{"id":2859,"date":"2016-09-18T13:13:58","date_gmt":"2016-09-18T05:13:58","guid":{"rendered":"http:\/\/ixyzero.com\/blog\/?p=2859"},"modified":"2016-09-18T13:13:58","modified_gmt":"2016-09-18T05:13:58","slug":"c%e8%af%ad%e8%a8%80%e4%b8%ad%e7%9a%84%e6%96%87%e4%bb%b6%e3%80%81%e5%ad%97%e7%ac%a6%e4%b8%b2%e6%93%8d%e4%bd%9c","status":"publish","type":"post","link":"https:\/\/ixyzero.com\/blog\/archives\/2859.html","title":{"rendered":"C\u8bed\u8a00\u4e2d\u7684\u6587\u4ef6\u3001\u5b57\u7b26\u4e32\u64cd\u4f5c"},"content":{"rendered":"<p>=Start=<\/p>\n<h5>\u7f18\u7531\uff1a<\/h5>\n<p>\u6700\u8fd1\u5728Linux\u73af\u5883\u4e0b\u7528C\u8bed\u8a00\u5b9e\u73b0\u4e00\u4e9b\u529f\u80fd\uff0c\u5728\u5b8c\u6210\u5de5\u4f5c\u4efb\u52a1\u7684\u540c\u65f6\u5b66\u4e60\u3001\u6536\u85cf\u4e86\u4e00\u4e9b\u7ecf\u5178\u7684\u4ee3\u7801\u7247\u6bb5\/\u94fe\u63a5\uff0c\u60f3\u5230\u4ee5\u540e\u53ef\u80fd\u4f1a\u7528\u5230\uff0c\u6240\u4ee5\u5728\u529f\u80fd\u5b9e\u73b0\u4e4b\u540e\u53c8\u91cd\u65b0\u68b3\u7406\u4e86\u4e00\u4e0b\u76f8\u5173\u5185\u5bb9\u5e76\u6574\u7406\u81f3\u6b64\uff0c\u65b9\u4fbf\u4ee5\u540e\u78b0\u5230\u7c7b\u4f3c\u9700\u6c42\u7684\u65f6\u5019\u80fd\u5feb\u901f\u4e0a\u624b\u3002<\/p>\n<h5>\u6b63\u6587\uff1a<\/h5>\n<h6>1.\u7528getline\u51fd\u6570\u5faa\u73af\u8bfb\u53d6\u6587\u4ef6\u5185\u5bb9<\/h6>\n<pre class=\"lang:default decode:true \">#define _GNU_SOURCE\n#include &lt;stdio.h&gt;\n#include &lt;stdlib.h&gt;\n\nint main(void) {\n    FILE *fp;\n    char *line = NULL;\n    size_t len = 0;\n    ssize_t read;\n\n   fp = fopen(\"\/etc\/motd\", \"r\");\n    if (fp == NULL)\n        exit(EXIT_FAILURE);\n\n   while ((read = getline(&amp;line, &amp;len, fp)) != -1) {\n        printf(\"Retrieved line of length %zu :'%s'\\n\", read, line); \/* \u5728line\u4e2d\u5305\u542b\u4e86\u4e00\u4e2a\u6362\u884c\u7b26'\\n'*\/\n    }\n\n   free(line);\n   exit(EXIT_SUCCESS);\n}<\/pre>\n<p>\u53e6\u5916\u8fd8\u6709fgets\u51fd\u6570\uff0c\u4e00\u822c\u7528\u4e8e\u56fa\u5b9a\u683c\u5f0f(\u6bcf\u884c\u957f\u5ea6)\u6587\u4ef6\u7684\u8bfb\u53d6\uff0c\u4f60\u53ef\u4ee5\u6839\u636e\u5177\u4f53\u60c5\u51b5\u51b3\u5b9a\u662f\u5426\u9009\u7528\uff1a<\/p>\n<pre class=\"lang:default decode:true\">#include &lt;stdio.h&gt;\n#include &lt;stdlib.h&gt;\n\nint main (void) {\n    char buf[256];\n    while (fgets (buf, sizeof(buf), stdin)) {\n        printf(\"line: %s\", buf);\n    }\n    if (ferror(stdin)) {\n        fprintf(stderr,\"Oops, error reading stdin\\n\");\n        abort();\n    }\n    return 0;\n}<\/pre>\n<ul>\n<li><a href=\"http:\/\/stackoverflow.com\/questions\/13555097\/linux-c-read-file-line-by-line\">http:\/\/stackoverflow.com\/questions\/13555097\/linux-c-read-file-line-by-line<\/a><\/li>\n<li><a href=\"http:\/\/stackoverflow.com\/questions\/3501338\/c-read-file-line-by-line\">http:\/\/stackoverflow.com\/questions\/3501338\/c-read-file-line-by-line<\/a><\/li>\n<li><a href=\"http:\/\/linux.die.net\/man\/3\/getline\">http:\/\/linux.die.net\/man\/3\/getline<\/a><\/li>\n<li><a href=\"http:\/\/rosettacode.org\/wiki\/Read_a_file_line_by_line#C\">http:\/\/rosettacode.org\/wiki\/Read_a_file_line_by_line#C<\/a><\/li>\n<\/ul>\n<h6>2.\u5982\u4f55\u5224\u65ad\u5b57\u7b26\u4e32\u6307\u9488\u4e3a\u7a7a\/\u6307\u5411\u7684\u5185\u5bb9\u4e3a\u7a7a<\/h6>\n<p>\u9996\u5148\u68c0\u67e5\u8be5\u5b57\u7b26\u4e32\u6307\u9488\u662f\u5426\u4e3aNULL\uff0c\u7136\u540e\u770b\u8be5\u5b57\u7b26\u4e32\u6307\u9488\u6307\u5411\u5185\u5bb9\u7684\u7b2c\u4e00\u4e2a\u5b57\u7b26\u662f\u5426\u4e3a\u300c\\0\u300d\u6765\u8fdb\u884c\u5224\u65ad\uff1a<\/p>\n<pre class=\"lang:default decode:true \">char *c = \"\";\nif ((c != NULL) &amp;&amp; (c[0] == '\\0')) {\n    printf(\"c is empty\\n\");\n}<\/pre>\n<ul>\n<li><a href=\"http:\/\/stackoverflow.com\/questions\/7970617\/how-can-i-check-if-char-variable-points-to-empty-string\">http:\/\/stackoverflow.com\/questions\/7970617\/how-can-i-check-if-char-variable-points-to-empty-string<\/a><\/li>\n<\/ul>\n<h6>3.\u7528sscanf\u51fd\u6570\u8fdb\u884c\u5b57\u7b26\u4e32\u622a\u53d6<\/h6>\n<pre class=\"lang:default decode:true \">#include &lt;stdio.h&gt;\n#include &lt;string.h&gt;\n#include &lt;stdlib.h&gt;\n\nint main() {\n    char src_ip[16];\n    char * ssh_client = NULL;\n    if ((getenv (\"SSH_CLIENT\"))) {\n        ssh_client = getenv (\"SSH_CLIENT\");\n        printf(\"SSH_CLIENT = %s\\n\", ssh_client);\n    }\n\n    if ( ssh_client != NULL ) {\n        printf(\"SSH_CLIENT = %s\\n\", ssh_client);\n        sscanf(ssh_client, \"%15[^ ]\", src_ip);  \/\/ \u53d6 ssh_client \u53d8\u91cf\u6307\u5411\u7684\u5b57\u7b26\u4e32\u4e2d\u4ece\u5f00\u5934\u5230\u7b2c\u4e00\u4e2a\u7a7a\u767d\u5b57\u7b26\u4e4b\u95f4\u7684\u6700\u591a15\u4e2a\u5b57\u7b26\u5b58\u5165 src_ip \u53d8\u91cf\u4e2d\n        printf(\"SRC_IP\\t= %s\\n\", src_ip);\n    } else {\n        printf(\"SSH_CLIENT = null\\n\");\n    }\n    return 0;\n}<\/pre>\n<ul>\n<li><a href=\"http:\/\/stackoverflow.com\/questions\/3478636\/extract-a-substring-in-c\">http:\/\/stackoverflow.com\/questions\/3478636\/extract-a-substring-in-c<\/a><\/li>\n<li><a href=\"https:\/\/linux.die.net\/man\/3\/sscanf\">https:\/\/linux.die.net\/man\/3\/sscanf<\/a><\/li>\n<li><a href=\"http:\/\/stackoverflow.com\/questions\/4214314\/get-a-substring-of-a-char\">http:\/\/stackoverflow.com\/questions\/4214314\/get-a-substring-of-a-char<\/a><\/li>\n<li><a href=\"http:\/\/stackoverflow.com\/questions\/2114377\/strings-in-c-how-to-get-substring\">http:\/\/stackoverflow.com\/questions\/2114377\/strings-in-c-how-to-get-substring<\/a><\/li>\n<li><a href=\"http:\/\/randu.org\/tutorials\/c\/strings.php\">http:\/\/randu.org\/tutorials\/c\/strings.php<\/a><\/li>\n<\/ul>\n<h6>4.\u7528strncpy\u51fd\u6570\u8fdb\u884c\u5b57\u7b26\u4e32\u590d\u5236<\/h6>\n<pre class=\"lang:default decode:true \">#include &lt;stdio.h&gt;\n#include &lt;string.h&gt;\n#include &lt;stdlib.h&gt;\n\nint main(){\n    char * ssh_client = (char *)NULL;\n    char src_ip[16] = \"\";\n    if ( ssh_client != NULL ) {\n        sscanf(ssh_client, \"%15[^ ]\", src_ip);\n    } else {\n        \/\/ src_ip = \"null\";\n        strncpy(src_ip, \"null\", 15);\/\/\u8fd9\u91cc\u9700\u8981\u7528strncpy\u51fd\u6570\u8fdb\u884c\u5b57\u7b26\u4e32\u6570\u7ec4\u8d4b\u503c\uff0c\u4e0a\u9762\u90a3\u884c\u7684\u64cd\u4f5c\u662f\u9519\u8bef\u7684\uff01\n    }\n    printf(\"src_ip = %s\\n\", src_ip);\n    return 0;\n}<\/pre>\n<h6>5.\u5c06 \u5b57\u7b26\u4e32\u6307\u9488 \u8f6c\u6362\u6210 \u5b57\u7b26\u4e32\u6570\u7ec4<\/h6>\n<ul>\n<li><a href=\"http:\/\/stackoverflow.com\/questions\/1508838\/how-to-copy-char-str-to-char-c-in-c\">http:\/\/stackoverflow.com\/questions\/1508838\/how-to-copy-char-str-to-char-c-in-c<\/a><\/li>\n<li><a href=\"http:\/\/stackoverflow.com\/questions\/13553752\/convert-char-pointer-to-unsigned-char-array\">http:\/\/stackoverflow.com\/questions\/13553752\/convert-char-pointer-to-unsigned-char-array<\/a><\/li>\n<\/ul>\n<h6>6.\u5c06 \u5b57\u7b26\u4e32\u6570\u7ec4 \u8f6c\u6362\u6210 \u5b57\u7b26\u4e32\u6307\u9488<\/h6>\n<ul>\n<li><a href=\"http:\/\/stackoverflow.com\/questions\/9627962\/is-it-possible-to-convert-char-to-char-in-c\">http:\/\/stackoverflow.com\/questions\/9627962\/is-it-possible-to-convert-char-to-char-in-c<\/a><\/li>\n<\/ul>\n<h6>7.\u5b57\u7b26\u4e32\u6570\u7ec4\u7684\u521d\u59cb\u5316<\/h6>\n<ul>\n<li><a href=\"http:\/\/stackoverflow.com\/questions\/18688971\/c-char-array-initialization\">http:\/\/stackoverflow.com\/questions\/18688971\/c-char-array-initialization<\/a><\/li>\n<li><a href=\"http:\/\/stackoverflow.com\/questions\/963911\/how-to-initialize-char-array-from-a-string\">http:\/\/stackoverflow.com\/questions\/963911\/how-to-initialize-char-array-from-a-string<\/a><\/li>\n<\/ul>\n<p>\u2026\u2026\u4e0d\u5b9a\u671f\u66f4\u65b0\u2026\u2026<\/p>\n<p>=END=<\/p>\n","protected":false},"excerpt":{"rendered":"<p>=Start= \u7f18\u7531\uff1a \u6700\u8fd1\u5728Linux\u73af\u5883\u4e0b\u7528C\u8bed\u8a00\u5b9e\u73b0\u4e00\u4e9b\u529f\u80fd\uff0c\u5728\u5b8c\u6210\u5de5\u4f5c\u4efb\u52a1\u7684\u540c\u65f6\u5b66\u4e60\u3001\u6536\u85cf\u4e86\u4e00\u4e9b\u7ecf\u5178\u7684 [&hellip;]<\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[23,11,7],"tags":[100,30],"class_list":["post-2859","post","type-post","status-publish","format-standard","hentry","category-knowledgebase-2","category-linux","category-programing","tag-c","tag-linux"],"views":5830,"_links":{"self":[{"href":"https:\/\/ixyzero.com\/blog\/wp-json\/wp\/v2\/posts\/2859","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/ixyzero.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/ixyzero.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/ixyzero.com\/blog\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/ixyzero.com\/blog\/wp-json\/wp\/v2\/comments?post=2859"}],"version-history":[{"count":0,"href":"https:\/\/ixyzero.com\/blog\/wp-json\/wp\/v2\/posts\/2859\/revisions"}],"wp:attachment":[{"href":"https:\/\/ixyzero.com\/blog\/wp-json\/wp\/v2\/media?parent=2859"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/ixyzero.com\/blog\/wp-json\/wp\/v2\/categories?post=2859"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/ixyzero.com\/blog\/wp-json\/wp\/v2\/tags?post=2859"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}