{"id":646,"date":"2014-04-19T00:01:06","date_gmt":"2014-04-19T07:01:06","guid":{"rendered":"http:\/\/c-for-dummies.com\/blog\/?p=646"},"modified":"2014-11-22T10:10:32","modified_gmt":"2014-11-22T18:10:32","slug":"scanf-the-bastard","status":"publish","type":"post","link":"https:\/\/c-for-dummies.com\/blog\/?p=646","title":{"rendered":"scanf()<\/em> the Bastard"},"content":{"rendered":"

When you first learn the C language, and you’re practicing basic input\/output, you become familiar with the two I\/O workhorses of the C library: printf()<\/em> and scanf()<\/em>. Of the two, printf()<\/em> is my favorite. The scanf()<\/em> function is highly useful, and it’s a great learning tool, but it’s not the best function for reading in a string of text.
\n
\nThe scanf()<\/em> function scans formatted<\/em> input. It uses the same placeholders, or conversion characters, as the printf()<\/em> function. So when your code desires an unsigned int<\/em> value, you use the %u<\/code> and scanf()<\/em> grabs only that value. In fact, it diligently rejects any non unsigned int<\/em> value. (That’s a feature that can throw off some programmers.)<\/p>\n

When used with the %s<\/code> placeholder, scanf()<\/em> reads in strings — but only up until the first white space character. That limits scanf()<\/em>‘s definition of a string, which is frustrating.<\/p>\n

\r\n#include <stdio.h>\r\n\r\nint main()\r\n{\r\n    char name[64];\r\n    char color[24];\r\n\r\n    printf(\"Your first and last name: \");\r\n    scanf(\"%s\",name);\r\n    printf(\"Your favorite color: \");\r\n    scanf(\"%s\",color);\r\n\r\n    printf(\"%s's favorite color is %s.\\n\",\r\n        name,\r\n        color);\r\n\r\n    return(0);\r\n}<\/pre>\n
If you type in and run the above code, you may experience the following indigestion while running the program:<\/p>\n
Your first and last name: Dan Gookin<\/span>
\nYour favorite color: Dan's favorite color is Gookin.<\/code><\/p>\n
Because the text Dan Gookin<\/code> contains a space, the scanf()<\/em> function stops reading after the first word, Dan<\/code>. The rest of the text remains in the input stream, where it’s read by the second scanf()<\/em> function and assigned to the color<\/code> variable. The output is predicatble — but only if you’re familiar with the nature of the scanf()<\/em> function.<\/p>\n
Can you work around this limitation?<\/p>\n
No!<\/p>\n
Don’t even try to fake out scanf()<\/em> and attempt to read in more text or avoid the issue. You can’t modify input nor can you fool the function in other ways.<\/p>\n
Now I’ve read that some compliers may allow the *<\/code> wildcard to be inserted into the %s<\/code> placeholder. That trick doesn’t work on any of my machines, therefore I wouldn’t rely upon it for squat.<\/p>\n
If you really need to read in a full string of text, then use a proper function. For example, the fgets()<\/em> function can read text from the input stream. You can read about this function in my books, as well as my June 1, 2013 Lesson<\/a>.<\/p>\n","protected":false},"excerpt":{"rendered":"
The scanf()<\/em> function is a basic input function, but it’s not the best for grabbing strings of text. Continue reading →<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[2],"tags":[],"class_list":["post-646","post","type-post","status-publish","format-standard","hentry","category-main"],"_links":{"self":[{"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=\/wp\/v2\/posts\/646","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=646"}],"version-history":[{"count":7,"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=\/wp\/v2\/posts\/646\/revisions"}],"predecessor-version":[{"id":1121,"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=\/wp\/v2\/posts\/646\/revisions\/1121"}],"wp:attachment":[{"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=646"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=646"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=646"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}