{"id":5053,"date":"2022-08-26T06:43:37","date_gmt":"2022-08-26T01:13:37","guid":{"rendered":"https:\/\/jassweb.com\/solved\/solved-null-terminated-c-character-arrays\/"},"modified":"2022-08-26T06:43:37","modified_gmt":"2022-08-26T01:13:37","slug":"solved-null-terminated-c-character-arrays","status":"publish","type":"post","link":"https:\/\/jassweb.com\/solved\/solved-null-terminated-c-character-arrays\/","title":{"rendered":"[Solved] Null terminated C character arrays"},"content":{"rendered":"<p> [ad_1]<br \/>\n<\/p>\n<div id=\"answer-56680223\" class=\"answer js-answer accepted-answer js-accepted-answer\" data-answerid=\"56680223\" data-parentid=\"56679169\" 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>First, <code>\"sample\"<\/code> is called a string literal. It declares a const char array terminated with a null character.<\/p>\n<p>Let us go on:<\/p>\n<pre><code>    char arr[]=\"sample\";\n<\/code><\/pre>\n<p>The right hand part in a const char array of size 7 (6 characters and a <code>'\\0'<\/code>. The dimension of arr is deduced from its initialization and is also 7. The char array is then initialized from the literal string.<\/p>\n<pre><code>    char arr2[6]=\"sample\";\n<\/code><\/pre>\n<p><code>arr2<\/code> has a declared size of 6. It is initialized from a string literal of size 7: only the 6 declared position are initialized to <code>{'s', 'a', 'm', 'p', 'l', 'e'}<\/code> <strong>with no terminating null<\/strong>. Nothing is wrong here, except that passing <code>arr2<\/code> to a function that expects a null terminated string invokes Undefined Behaviour.<\/p>\n<pre><code>    char arr3[7]=\"sample\";\n<\/code><\/pre>\n<p>Declared size an initialization literal string size are both 7: it is just an explicit version of the first use case. Rather dangerous because if you later add one character to the initialization string you will get a not null terminated char array.<\/p>\n<pre><code>    char* strarr=\"sample\";  \n<\/code><\/pre>\n<p><strong>Avoid that<\/strong>. You are declaring a non const char pointer on a string literal. While the standard declares explicitely:<\/p>\n<blockquote>\n<p>If the program attempts to modify such an array, the behavior is<br \/>\n  undefined.<\/p>\n<\/blockquote>\n<p><code>strarr[3] = 'i'<\/code> would then invoke Undefined Behaviour with no warning. That being said and provided you never modify the string, you have a nice null terminated string.<\/p>\n<pre><code>    char* strarr1=arr;\n<\/code><\/pre>\n<p>Ok, you declare a pointer to another string. Or more exactly a pointer to the first character of another string. And it is correctly null terminated.<\/p>\n<pre><code>    char* strarr2=arr2; \n<\/code><\/pre>\n<p>You have a pointer to the first character of a not null terminated char array&#8230; You could not pass <code>arr2<\/code> to a function expecting a null terminated char array, and you cannot either pass <code>strarr2<\/code>.<\/p>\n<pre><code>    char* strarr3=arr3;\n<\/code><\/pre>\n<p>You have another pointer pointing to a string. Same behaviour as <code>strarr1<\/code>.<\/p>\n<hr>\n<p>As per <em>how to check in gdb for the terminating null<\/em>, you cannot print it directly, because gdb knows enough of C strings to automatically stop printing a string on first null character. But you can always use  <code>p arr[7]<\/code> to see whether the character after the array is a null or not.<\/p>\n<p>For <code>arr2<\/code>, <code>arr2+7<\/code> is one past the array. So it is undefined what lies there and in a truely bad system, using <code>p arr[7]<\/code> could raise a signal because it could be after the end of a memory segment &#8211; but I must admit that I have never seen that&#8230;<\/p>\n<\/p><\/div>\n<div class=\"mt24\"><\/div>\n<\/div>\n<p>            <span class=\"d-none\" itemprop=\"commentCount\">9<\/span> <\/p><\/div>\n<\/div>\n<p>[ad_2]<\/p>\n<p>solved Null terminated C character arrays <\/p>\n","protected":false},"excerpt":{"rendered":"<p>[ad_1] First, &#8220;sample&#8221; is called a string literal. It declares a const char array terminated with a null character. Let us go on: char arr[]=&#8221;sample&#8221;; The right hand part in a const char array of size 7 (6 characters and a &#8216;\\0&#8217;. The dimension of arr is deduced from its initialization and is also 7. &#8230; <a title=\"[Solved] Null terminated C character arrays\" class=\"read-more\" href=\"https:\/\/jassweb.com\/solved\/solved-null-terminated-c-character-arrays\/\" aria-label=\"More on [Solved] Null terminated C character arrays\">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":[361,967,324,712],"class_list":["post-5053","post","type-post","status-publish","format-standard","hentry","category-solved","tag-arrays","tag-c-strings","tag-c","tag-pointers"],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v26.5 - https:\/\/yoast.com\/wordpress\/plugins\/seo\/ -->\n<title>[Solved] Null terminated C character arrays - 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-null-terminated-c-character-arrays\/\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"[Solved] Null terminated C character arrays - JassWeb\" \/>\n<meta property=\"og:description\" content=\"[ad_1] First, &quot;sample&quot; is called a string literal. 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