{"id":3886,"date":"2019-12-14T00:01:49","date_gmt":"2019-12-14T08:01:49","guid":{"rendered":"https:\/\/c-for-dummies.com\/blog\/?p=3886"},"modified":"2019-12-07T10:01:20","modified_gmt":"2019-12-07T18:01:20","slug":"my-own-strlcpy-function","status":"publish","type":"post","link":"https:\/\/c-for-dummies.com\/blog\/?p=3886","title":{"rendered":"My Own strlcpy()<\/em> Function"},"content":{"rendered":"

Armed with information about how the non-standard strlcpy()<\/em> function is implemented by my compiler (see last week’s Lesson<\/a>), and fully testing its input and output, I was better able to craft my own version. Granted, it’s not the way I would have coded things on my own, but the point is to recreate the function exactly so it can be used as a substitute.
\n
\nHere is my reverse-engineered solution to the strlcpy()<\/em> function, which includes the main()<\/em> and test()<\/em> functions from last week’s sample code:<\/p>\n

\r\n#include <stdio.h>\r\n\r\nsize_t strlcpy(char *restrict dst, const char *restrict src, size_t dstsize)\r\n{\r\n    int offset;\r\n\r\n    \/* duplicate the string up to dstsize *\/<\/span>\r\n    offset = 0;\r\n        \/* guard against silly dstsize values *\/<\/span>\r\n    if( dstsize > 0 )\r\n    {\r\n        while( *(src+offset) != '\\0' )\r\n        {\r\n            \/* bail if dstsize is met *\/<\/span>\r\n            if( offset==dstsize )\r\n            {\r\n                offset--;\r\n                break;\r\n            }\r\n\r\n            \/* duplicate the string *\/<\/span>\r\n            *(dst+offset) = *(src+offset);\r\n            offset++;\r\n        }\r\n    }\r\n    \/* always remember to cap a created string! *\/<\/span>\r\n    *(dst+offset) = '\\0';\r\n    \r\n    \/* return the string length of src *\/<\/span>\r\n    while( *(src+offset) != '\\0' )\r\n        offset++;\r\n\r\n    return(offset);\r\n}\r\n\r\nvoid test(int size)\r\n{\r\n    char string[] = \"Hello there, Venus\";\r\n    char buffer[19];\r\n    int r;\r\n\r\n    r = strlcpy(buffer,string,size);\r\n\r\n    printf(\"Copied '%s' into '%s', length %d\\n\",\r\n            string,\r\n            buffer,\r\n            r\r\n          );\r\n}\r\n\r\nint main()\r\n{\r\n    test(19);\r\n    test(10);\r\n    test(1);\r\n    test(0);\r\n\r\n    return(0);\r\n}<\/pre>\n
My strlcpy()<\/em> function uses int<\/em> variable offset<\/code> to track copying from src<\/code> to dst<\/code>. An if<\/em> test immediately determines whether the dstsize<\/code> value is valid:<\/p>\n
if( dstsize > 0 )<\/code><\/p>\n
If not, the dst<\/code> string is capped (a must) at Line 27:<\/p>\n
*(dst+offset) = '\\0';<\/code><\/p>\n
When the dstsize<\/code> value is legitimate (greater than zero) a while<\/em> loop at Line 12 copies the characters from src<\/code> to dst<\/code>. Line 15 ensures that only dstsize<\/code> characters (or fewer) are copied. Copying takes place at Line 22. And the offset<\/code> variable is incremented at Line 23.<\/p>\n
The final while<\/em> loop at Line 30 counts the length of the scr<\/code> string. I couldn’t use the strlen()<\/em> function because doing so requires including the string.h<\/code> header file. This inclusion results in a slew of warnings and errors because of my strlcpy()<\/em> function and its conflicting definition with strlcpy()<\/em> supplied by the system’s C library.<\/p>\n
My code’s output matched that of the control program, so I think I’m good. Had I not cross-checked my version with the one supplied with the compiler, it would have returned different values. In fact, the man<\/em> page for strlcpy()<\/em> contains extensive notes and examples to explain how the return value is used. It’s interesting information, especially if you are to properly concoct your own, similar — and compatible — function.<\/p>\n
Next week I tackle the strlcat()<\/em> function.<\/p>\n","protected":false},"excerpt":{"rendered":"
Crafting my own strlcpy<\/em> function was easier after I studied the original function and ran tests on its operation. Continue reading →<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[2],"tags":[],"class_list":["post-3886","post","type-post","status-publish","format-standard","hentry","category-main"],"_links":{"self":[{"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=\/wp\/v2\/posts\/3886","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=3886"}],"version-history":[{"count":7,"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=\/wp\/v2\/posts\/3886\/revisions"}],"predecessor-version":[{"id":3900,"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=\/wp\/v2\/posts\/3886\/revisions\/3900"}],"wp:attachment":[{"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=3886"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=3886"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=3886"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}