uff0c\u8fd9\u4e48\u8bbe\u8ba1\u611f\u89c9\u4e0d\u5408\u7406\u554a"},"content":{"rendered":"
\n
\n
\n

read \u51fd\u6570\u7b2c\u4e09\u4e2a\u53c2\u6570\u662f\u4e0d\u5e26\u7b26\u53f7\u7684\u6574\u578b\uff0c\u8fd4\u56de\u503c\u662f\u5e26\u7b26\u53f7\u7684\u6574\u578b\uff0c\u8fd9\u4e48\u8bbe\u8ba1\u611f\u89c9\u4e0d\u5408\u7406\u554a <\/h1>\n

<\/p>\n

\n
\u8cc7\u6df1\u5927\u4f6c : lolcat <\/span> <\/i> 3<\/span> <\/div>\n
<\/div>\n<\/p><\/div>\n<\/p><\/div>\n<\/p><\/div>\n
<\/p>\n

ssize_t read(int fd, void *buf, size_t count);<\/code><\/p>\n

\u8fd4\u56de\u503c\u662f\u5e26\u7b26\u53f7\u7684 ssize_t\uff0c\u4ee3\u8868\u6b64\u6b21 read \u5b9e\u9645\u8bfb\u53d6\u7684\u5b57\u8282\u6570\u3002 \u7b2c\u4e09\u4e2a\u53c2\u6570\u662f\u4e0d\u5e26\u7b26\u53f7\u7684 size_t\uff0c\u4ee3\u8868\u6b64\u6b21\u5e0c\u671b\u8bfb\u53d6\u7684\u5b57\u8282\u6570\u3002<\/p>\n

\u663e\u7136 size_t \u7684\u6700\u5927\u503c\u662f ssize_t \u7684\u4e24\u500d\uff0c\u53ef\u4ee5\u5047\u8bbe size_t \u7684\u6700\u5927\u503c\u662f 255\uff0cssize_t \u7684\u6700\u5927\u503c\u662f 127\uff0c\u5982\u679c\u5728 read \u51fd\u6570\u7684\u7b2c\u4e09\u4e2a\u53c2\u6570\u4e2d\u586b 200\uff0c\u662f\u4e0d\u662f\u4ee3\u8868 read \u6700\u591a\u53ea\u80fd\u8bfb\u53d6 127 \u5b57\u8282\u6570\u636e\uff1f\u5982\u679c\u662f\u7684\u8bdd\uff0c\u611f\u89c9 linux \u8fd9\u4e48\u8bbe\u8ba1\u6709\u70b9\u4e0d\u5408\u7406\u554a\uff0c\u611f\u89c9\u548c\u6240\u89c1\u5373\u6240\u5f97\u539f\u5219\u6709\u70b9\u8fdd\u80cc\u3002<\/p>\n<\/p><\/div>\n

\u5927\u4f6c\u6709\u8a71\u8aaa<\/b> (15<\/span>) <\/div>\n
<\/div>\n<\/p><\/div>\n<\/p><\/div>\n
    \n
  • \n
    \n
    \n
    \u8cc7\u6df1\u5927\u4f6c : guyeu <\/span> <\/div>\n
    <\/i> <\/span> <\/div>\n<\/p><\/div>\n
    \u53ef\u80fd\u662f count \u4e0d\u5141\u8bb8\u5c0f\u4e8e 0\uff0c\u4f46\u662f\u8fd4\u56de\u503c\u6709\u53ef\u80fd\u5c0f\u4e8e 0\uff0c\u624d\u8fd9\u4e48\u8bbe\u8ba1 API \u5427 <\/div>\n<\/p><\/div>\n<\/li>\n
  • \n
    \n
    \n
    \u8cc7\u6df1\u5927\u4f6c : amaranthf <\/span> <\/div>\n
    <\/i> <\/span> <\/div>\n<\/p><\/div>\n
    \u6211\u89c9\u5f97\u5e94\u8be5\u662f\u6709\u4e24\u4e2a\u8003\u91cf\u5427\uff1a
    \u4e00\u662f\u8fd4\u56de\u7684\u65f6\u5019\u9700\u8981\u4e00\u4e2a\u503c\u7528\u6765\u8868\u793a\u201c\u9519\u8bef\u201d\uff0c\u800c 0 \u548c\u6b63\u6574\u6570\u90fd\u6709\u5176\u4ed6\u542b\u4e49\uff0c\u4e3a\u4e86\u907f\u514d\u518d\u589e\u52a0\u4e00\u4e2a\u53c2\u6570\uff0c\u5c31\u53ea\u80fd\u7528\u8d1f\u6570\u8868\u793a\u4e86\uff1b
    \u4e8c\u662f\u8bbe\u8ba1\u8005\u53ef\u80fd\u8ba4\u4e3a\u4f60\u6ca1\u6709\u4e00\u4e0b\u5b50\u8bfb\u51fa 2GB \u4ee5\u4e0a\u7684\u4e1c\u897f\u7684\u9700\u6c42\u2014\u2014\u5728 32 \u4f4d\u673a\u5668\u4e0a\u8fd9\u7684\u786e\u662f\u5f88\u96be\u7684\u4e8b\u60c5\uff0c\u800c 64 \u4f4d\u7684\u8bdd ssize_t \u4e5f\u8981\u53d8\u5927\uff0c\u5c31\u66f4\u4e0d\u53ef\u80fd\u4e86\u3002
    \u4e8b\u5b9e\u4e0a\u5728 Linux \u4e0b\u9762\uff0cread \u51fd\u6570\u5185\u90e8\u662f\u9650\u5236\u4e86\u4e00\u6b21\u8bfb\u53d6\u7684\u6700\u5927\u503c\u7684\uff0c\u8fd9\u4e2a\u503c\u662f 0x7ffff000 \uff08\u5305\u62ec 64 \u4f4d\u4e0b\u9762\uff09\u3002 <\/div>\n<\/p><\/div>\n<\/li>\n
  • \n
    \n
    \n
    \u8cc7\u6df1\u5927\u4f6c : CRVV <\/span> <\/div>\n
    <\/i> <\/span> <\/div>\n<\/p><\/div>\n
    read(2) \u91cc\u6709\u8bf4\uff0c
    On success, the number of bytes read is returned (zero indicates end of file)
    On error, -1 is returned, and errno is set appropriately.
    \u90a3\u4e48\u8fd4\u56de\u503c\u5fc5\u987b\u662f\u6709\u7b26\u53f7\u7684<\/p>\n

    \u53e6\u5916\uff0cread \u4e0d\u4fdd\u8bc1\u628a\u4f20\u8fdb\u53bb\u7684 buf \u8bfb\u6ee1\uff0c\u7ed9\u4e00\u4e2a\u957f\u5ea6 200 \u7684\uff0c\u53ea\u8bfb\u53d6 127 \u5b57\u8282\u6216\u8005\u53ea\u8bfb\u53d6 1 \u5b57\u8282\u90fd\u662f\u53ef\u4ee5\u7684\u3002<\/p>\n

    \u8fd9\u4e2a API \u4e5f\u4e0d\u662f Linux \u8bbe\u8ba1\u7684\uff0c\u8fd9\u662f POSIX \u91cc\u5b9a\u4e49\u7684 API\uff0cLinux \u53ea\u80fd\u7167\u7740\u5b9e\u73b0\u3002 <\/p><\/div>\n<\/p><\/div>\n<\/li>\n

  • \n
    \n
    \n
    \u8cc7\u6df1\u5927\u4f6c : momocraft <\/span> <\/div>\n
    <\/i> <\/span> <\/div>\n<\/p><\/div>\n
    “\u6240\u89c1\u5373\u6240\u5f97\u539f\u5219” \u662f\u4ec0\u4e48 <\/div>\n<\/p><\/div>\n<\/li>\n
  • \n
    \n
    \n
    \u8cc7\u6df1\u5927\u4f6c : leido <\/span> <\/div>\n
    <\/i> <\/span> <\/div>\n<\/p><\/div>\n
    \u4e0a\u53e4 API\uff0c\u80fd\u7528\u5c31\u884c <\/div>\n<\/p><\/div>\n<\/li>\n
  • \n
    \n
    \n
    \u8cc7\u6df1\u5927\u4f6c : AngryMagikarp <\/span> <\/div>\n
    <\/i> <\/span> <\/div>\n<\/p><\/div>\n
    \u9996\u5148 read \u672c\u6765\u5c31\u4e0d\u4fdd\u8bc1\u80fd\u8bfb\u53d6\u5230 count \u957f\u5ea6\u7684\u6570\u636e\uff0c\u4f60\u4f20\u518d\u5927\u7684 count\uff0c\u4ed6\u4e5f\u53ef\u4ee5\u8fd4\u56de\u4e00\u4e2a\u5b57\u8282\u7ed9\u4f60\u3002<\/p>\n

    \u5176\u6b21\uff0c\u54ea\u6015\u662f\u4e00\u6b21\u8bfb\u53d6\u6709\u7b26\u53f7\u6574\u6570\u6700\u5927\u503c\u7684\u6570\u636e\uff0c\u4e5f\u8db3\u591f\u4e86\u3002\u5373\u4f7f\u628a\u8fd4\u56de\u503c\u6362\u6210\u65e0\u7b26\u53f7\u6570\uff0c\u4f60\u4f9d\u7136\u53ef\u4ee5\u8bf4\uff0c\u4e00\u6b21\u6027\u6700\u591a\u8bfb\u53d6\u65e0\u7b26\u53f7\u6570\u7684\u6700\u5927\u503c\uff0c\u5b8c\u5168\u4e0d\u591f\u554a\uff0c\u6760\u7cbe\u5929\u4e0b\u7b2c\u4e00\u3002 <\/p><\/div>\n<\/p><\/div>\n<\/li>\n

  • \n
    \n
    \n
    \u8cc7\u6df1\u5927\u4f6c : AngryMagikarp <\/span> <\/div>\n
    <\/i> <\/span> <\/div>\n<\/p><\/div>\n
    According to POSIX.1, if count is greater than SSIZE_MAX, the result is implementation-defined; see NOTES for the upper limit on Linux.<\/p>\n

    On Linux, read() (and similar system calls) will transfer at most 0x7ffff000 (2,147,479,552) bytes, returning the number of bytes actually transferred. (This is true on both 32-bit and 64-bit systems.)<\/p>\n

    \u5728 Linux \u4e0a\uff0c\u5373\u4f7f 64 \u4f4d\u7cfb\u7edf\u4e2d\u4e5f\u6700\u591a\u4e00\u6b21\u6027\u8bfb\u53d6 2G \u6570\u636e\u3002\u53cd\u6b63\u6211\u8bfb\u53d6\u6587\u4ef6\u6216\u8005\u7f51\u7edc IO\uff0c\u4e00\u822c\u60c5\u51b5\u4e0b\u90fd\u662f 4096 \u8bfb\u3002 <\/p><\/div>\n<\/p><\/div>\n<\/li>\n

  • \n
    \n
    \n
    \u8cc7\u6df1\u5927\u4f6c : AngryMagikarp <\/span> <\/div>\n
    <\/i> <\/span> <\/div>\n<\/p><\/div>\n
    \u53e6\u5916\u4ec0\u4e48\u662f\u6240\u89c1\u5373\u6240\u5f97\u3002\u6211\u7528 linux \u8fd9\u4e48\u4e45\u4e86\uff0c\u65e9\u671f\u8fd8\u770b\u4e86\u5f88\u591a\u5173\u4e8e unix \u5386\u53f2\u548c\u8bbe\u8ba1\u7406\u5ff5\u7684\u4e66\uff0c\u4ece\u6765\u6ca1\u89c1\u8fc7\u6240\u89c1\u5373\u6240\u5f97\u8fd9\u4e2a\u6982\u5ff5\u3002\u6211\u53ea\u77e5\u9053\u5bcc\u6587\u672c\u7f16\u8f91\u5668\u6240\u89c1\u5373\u6240\u5f97\u3002 <\/div>\n<\/p><\/div>\n<\/li>\n
  • \n
    \n
    \n
    \u8cc7\u6df1\u5927\u4f6c : qakito <\/span> <\/div>\n
    <\/i> <\/span> <\/div>\n<\/p><\/div>\n
    1. \u5e38\u89c4\u573a\u666f\u4e2d\u4f7f\u7528\u5230\u7684 buffer \u8fdc\u5c0f\u4e8e SSIZE_MAX
    \u5982\u679c\u4f60\u7684\u4ee3\u7801\u91cc\u51fa\u73b0\u4e86\u4e00\u4e2a 4G \u5927\u5c0f\u7684 buffer\uff0c\u66f4\u5e94\u8be5\u5ba1\u89c6\u4ee3\u7801\u7684\u5408\u7406\u6027
    2. API \u53ea\u9700\u4fdd\u8bc1\u4f60\u7684 buffer \u4e0d\u6ea2\u51fa\uff0c\u4e0d\u4fdd\u8bc1\u4f60\u7684 buffer \u5168\u90e8\u585e\u6ee1 <\/div>\n<\/p><\/div>\n<\/li>\n
  • \n
    \n
    \n
    \u8cc7\u6df1\u5927\u4f6c : AngryMagikarp <\/span> <\/div>\n
    <\/i> <\/span> <\/div>\n<\/p><\/div>\n
    \u7cfb\u7edf\u8c03\u7528\u53ea\u662f\u63d0\u4f9b\u4e00\u4e9b\u57fa\u7840\u529f\u80fd\uff0c\u5e76\u4e0d\u662f\u4e3a\u4e86\u67d0\u4e9b\u7279\u5b9a\u573a\u666f\u8bbe\u8ba1\u7684\u3002\u5b9e\u9645\u4e2d\u5982\u679c\u771f\u7684\u8981\u4e00\u6b21\u6027\u8bfb\u53d6\u5927\u6570\u636e\uff0c\u4e5f\u53ef\u4ee5\u7b80\u5355\u5730\u5206\u591a\u6b21\u8bfb\u53d6\u5b9e\u73b0\u3002<\/p>\n

    Go \u8bed\u8a00\u4e2d ioutil.ReadAll \u51fd\u6570\u751a\u81f3\u662f\u6bcf\u6b21\u8bfb\u53d6 512 \u957f\u5ea6\uff0c\u901a\u8fc7\u5faa\u73af\u8bfb\u53d6\u5b9e\u73b0\u7684\u3002 <\/p><\/div>\n<\/p><\/div>\n<\/li>\n

  • \n
    \n
    \n
    \u8cc7\u6df1\u5927\u4f6c : nightwitch <\/span> <\/div>\n
    <\/i> <\/span> <\/div>\n<\/p><\/div>\n
    posix \u6807\u51c6\u8bde\u751f\u7684\u65f6\u5019\u786c\u4ef6\u89c4\u683c\u9650\u5236\u4e86\u4e0d\u53ef\u80fd\u4e00\u6b21\u6027\u8bfb\u6ee1 ssize_t \u7684
    Unix\/Linux \u6ca1\u6709\u6240\u89c1\u5373\u6240\u5f97\u8fd9\u4e2a\u539f\u5219 <\/div>\n<\/p><\/div>\n<\/li>\n
  • \n
    \n
    \n
    \u8cc7\u6df1\u5927\u4f6c : weyou <\/span> <\/div>\n
    <\/i> <\/span> <\/div>\n<\/p><\/div>\n
    \u8bfb\u53d6\u591a\u5c11\u5b57\u8282\u51fd\u6570\u81ea\u5df1\u80fd\u51b3\u5b9a\uff0c\u6240\u4ee5\u53ea\u8981\u51fd\u6570\u81ea\u5df1\u4fdd\u8bc1\u8fd4\u56de\u503c\u4e0d\u4f1a\u5f15\u8d77\u7b26\u53f7\u6ea2\u51fa\u5c31\u53ef\u4ee5\u4e86 <\/div>\n<\/p><\/div>\n<\/li>\n
  • \n
    \n
    \n
    \u4e3b<\/span> \u8cc7\u6df1\u5927\u4f6c : lolcat <\/span> <\/div>\n
    <\/i> <\/span> <\/div>\n<\/p><\/div>\n
    @AngryMagikarp \u6ca1\u770b\u61c2\u5e16\u5b50\u5427\uff0c\u6211\u8bf4\u5b9e\u9645\u8bfb\u53d6\u7684\u6700\u5927\u5b57\u8282\u6570\u53ea\u6709\u8ba1\u5212\u8bfb\u53d6\u7684\u6700\u5927\u5b57\u8282\u6570\u7684\u4e00\u534a\uff0c\u5c31\u50cf\u6211\u53ea\u80fd\u5403\u4e00\u7897\u996d\uff0c\u6211\u5374\u7528\u4e00\u4e2a\u76c6\u6253\u996d\uff0c\u6ca1\u60f3\u8868\u8fbe\u4e00\u6b21\u8bfb\u53d6\u7684\u5b57\u8282\u6570\u592a\u5c11\uff0c\u600e\u4e48\u5c31\u6760\u4e86\uff1f <\/div>\n<\/p><\/div>\n<\/li>\n
  • \n
    \n
    \n
    \u8cc7\u6df1\u5927\u4f6c : AngryMagikarp <\/span> <\/div>\n
    <\/i> <\/span> <\/div>\n<\/p><\/div>\n
    @lolcat \u8fd9\u91cc\u7684 count \u548c\u8fd4\u56de\u503c\u5e76\u6ca1\u6709\u5bf9\u5e94\u5173\u7cfb\uff0c\u4ed6\u4eec\u4e4b\u95f4\u7684\u552f\u4e00\u5173\u7cfb\u662f count \u5927\u4e8e\u7b49\u4e8e\u8fd4\u56de\u503c\uff0c\u90a3\u4e48 count \u6bd4\u8fd4\u56de\u503c\u5927\u591a\u5c11\u662f\u65e0\u6240\u8c13\u7684\u3002
    \u771f\u6b63\u548c count \u6709\u5173\u7cfb\u7684\u5176\u5b9e\u662f buf\uff0ccount \u8868\u793a\u7684\u5c31\u662f buf \u7684\u5927\u5c0f\uff0cbuf \u7684\u5927\u5c0f\u4e00\u5b9a\u4e0d\u4f1a\u662f\u8d1f\u7684\u3002\u800c\u4e14\u4f60\u53bb\u770b\u770b malloc \u7684\u53c2\u6570\u4e5f\u662f size_t\uff0c\u8fd9\u4e24\u8005\u662f\u7edf\u4e00\u7684\u3002 <\/div>\n<\/p><\/div>\n<\/li>\n
  • \n
    \n
    \n
    \u8cc7\u6df1\u5927\u4f6c : msg7086 <\/span> <\/div>\n
    <\/i> <\/span> <\/div>\n<\/p><\/div>\n
    C \u8bed\u8a00\u91cc\u7684\u6570\u503c\u5c31\u662f\u8fd9\u4e48\u8bbe\u8ba1\u7684\uff0c\u6709\u7b26\u53f7\u7684\u5c31\u662f\u65e0\u7b26\u53f7\u7684\u4e00\u534a\u3002
    \u4f60\u53ef\u4ee5\u7406\u89e3\u6210 count \u53ea\u80fd\u8f93\u5165 0-2147479552\uff0c\u800c\u8fd4\u56de\u503c\u53ea\u80fd\u662f-1-2147479552\uff0c\u8303\u56f4\u662f\u57fa\u672c\u4e00\u81f4\u7684\u3002<\/p>\n

    \u4f60\u8bf4
    \u300c\u53ef\u4ee5\u5047\u8bbe size_t \u7684\u6700\u5927\u503c\u662f 255\uff0cssize_t \u7684\u6700\u5927\u503c\u662f 127\uff0c\u5982\u679c\u5728 read \u51fd\u6570\u7684\u7b2c\u4e09\u4e2a\u53c2\u6570\u4e2d\u586b 200 \u300d
    \u800c\u5176\u5b9e read \u51fd\u6570\u89c4\u5b9a\u4f60\u53ea\u80fd\u586b 120\uff0c\u6240\u4ee5 255 \u4e5f\u597d 200 \u4e5f\u597d 127 \u4e5f\u597d\u90fd\u662f\u65e0\u5173\u7684\u3002<\/p>\n

    \u987a\u4fbf size_t \u5728 64 \u4f4d\u4e0b\u6700\u5927\u53ef\u4ee5\u53d6\u503c 18446744073709551615\uff0c\u5373\u4f7f\u8fd9\u6837\uff0cread \u4e5f\u53ea\u4f1a\u8bfb\u53d6 2147479552 \u5b57\u8282\u3002
    \u4f60\u7528\u4e00\u4e2a\u5b87\u5b99\u53bb\u6253\u996d\uff0c\u4e5f\u53ea\u7ed9\u4f60\u4e00\u5c0f\u7897\u3002 <\/div>\n<\/p><\/div>\n<\/li>\n

  • \n","protected":false},"excerpt":{"rendered":"

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