{"id":614,"date":"2009-03-31T13:32:11","date_gmt":"2009-03-31T04:32:11","guid":{"rendered":"http:\/\/blog.bitmeister.jp\/?p=614"},"modified":"2009-04-06T13:59:42","modified_gmt":"2009-04-06T04:59:42","slug":"%e3%81%84%e3%81%be%e3%81%95%e3%82%89c%e8%a8%80%e8%aa%9e%e3%81%aeextern%e3%81%a7%e6%82%a9%e3%82%80","status":"publish","type":"post","link":"https:\/\/blog.bitmeister.jp\/?p=614","title":{"rendered":"\u3044\u307e\u3055\u3089C\u8a00\u8a9e\u306eextern\u3067\u60a9\u3080"},"content":{"rendered":"<p>\u3068\u3042\u308b\u88fd\u54c1\u306e\u30bd\u30fc\u30b9\u30b3\u30fc\u30c9\u3092\u773a\u3081\u3066\u3044\u305f\u3068\u304d\u306b\u7591\u554f\u306b\u601d\u3063\u3066\u8abf\u3079\u305f\u3053\u3068\u3092\u30e1\u30e2\u3057\u307e\u3059\u3002<\/p>\n<p>C\u8a00\u8a9e\u3067\u901a\u5e38\u3001\u5927\u57df\u5909\u6570(\u30b0\u30ed\u30fc\u30d0\u30eb\u5909\u6570)\u3092\u8907\u6570\u306e\u30bd\u30fc\u30b9\u30d5\u30a1\u30a4\u30eb\u3067\u5171\u6709\u3059\u308b\u5834\u5408\u3001\u5171\u901a\u3067include\u3059\u308b\u30d8\u30c3\u30c0\u30d5\u30a1\u30a4\u30eb\u306bextern int abc;\u307f\u305f\u3044\u306b\u66f8\u3044\u3066\u3001\u30bd\u30fc\u30b9\u30d5\u30a1\u30a4\u30eb\u306e\u3044\u305a\u308c\u304b\uff11\u3064\u306b\u5b9f\u4f53\u3092int abc;\u307f\u305f\u3044\u306b\u66f8\u304f\u3068\uff08\u79c1\u306f\uff09\u601d\u3063\u3066\u3044\u305f\u306e\u3067\u3059\u304c\u3001\u305d\u306e\u88fd\u54c1\u306e\u30bd\u30fc\u30b9\u3067\u306f\u30d8\u30c3\u30c0\u30d5\u30a1\u30a4\u30eb\u306e\u65b9\u306bint abc;\u3068\u3042\u308a\u3001\u5404\u30bd\u30fc\u30b9\u30d5\u30a1\u30a4\u30eb\u306bextern int abc;\u3068\u3044\u3046\u98a8\u306b\u66f8\u304b\u308c\u3066\u3044\u307e\u3059\u3002<br \/>\n<!--more--><br \/>\n\u4e00\u77ac\u3001\u305d\u308c\u305e\u308c\u306e\u30e2\u30b8\u30e5\u30fc\u30eb\uff08\u30bd\u30fc\u30b9\u30d5\u30a1\u30a4\u30eb\uff09\u306b\u5225\u3005\u306e\u5b9f\u4f53\u304c\u5b58\u5728\u3059\u308b\u306e\u304b\u306a\u3001\u3068\u601d\u3063\u305f\u306e\u3067\u3059\u304c\u3001\u5b9f\u969b\u306e\u305d\u306e\u88fd\u54c1\u306e\u52d5\u304d\u3092\u898b\u3066\u307f\u308b\u3068\u3061\u3083\u3093\u3068\u5909\u6570\u3092\u5171\u6709\u3057\u3066\u4f7f\u3063\u3066\u3044\u308b\u3088\u3046\u3067\u3059\u3002<br \/>\n\u79c1\u306e\u3044\u307e\u307e\u3067\u306e\u7406\u89e3\u304c\u9593\u9055\u3063\u3066\u3044\u308b\u304b\u3082\u3057\u308c\u306a\u3044\u306e\u3067\u8abf\u3079\u3088\u3046\u3068\u601d\u3063\u305f\u306e\u3067\u3059\u304c\u3001C\u8a00\u8a9e\u306e\u898f\u7d04\u3092\u8abf\u3079\u308b\u306e\u3082\u5104\u52ab\u3060\u3057\u3001\u74b0\u5883\u4f9d\u5b58\u304b\u3082\u3057\u308c\u306a\u3044\u306e\u3067\u3001\u3068\u308a\u3042\u3048\u305a\u30b5\u30f3\u30d7\u30eb\u3092\u66f8\u3044\u3066\u624b\u5143\u306eUbuntu\u306egcc(4.2.4)\u3067\u6319\u52d5\u3092\u8abf\u3079\u3066\u307f\u307e\u3057\u305f\u3002<\/p>\n<p>\u6b21\u306e\u3088\u3046\u306a2\u3064\u306e\u30bd\u30fc\u30b9\u30d5\u30a1\u30a4\u30eb\u3092\u7528\u610f\u3057\u3001\u30b3\u30f3\u30d1\u30a4\u30eb\u3057\u3066\u5b9f\u884c\u3057\u3066\u307f\u307e\u3057\u305f\u3002<br \/>\n\uff08\u30d8\u30c3\u30c0\u30d5\u30a1\u30a4\u30eb\u306f\u4f5c\u3089\u305a\u306b\u305d\u308c\u305e\u308c\u306e\u30bd\u30fc\u30b9\u306b\u540c\u3058\u5909\u6570\u5ba3\u8a00\u3092\u66f8\u304d\u307e\u3057\u305f\u3002\uff09<\/p>\n<p>\u30bd\u30fc\u30b9\u305d\u306e\uff11(a.c)<\/p>\n<pre style=\"margin:0 1em;padding:1ex 2ex;background-color:#f0f0f0;border:solid 1px gray\">\r\n#include &lt;stdio.h>\r\n\r\nint value;\r\n\r\nextern int value;\r\n\r\nextern void b(void);\r\n\r\nint main()\r\n{\r\n        value = 1;\r\n\r\n        b();\r\n\r\n        printf(\"a:value=%d\\n\",value);\r\n        return 0;\r\n}\r\n<\/pre>\n<p>\n\u30bd\u30fc\u30b9\u305d\u306e\uff12(b.c)<\/p>\n<pre style=\"margin:0 1em;padding:1ex 2ex;background-color:#f0f0f0;border:solid 1px gray\">\r\n#include &lt;stdio.h>\r\n\r\nint value;\r\n\r\nextern int value;\r\n\r\nvoid b(void)\r\n{\r\n        printf(\"b:value=%d\\n\",value++);\r\n}\r\n<\/pre>\n<p>\u5b9f\u884c\u7d50\u679c<\/p>\n<pre style=\"margin:0 1em;padding:1ex 2ex;color:white;background-color:#000000;border:solid 1px gray\">\r\nubuntu:~\/test\/extern$ .\/a.out\r\nb:value=1\r\na:value=2\r\n<\/pre>\n<p>\u3061\u3083\u3093\u3068\u5171\u6709\u3055\u308c\u3066\u3044\u307e\u3059\u3002<\/p>\n<pre style=\"margin:0 1em;padding:1ex 2ex;background-color:#f0f0f0;border:solid 1px gray\">\r\nint value;\r\n\r\nextern int value;\r\n<\/pre>\n<p>\u306e\u3068\u3053\u308d\u3092\u3001extern\u306e\u307f\u306b\u3057\u305f\u308a\u3001extern\u306e\u65b9\u3092\u5916\u3057\u305f\u308a\u3057\u3066\u307f\u3066\u5171\u6709\u3055\u308c\u308b\u304b\u78ba\u8a8d\u3057\u305f\u7d50\u679c\u306f\u4ee5\u4e0b\u306e\u3068\u304a\u308a\u3002<\/p>\n<table border=\"1\" align=\"center\">\n<tr>\n<th colspan=\"2\">\u30bd\u30fc\u30b9\u30d5\u30a1\u30a4\u30eb<\/th>\n<th rowspan=\"2\">\u6319\u52d5<\/th>\n<\/tr>\n<tr>\n<td align=\"center\">a.c<\/td>\n<td align=\"center\">b.c<\/td>\n<\/tr>\n<tr>\n<td>extern\u306a\u3057<\/td>\n<td>extern\u306a\u3057<\/td>\n<td>\u5171\u6709\u3055\u308c\u308b<\/td>\n<\/tr>\n<tr>\n<td>extern\u306e\u307f<\/td>\n<td>extern\u306e\u307f<\/td>\n<td>\u30b3\u30f3\u30d1\u30a4\u30eb\uff08\u30ea\u30f3\u30af\uff09\u30a8\u30e9\u30fc<\/td>\n<\/tr>\n<tr>\n<td>extern\u306a\u3057<\/td>\n<td>extern\u306e\u307f<\/td>\n<td>\u5171\u6709\u3055\u308c\u308b<\/td>\n<\/tr>\n<tr>\n<td>extern\u306e\u307f<\/td>\n<td>extern\u306a\u3057<\/td>\n<td>\u5171\u6709\u3055\u308c\u308b<\/td>\n<\/tr>\n<\/table>\n<p>\u5927\u57df\u5909\u6570\u306f\u6697\u9ed9\u3067static\u306b\u306f\u306a\u3089\u306a\u3044\u306e\u3067\u3001\u3084\u306f\u308a\u3001\u30b3\u30f3\u30d1\u30a4\u30eb\u304c\u901a\u308c\u3070\u5171\u6709\u3055\u308c\u307e\u3059\u306d\u3002\uff08\u3088\u304f\u8003\u3048\u308c\u3070\u5f53\u305f\u308a\u524d\u3067\u3059\u304c\u3002\uff09<br \/>\n\u3061\u306a\u307f\u306b\u3001a.c\u3068b.c\u306e\u4e21\u65b9\u3067\u3001int value=0;\u306e\u3088\u3046\u306b\u521d\u671f\u5316\u3059\u308b\u3068\u30b3\u30f3\u30d1\u30a4\u30eb\uff08\u30ea\u30f3\u30af\uff09\u30a8\u30e9\u30fc\u3068\u306a\u308a\u307e\u3059\u3002<\/p>\n<pre style=\"margin:0 1em;padding:1ex 2ex;color:white;background-color:#000000;border:solid 1px gray\">\r\nubuntu:~\/test\/extern$ gcc a.c b.c\r\n\/tmp\/ccuqLUhV.o:(.bss+0x0): multiple definition of `value'\r\n\/tmp\/cce2atrh.o:(.data+0x0): first defined here\r\n<\/pre>\n<p>\u7247\u65b9\uff08\uff11\u3064\uff09\u306e\u307f\u521d\u671f\u5316\u3059\u308b\u5834\u5408\u306f\u30a8\u30e9\u30fc\u306b\u306f\u306a\u308a\u307e\u305b\u3093\u3002<\/p>\n<p>\u3053\u308c\u3089\u306e\u7d50\u679c\u304b\u3089\u30b3\u30f3\u30d1\u30a4\u30e9\u3068\u304b\u30ea\u30f3\u30ab\u306e\u6319\u52d5\u3092\u60f3\u50cf\u3059\u308b\u3068\u3001<br \/>\nextern\u306e\u3064\u3044\u305f\u5927\u57df\u5909\u6570\u306f\u5fc5\u305a\u3044\u305a\u308c\u304b\u306e\u30e2\u30b8\u30e5\u30fc\u30eb\u306b\u5b9f\u4f53\u304c\u306a\u3044\u3068\u30c0\u30e1\u3067\u3001extern\u306e\u3064\u304b\u306a\u3044\u5927\u57df\u5909\u6570\u306f\u57fa\u672c\u7684\u306bextern\u3042\u308a\u3068\u540c\u3058\u3060\u304c\u3001\u3044\u305a\u308c\u306e\u30e2\u30b8\u30e5\u30fc\u30eb\u306b\u3082\u5b9f\u4f53\u304c\u306a\u3051\u308c\u3070\u30ea\u30f3\u30ab\u304c\u5b9f\u4f53\u3092\u4f5c\u308b\u3001<br \/>\n\u3068\u3044\u3046\u611f\u3058\u306b\u306a\u308b\u3067\u3057\u3087\u3046\u304b\u3002<br \/>\n\uff08\u3042\u3068\u3001\u521d\u671f\u5316\u3092\u3057\u305f\u3089\u5fc5\u305a\u305d\u306e\u30e2\u30b8\u30e5\u30fc\u30eb\u306b\u5b9f\u4f53\u304c\u4f5c\u3089\u308c\u3001\u8907\u6570\u306e\u30e2\u30b8\u30e5\u30fc\u30eb\u306b\u5b9f\u4f53\u304c\u3042\u308c\u3070\u30a8\u30e9\u30fc\u3068\u306a\u308b\u3002\uff09<\/p>\n<p>\u3067\u3001\u3053\u3053\u3067\u7591\u554f\u306b\u601d\u3063\u305f\u306e\u3067\u3059\u304c\u3001\u610f\u56f3\u7684\u306b\u5171\u6709\u3059\u308b\u5834\u5408\u306fextern\u306a\u3057\u3067\u3082\u3044\u3044\u3068\u601d\u3046\u306e\u3067\u3059\u304c\u3001\u305d\u308c\u3067\u306f\u305f\u307e\u305f\u307e\u4ed6\u306e\u30e2\u30b8\u30e5\u30fc\u30eb\u306b\u3042\u308b\u3082\u306e\u3068\u540c\u3058\uff08\u5927\u57df\uff09\u5909\u6570\u540d\u3092\u4f7f\u3063\u3066\u3044\u305f\u3089\u3001\u610f\u56f3\u305b\u305a\u306b\u5171\u6709\u3055\u308c\u3066\u3057\u307e\u3046\u3001\u3068\u3044\u3046\u3053\u3068\u306b\u306a\u308a\u307e\u3059\u3002<br \/>\n\u305d\u3046\u3044\u3046\u72b6\u6cc1\u306b\u306a\u3063\u305f\u3089\u3001\u304b\u306a\u308a\u898b\u3064\u3051\u306b\u304f\u3044\u30d0\u30b0\u306b\u306a\u308a\u305d\u3046\u3067\u3059\u306d\u3002<br \/>\n\uff08extern\u3068\u304bstatic\u3068\u304b\u660e\u793a\u3059\u308b\u7fd2\u6163\u3092\u3064\u3051\u3066\u304a\u3051\u3070\u8d77\u3053\u308a\u306b\u304f\u3044\u554f\u984c\u3067\u3059\u304c\u3002\uff09<\/p>\n<p>\u3068\u3044\u3046\u308f\u3051\u3067\u3001\u305d\u3046\u3057\u305f\u554f\u984c\u3092\u672a\u7136\u306b\u9632\u3050\u30b3\u30f3\u30d1\u30a4\u30eb\uff08\u30ea\u30f3\u30ab\uff09\u30aa\u30d7\u30b7\u30e7\u30f3\u3092\u8abf\u3079\u3066\u304a\u304d\u307e\u3057\u305f\u3002<br \/>\n\uff08\u3053\u306e\u30aa\u30d7\u30b7\u30e7\u30f3\u3001\u30c7\u30d5\u30a9\u30eb\u30c8\u3067\u306f\u7121\u52b9\u306e\u3088\u3046\u3067\u3059\u3002\uff09<\/p>\n<pre style=\"margin:0 1em;padding:1ex 2ex;color:white;background-color:#000000;border:solid 1px gray\">\r\nubuntu:~\/test\/extern$ gcc a.c b.c -Xlinker --warn-common\r\n\/tmp\/ccu1WiL1.o: warning: multiple common of `value'\r\n\/tmp\/ccsffaYm.o: warning: previous common is here\r\n<\/pre>\n<p>extern\u306e\u3064\u304b\u306a\u3044\u540c\u3058\u540d\u524d\u306e\u5927\u57df\u5909\u6570\u3092\u8907\u6570\u306e\u30e2\u30b8\u30e5\u30fc\u30eb\u3067\u5ba3\u8a00\u3059\u308b\u3068\u3053\u306e\u3088\u3046\u306bwarning\u304c\u51fa\u307e\u3059\u3002<\/p>\n<p>\u3082\u3046\uff11\u30d1\u30bf\u30fc\u30f3\u3042\u308a\u307e\u3059\u3002<\/p>\n<pre style=\"margin:0 1em;padding:1ex 2ex;color:white;background-color:#000000;border:solid 1px gray\">\r\nubuntu:~\/test\/extern$ gcc a.c b.c -fno-common\r\n\/tmp\/cc1Pz9uE.o:(.bss+0x0): multiple definition of `value'\r\n\/tmp\/cckai0mp.o:(.bss+0x0): first defined here\r\n<\/pre>\n<p>\u3053\u3061\u3089\u306f\u30b3\u30f3\u30d1\u30a4\u30eb\uff08\u30ea\u30f3\u30af\uff09\u30a8\u30e9\u30fc\u3068\u306a\u308a\u307e\u3059\u3002<\/p>\n<p>\u4ee5\u4e0a\u3001\u77e5\u3063\u3066\u3044\u308b\u3088\u3046\u3067\u77e5\u3089\u306a\u3044\uff08\u306e\u306f\u79c1\u3060\u3051\uff1f\uff09\u3001C\u8a00\u8a9e\u306b\u307e\u3064\u308f\u308b\u5c0f\u30cd\u30bf\u3067\u3057\u305f\u3002<\/p>\n<p>\uff03\u4eca\u691c\u7d22\u3057\u305f\u3089\u3001\u540c\u3058\u3053\u3068\u306b\u60a9\u3093\u3060\u65b9\u304c<a href=\"http:\/\/d.hatena.ne.jp\/pneumaster\/20080423\">\u4ed6\u306b\u3082\u3044\u305f<\/a>\u3088\u3046\u3067\u3059\u3002<\/p>\n","protected":false},"excerpt":{"rendered":"<p>\u3068\u3042\u308b\u88fd\u54c1\u306e\u30bd\u30fc\u30b9\u30b3\u30fc\u30c9\u3092\u773a\u3081\u3066\u3044\u305f\u3068\u304d\u306b\u7591\u554f\u306b\u601d\u3063\u3066\u8abf\u3079\u305f\u3053\u3068\u3092\u30e1\u30e2\u3057\u307e\u3059\u3002 C\u8a00\u8a9e\u3067\u901a\u5e38\u3001\u5927\u57df\u5909\u6570(\u30b0\u30ed\u30fc\u30d0\u30eb\u5909\u6570)\u3092\u8907\u6570\u306e\u30bd\u30fc\u30b9\u30d5\u30a1\u30a4\u30eb\u3067\u5171\u6709\u3059\u308b\u5834\u5408\u3001\u5171\u901a\u3067include\u3059\u308b\u30d8\u30c3\u30c0\u30d5\u30a1\u30a4\u30eb\u306bextern int  [&hellip;]<\/p>\n","protected":false},"author":7,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[17],"tags":[40],"class_list":["post-614","post","type-post","status-publish","format-standard","hentry","category-tech","tag-40"],"_links":{"self":[{"href":"https:\/\/blog.bitmeister.jp\/index.php?rest_route=\/wp\/v2\/posts\/614","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/blog.bitmeister.jp\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/blog.bitmeister.jp\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/blog.bitmeister.jp\/index.php?rest_route=\/wp\/v2\/users\/7"}],"replies":[{"embeddable":true,"href":"https:\/\/blog.bitmeister.jp\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=614"}],"version-history":[{"count":4,"href":"https:\/\/blog.bitmeister.jp\/index.php?rest_route=\/wp\/v2\/posts\/614\/revisions"}],"predecessor-version":[{"id":630,"href":"https:\/\/blog.bitmeister.jp\/index.php?rest_route=\/wp\/v2\/posts\/614\/revisions\/630"}],"wp:attachment":[{"href":"https:\/\/blog.bitmeister.jp\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=614"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/blog.bitmeister.jp\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=614"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/blog.bitmeister.jp\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=614"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}