{"id":31394,"date":"2023-01-21T04:15:20","date_gmt":"2023-01-20T22:45:20","guid":{"rendered":"https:\/\/jassweb.com\/solved\/solved-reading-a-character-and-a-string-from-a-file-in-c-closed\/"},"modified":"2023-01-21T04:15:20","modified_gmt":"2023-01-20T22:45:20","slug":"solved-reading-a-character-and-a-string-from-a-file-in-c-closed","status":"publish","type":"post","link":"https:\/\/jassweb.com\/solved\/solved-reading-a-character-and-a-string-from-a-file-in-c-closed\/","title":{"rendered":"[Solved] Reading a character and a string from a file in C [closed]"},"content":{"rendered":"<p> [ad_1]<br \/>\n<\/p>\n<div id=\"answer-55108681\" class=\"answer js-answer accepted-answer js-accepted-answer\" data-answerid=\"55108681\" data-parentid=\"55107830\" 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>(I did that answer while <code>R 0x...<\/code> and <code>W 0x...<\/code> was given on the same line rather than two)<\/p>\n<p>If you are <em>sure<\/em> each line of the file contains <code>R&lt;space&gt;0x...&lt;space&gt;W&lt;space&gt;0x...<\/code> then you can do<\/p>\n<pre><code>int main()\n{\n  FILE * fp = fopen(\"in\", \"r\");\n\n  if (fp == NULL) {\n    puts(\"cannot open 'in'\");\n    return -1;\n  }\n\n  char line[100];\n\n  while (fgets(line, sizeof(line), fp)) {\n    char c1, c2;\n    unsigned n1, n2;\n\n    errno = 0;\n    if ((sscanf(line, \"%c %x %c %x\", &amp;c1, &amp;n1, &amp;c2, &amp;n2) == 4) &amp;&amp; !errno) {\n      \/\/ just to indicate it read well\n      printf(\"%c:%x:%c:%x\\n\", c1, n1, c2, n2);\n    }\n    else {\n      printf(\"invalid line %s\\n\", line);\n    }\n  }\n\n  puts(\"done\");\n  fclose(fp);\n}\n<\/code><\/pre>\n<p>Compilation and execution<\/p>\n<pre><code>pi@raspberrypi:\/tmp $ gcc -pedantic -Wextra f.c\npi@raspberrypi:\/tmp $ cat in\nR 0x1 W 0x2\nA 0x123 Z 0x345\nC 0x0 Z 0x678\npi@raspberrypi:\/tmp $ .\/a.out\nR:1:W:2\nA:123:Z:345\nC:0:Z:678\ndone\n<\/code><\/pre>\n<p>Note I first read the line to not be disturbed by the newline etc<\/p>\n<hr>\n<p>If you can have several spaces and\/or may be tabs between the field and\/or even at the beginning of the line you can use <em>strtok<\/em> :<\/p>\n<pre><code>#include &lt;stdio.h&gt;\n#include &lt;string.h&gt;\n#include &lt;errno.h&gt;\n\nint getChar(char * c, char * s, int n)\n{\n  if (s == NULL) {\n    printf(\"field %d is missing\\n\", n);\n    return 0;\n  }\n  if (s[1] != 0) {\n    printf(\"invalid field %d : '%s'\\n\", n, s);\n    return 0;\n  }\n\n  *c = s[0];\n  return 1;\n}\n\nint getUnsigned(unsigned * u, char * s, int n)\n{\n  if (s == NULL) {\n    printf(\"field %d is missing\\n\", n);\n    return 0;\n  }\n\n  char c;\n\n  errno = 0;\n  if ((sscanf(s, \"%x%c\", u, &amp;c) != 1) || (errno != 0)) {\n    printf(\"invalid field %d : '%s'\\n\", n, s);\n    return 0;\n  }\n\n  return 1;\n}\n\nint main()\n{\n  FILE * fp = fopen(\"in\", \"r\");\n\n  if (fp == NULL) {\n    puts(\"cannot open 'in'\");\n    return -1;\n  }\n\n  char line[100];\n\n  while (fgets(line, sizeof(line), fp)) {\n    char c1, c2;\n    unsigned n1, n2;\n\n    if (getChar(&amp;c1, strtok(line, \" \\t\"), 0) &amp;&amp;\n        getUnsigned(&amp;n1, strtok(NULL, \" \\t\"), 1) &amp;&amp;\n        getChar(&amp;c2, strtok(NULL, \" \\t\"), 2) &amp;&amp;\n        getUnsigned(&amp;n2, strtok(NULL, \" \\t\\n\"), 3)) \/* warning \\n is added *\/\n      \/\/ just to indicate it read well\n      printf(\"%c:%x:%c:%x\\n\", c1, n1, c2, n2);\n  }\n\n  puts(\"done\");\n  fclose(fp);\n}\n<\/code><\/pre>\n<p>Compilation and execution :<\/p>\n<pre><code>pi@raspberrypi:\/tmp $ gcc -pedantic -Wextra ff.c\npi@raspberrypi:\/tmp $ cat in\n R 0x1   W  0x2\nA    0x123 Z 0x345\n    C 0x0  Z     0x678\npi@raspberrypi:\/tmp $ .\/a.out\nR:1:W:2\nA:123:Z:345\nC:0:Z:678\ndone\n<\/code><\/pre>\n<\/p><\/div>\n<div class=\"mt24\"><\/div>\n<\/div>\n<p>            <span class=\"d-none\" itemprop=\"commentCount\">2<\/span> <\/p><\/div>\n<\/div>\n<p>[ad_2]<\/p>\n<p>solved Reading a character and a string from a file in C [closed] <\/p>\n","protected":false},"excerpt":{"rendered":"<p>[ad_1] (I did that answer while R 0x&#8230; and W 0x&#8230; was given on the same line rather than two) If you are sure each line of the file contains R&lt;space&gt;0x&#8230;&lt;space&gt;W&lt;space&gt;0x&#8230; then you can do int main() { FILE * fp = fopen(&#8220;in&#8221;, &#8220;r&#8221;); if (fp == NULL) { puts(&#8220;cannot open &#8216;in'&#8221;); return -1; } &#8230; <a title=\"[Solved] Reading a character and a string from a file in C [closed]\" class=\"read-more\" href=\"https:\/\/jassweb.com\/solved\/solved-reading-a-character-and-a-string-from-a-file-in-c-closed\/\" aria-label=\"More on [Solved] Reading a character and a string from a file in C [closed]\">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":[967,324,5836],"class_list":["post-31394","post","type-post","status-publish","format-standard","hentry","category-solved","tag-c-strings","tag-c","tag-file-processing"],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v26.5 - https:\/\/yoast.com\/wordpress\/plugins\/seo\/ -->\n<title>[Solved] Reading a character and a string from a file in C [closed] - 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-reading-a-character-and-a-string-from-a-file-in-c-closed\/\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"[Solved] Reading a character and a string from a file in C [closed] - JassWeb\" \/>\n<meta property=\"og:description\" content=\"[ad_1] (I did that answer while R 0x... and W 0x... was given on the same line rather than two) If you are sure each line of the file contains R&lt;space&gt;0x...&lt;space&gt;W&lt;space&gt;0x... then you can do int main() { FILE * fp = fopen(&quot;in&quot;, &quot;r&quot;); if (fp == NULL) { puts(&quot;cannot open &#039;in&#039;&quot;); return -1; } ... 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