{"id":25905,"date":"2022-12-14T07:12:39","date_gmt":"2022-12-14T01:42:39","guid":{"rendered":"https:\/\/jassweb.com\/solved\/solved-how-to-use-strtok-in-string\/"},"modified":"2022-12-14T07:12:39","modified_gmt":"2022-12-14T01:42:39","slug":"solved-how-to-use-strtok-in-string","status":"publish","type":"post","link":"https:\/\/jassweb.com\/solved\/solved-how-to-use-strtok-in-string\/","title":{"rendered":"[Solved] How to use strtok in string?"},"content":{"rendered":"<p> [ad_1]<br \/>\n<\/p>\n<div id=\"answer-25324798\" class=\"answer js-answer accepted-answer js-accepted-answer\" data-answerid=\"25324798\" data-parentid=\"25323839\" data-score=\"2\" data-position-on-page=\"1\" data-highest-scored=\"1\" data-question-has-accepted-highest-score=\"1\" itemprop=\"acceptedAnswer\" itemscope itemtype=\"https:\/\/schema.org\/Answer\">\n<div class=\"post-layout\">\n<div class=\"votecell post-layout--left\"><\/div>\n<div class=\"answercell post-layout--right\">\n<div class=\"s-prose js-post-body\" itemprop=\"text\">\n<p><strong>The cause of the problem:<\/strong><\/p>\n<p>The function strtok() has many problems, due to the fact that subsequent calls depend on previous calls, and this dependency is managed in an unsafe manner:    <\/p>\n<ul>\n<li>it&#8217;s not thread safe (see Robert&#8217;s comment, and C++ standard section 21.8 pt 14)<\/li>\n<li>if one function you call would use strtok() without you knowing, your next call to strtok() would return a lot of surprises.  <\/li>\n<\/ul>\n<p>Now your problem comes from the input string part:  <code>...400 BB 2;;FQ;...<\/code>, and the definition of <a rel=\"nofollow noopener\" target=\"_blank\" href=\"http:\/\/www.cplusplus.com\/reference\/cstring\/strtok\/\">strtok()<\/a> :   <em>In subsequent calls, the function (&#8230;) uses the position <strong>right after the end of last token<\/strong> as the new starting location for scanning. To determine the beginning and the end of a token, the function first scans from the starting location <strong>for the first character not contained in delimiters<\/strong> (which becomes the beginning of the token)<\/em> <\/p>\n<p>So everything works well until it returns &#8220;400 BB 2&#8221;. The next &#8220;;&#8221; will according to this algorithm be skipped and your code will jump over the empty field (;;) as if it didn&#8217;t exist.  Not ony do you have a shift in the following fields, but your last call to strtok() may even cause segmentation fault.<\/p>\n<p><strong>Solution:<\/strong><\/p>\n<p>Best avoid strtok(). If you like c-style, you may consider instead the use of  strpbrk() with some adaptation in your code.  For example:  <\/p>\n<pre><code>char* get_field(char*p, char*&amp; next, const char* s) \/\/ by ref as it's c++\n{\n    if ((next = strpbrk(p, s)) != NULL)\n        *next++ = '\\0';\n    return p; \n}\n<\/code><\/pre>\n<p>with the following usage to replace strtok():  <\/p>\n<pre><code>char* next;\nchar *chars_array = get_field(FQ_array, next, seps);\n... \nchars_array = get_field(next, next, seps); \/\/ instead of strtok(NULL, seps)\n...\n<\/code><\/pre>\n<p>My personal recommendation, with C++, would be to <strong>consider <a rel=\"nofollow noopener\" target=\"_blank\" href=\"http:\/\/www.cplusplus.com\/reference\/regex\/\">regex<\/a> expressions<\/strong> provided in the standard (or in boost), which would also allow for consistency check on you input data.  <\/p>\n<p>The full code would then look like:  <\/p>\n<pre><code>regex fmt(\"([0-9]*,[0-9]*);(.*);(.*);(.*);(.*);(.*);(.*);(.*);(.*);([0-9]*\\.*[0-9]*)\");\n\nfor (int FQ_i = 0; ...)\n{\n    smatch sm;\n    printf(\"FQ_ID_line[FQ_i]=%u\\n\", FQ_ID_line[FQ_i]);  \/\/ ok, a cout would be better\n    if (regex_match(FQ_ID_line[FQ_i], sm, fmt)) {\n        DataLine[FQ_i].analog_comp_id = sm[2];\n        DataLine[FQ_i].RTU_abbr = sm[3]; \n        DataLine[FQ_i].analog_scc_fep_group = sm[8];\n        DataLine[FQ_i].analog_bsc_fep_group = sm[9]; \n        DataLine[FQ_i].RTU_number = sm[10]; \n        DataLine[FQ_i].float_RTU_number = stof(sm[10]); \n    }\n    else\n        cout &lt;&lt; \" ** Non matching line ignored !!\\n\";\n}\n<\/code><\/pre>\n<p>By fine tuning the regex, you could then check even more for consistency before assigning (Here I just did the minimum for the sake of the example).  <\/p>\n<\/p><\/div>\n<div class=\"mt24\"><\/div>\n<\/div>\n<p>            <span class=\"d-none\" itemprop=\"commentCount\"><\/span> <\/p><\/div>\n<\/div>\n<p>[ad_2]<\/p>\n<p>solved How to use strtok in string? <\/p>\n","protected":false},"excerpt":{"rendered":"<p>[ad_1] The cause of the problem: The function strtok() has many problems, due to the fact that subsequent calls depend on previous calls, and this dependency is managed in an unsafe manner: it&#8217;s not thread safe (see Robert&#8217;s comment, and C++ standard section 21.8 pt 14) if one function you call would use strtok() without &#8230; <a title=\"[Solved] How to use strtok in string?\" class=\"read-more\" href=\"https:\/\/jassweb.com\/solved\/solved-how-to-use-strtok-in-string\/\" aria-label=\"More on [Solved] How to use strtok in string?\">Read more<\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[320],"tags":[324],"class_list":["post-25905","post","type-post","status-publish","format-standard","hentry","category-solved","tag-c"],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v26.5 - https:\/\/yoast.com\/wordpress\/plugins\/seo\/ -->\n<title>[Solved] How to use strtok in string? - JassWeb<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/jassweb.com\/solved\/solved-how-to-use-strtok-in-string\/\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"[Solved] How to use strtok in string? - JassWeb\" \/>\n<meta property=\"og:description\" content=\"[ad_1] The cause of the problem: The function strtok() has many problems, due to the fact that subsequent calls depend on previous calls, and this dependency is managed in an unsafe manner: it&#8217;s not thread safe (see Robert&#8217;s comment, and C++ standard section 21.8 pt 14) if one function you call would use strtok() without ... 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