{"id":23148,"date":"2022-11-24T06:07:27","date_gmt":"2022-11-24T00:37:27","guid":{"rendered":"https:\/\/jassweb.com\/solved\/solved-malloc-void-return-char-array-somtimes-not-working-terry-davis-was-right-about-c\/"},"modified":"2022-11-24T06:07:27","modified_gmt":"2022-11-24T00:37:27","slug":"solved-malloc-void-return-char-array-somtimes-not-working-terry-davis-was-right-about-c","status":"publish","type":"post","link":"https:\/\/jassweb.com\/solved\/solved-malloc-void-return-char-array-somtimes-not-working-terry-davis-was-right-about-c\/","title":{"rendered":"[Solved] malloc void return char array somtimes not working (terry davis was right about C++);"},"content":{"rendered":"<p> [ad_1]<br \/>\n<\/p>\n<div id=\"answer-52410659\" class=\"answer js-answer accepted-answer js-accepted-answer\" data-answerid=\"52410659\" data-parentid=\"52410315\" data-score=\"0\" 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>One of the problem to cause undefined behavior is<\/p>\n<p>In <code>void update_typeArray(char * char_array, int index, char input)<\/code><br \/>\nyou free the memory pointed by the <code>__array_buffer<\/code> using  <code>char_array<\/code>.<\/p>\n<pre><code> update_typeArray(__array_buffer, index, __char_buffer);\n\n free(char_array);\n<\/code><\/pre>\n<p>and you allocate the new memory to <code>char_array<\/code><\/p>\n<pre><code>char_array = (char*)malloc(sizeof(char)*(index + 1));\/\/+1 cause string\n<\/code><\/pre>\n<p>but your <code>__array_buffer<\/code> will be still pointing to freed memory.<\/p>\n<p>and you continue to use the <code>__array_buffer<\/code> in <code>main<\/code> after freeing<\/p>\n<p><code>compare_typeArray(__array_buffer,\"a\",size,blist);<\/code><\/p>\n<p><code>free(__array_buffer)<\/code> <\/p>\n<p><strong>To understand easily consider below pictures.<\/strong><\/p>\n<pre><code> ----------------             -------\n| __array_buffer |  -------&gt; | memory| \n  ---------------             -------\n<\/code><\/pre>\n<p>after call <code>update_typeArray(__array_buffer, index, __char_buffer);<\/code><\/p>\n<pre><code>     ----------------             -------\n    | __array_buffer |  -------&gt; | memory| \n      ---------------             -------\n                                   ^\n                                   |\n                            ----------------\n                           |    char_array |   \n                             ---------------  \n<\/code><\/pre>\n<p>after     <code>free(char_array);<\/code><\/p>\n<pre><code> ----------------             \n| __array_buffer |  -------&gt;   X \n  ---------------             \n                               ^\n                               |\n                        ----------------\n                       |   char_array   |   \n                         ---------------  \n<\/code><\/pre>\n<p>After <code>char_array = (char*)malloc(sizeof(char)*(index + 1));\/\/+1 cause string<br \/>\n<\/code><\/p>\n<pre><code>     ----------------             \n    | __array_buffer |  -------&gt;   X \n      ---------------             \n\n\n  ----------------           -------\n |  char_array    | -----&gt; | memory| \n   ---------------           -------\n<\/code><\/pre>\n<p><strong>Solution:<\/strong><\/p>\n<p>If you want to <code>__array_buffer<\/code> to point to new memory you got use pointer to pointer as below.<\/p>\n<p><code>void update_typeArray(char ** char_array, int index, char input)<\/code><\/p>\n<p>and you call the update_type.<\/p>\n<p><code>update_typeArray(&amp;__array_buffer, index, __char_buffer);<\/code><\/p>\n<p>your update_typeArray may look like below.<\/p>\n<pre><code>void update_typeArray(char **char_array, int index, char input)\n{\n\n\n    char * new_array = (char*)malloc(sizeof(char)*(index + 1));\/\/+1 cause string\n\n\n    for (int i = 0; i &lt;= index; i++)\n    {\n        if (i &lt; index)\n        {\n            new_array[i] = (*char_array)[i];\n        }\n        if (i == index)\n        {\n            new_array[i] = '\\0';\/\/'\\000' cause string\n        }\n    }\n\n    free(*char_array);\n    new_array[index - 1] = input;\n    *char_array = (char*)malloc(sizeof(char)*(index + 1));\/\/+1 cause string\n\n    for (int i = 0; i &lt;= index; i++)\n    {\n        if (i &lt; index)\n        {\n            (*char_array)[i] = new_array[i];\n        }\n        if (i == index)\n        {\n            (*char_array)[i] = '\\0';\/\/'\\000' cause string\n        }\n    }\n\n\n    free(new_array);\n\n}\n<\/code><\/pre>\n<\/p><\/div>\n<div class=\"mt24\"><\/div>\n<\/div>\n<p>            <span class=\"d-none\" itemprop=\"commentCount\">13<\/span> <\/p><\/div>\n<\/div>\n<p>[ad_2]<\/p>\n<p>solved malloc void return char array somtimes not working (terry davis was right about C++); <\/p>\n","protected":false},"excerpt":{"rendered":"<p>[ad_1] One of the problem to cause undefined behavior is In void update_typeArray(char * char_array, int index, char input) you free the memory pointed by the __array_buffer using char_array. update_typeArray(__array_buffer, index, __char_buffer); free(char_array); and you allocate the new memory to char_array char_array = (char*)malloc(sizeof(char)*(index + 1));\/\/+1 cause string but your __array_buffer will be still pointing &#8230; 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