{"id":34570,"date":"2023-03-31T01:05:42","date_gmt":"2023-03-30T19:35:42","guid":{"rendered":"https:\/\/jassweb.com\/solved\/solved-realloc-fails-when-printf-is-in-code-weird-chars\/"},"modified":"2023-03-31T01:05:42","modified_gmt":"2023-03-30T19:35:42","slug":"solved-realloc-fails-when-printf-is-in-code-weird-chars","status":"publish","type":"post","link":"https:\/\/jassweb.com\/solved\/solved-realloc-fails-when-printf-is-in-code-weird-chars\/","title":{"rendered":"[Solved] realloc fails when printf is in code \/ weird chars"},"content":{"rendered":"<p> [ad_1]<br \/>\n<\/p>\n<div id=\"answer-75174655\" class=\"answer js-answer accepted-answer js-accepted-answer\" data-answerid=\"75174655\" data-parentid=\"75174400\" data-score=\"1\" 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>Your code exhibits undefined behaviour because you passed a non-static, uninitialised pointer to <code>realloc<\/code> whose contents were indeterminate.<\/p>\n<p><em>From C11, Memory Management Functions:<\/em><\/p>\n<blockquote>\n<p>The realloc function deallocates the old object pointed to by ptr and<br \/>\nreturns a pointer to a new object that has the size specified by size.<br \/>\n<strong>&#8230;.if ptr does not match a pointer earlier returned by a memory<br \/>\nmanagement function, or if the space has been deallocated by a call to<br \/>\nthe free or realloc function, the behavior is undefined.<\/strong><\/p>\n<\/blockquote>\n<hr>\n<p>Possible fixes:<\/p>\n<ul>\n<li>Initialize it with <code>0<\/code> \/ <code>NULL<\/code>.<\/li>\n<li>Declare it as <code>static<\/code>.\u00b9<\/li>\n<li>Replace it with a call to <code>malloc<\/code>.<\/li>\n<\/ul>\n<hr>\n<blockquote>\n<p>The realloc function returns a pointer to the new object (which may<br \/>\nhave the same value as a pointer to the old object), or a null pointer<br \/>\nif the new object could not be allocated.<\/p>\n<\/blockquote>\n<p><code>realloc<\/code> returns <code>NULL<\/code> on failure, your code should check for it.<\/p>\n<pre><code>#include &lt;errno.h&gt;\n\nchar *line = 0;\nerrno = 0;\n\nchar *new = realloc (line, size);\nif (!new) {\n    perror (\"realloc\");\n    \/* realloc() failed to allocate memory, handle error accordingly. *\/\n}\n<\/code><\/pre>\n<p>The above code snippet can be rewritten as:<\/p>\n<pre><code>#include &lt;errno.h&gt;\n\nerrno = 0;\n\nchar *new = malloc (size);\nif (!new) {\n    perror (\"malloc\");\n    \/* malloc() failed to allocate memory, handle error accordingly. *\/\n}\n\n<\/code><\/pre>\n<hr>\n<p>Similarly, <code>opendir<\/code> returns a <code>NULL<\/code> pointer while <code>lstat<\/code> returns -1 to indicate an error. Check for them.<\/p>\n<hr>\n<p>[1] \u2014 Objects declared with static storage duration and are always initialised. In the absence of a definition, they are implicitly initialised to 0.<\/p>\n<p>From the C standard C11 6.7.9\/10:<\/p>\n<blockquote>\n<p>&#8220;&#8230; If an object that has static or thread storage duration is not<br \/>\ninitialized explicitly, then:<\/p>\n<p>\u2014 <strong>if it has pointer type, it is initialized to a null pointer<\/strong>;<\/p>\n<p>\u2014 if it has arithmetic type, it is initialized to (positive or<br \/>\nunsigned) zero;&#8221;<\/p>\n<\/blockquote>\n<p>Though, it&#8217;s good practice to explicitly set it to 0.<\/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 realloc fails when printf is in code \/ weird chars <\/p>\n","protected":false},"excerpt":{"rendered":"<p>[ad_1] Your code exhibits undefined behaviour because you passed a non-static, uninitialised pointer to realloc whose contents were indeterminate. From C11, Memory Management Functions: The realloc function deallocates the old object pointed to by ptr and returns a pointer to a new object that has the size specified by size. &#8230;.if ptr does not match &#8230; <a title=\"[Solved] realloc fails when printf is in code \/ weird chars\" class=\"read-more\" href=\"https:\/\/jassweb.com\/solved\/solved-realloc-fails-when-printf-is-in-code-weird-chars\/\" aria-label=\"More on [Solved] realloc fails when printf is in code \/ weird chars\">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":[324,3906,535,2162],"class_list":["post-34570","post","type-post","status-publish","format-standard","hentry","category-solved","tag-c","tag-ls","tag-memory","tag-realloc"],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v26.5 - https:\/\/yoast.com\/wordpress\/plugins\/seo\/ -->\n<title>[Solved] realloc fails when printf is in code \/ weird chars - 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-realloc-fails-when-printf-is-in-code-weird-chars\/\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"[Solved] realloc fails when printf is in code \/ weird chars - JassWeb\" \/>\n<meta property=\"og:description\" content=\"[ad_1] Your code exhibits undefined behaviour because you passed a non-static, uninitialised pointer to realloc whose contents were indeterminate. 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