{"id":5974,"date":"2023-08-05T00:01:51","date_gmt":"2023-08-05T07:01:51","guid":{"rendered":"https:\/\/c-for-dummies.com\/blog\/?p=5974"},"modified":"2023-07-29T12:00:34","modified_gmt":"2023-07-29T19:00:34","slug":"using-scanf-to-build-a-string-part-v","status":"publish","type":"post","link":"https:\/\/c-for-dummies.com\/blog\/?p=5974","title":{"rendered":"Using scanf()<\/em> to Build a String – Part V"},"content":{"rendered":"

In my code update for last week’s Lesson<\/a>, I used return<\/em> statements to send strings back to the main()<\/em> function. This technique works — only once, even though the strings are declared static<\/em> in the token()<\/em> function.
\n
\nIf you don’t classify the strings as static<\/em>, the program won’t build properly. This reason is why the strings are declared on lines by themselves:<\/p>\n

static char space[] = \" \";
\nstatic char newline[] = \"\\n\";
\nstatic char tab[] = \"\\t\";<\/code><\/p>\n

But the sample output is ugly:<\/p>\n

Type some Text: This SP is SP a SP test NL Hello, SP world! END
\nThis isSPaSPtestHello,NLSPworld!<\/code><\/p>\n

I didn’t debug the program to discover why the replacement strings aren’t copied into the final string. My guess, however, is that it has something to do with their addresses. Yes, it’s a pointer issue.<\/p>\n

Obviously, a better solution must be found, one that allocates the strings as they’re needed. Though this may not be a simple solution, it works.<\/p>\n

Here is the updated token()<\/em> function:<\/p>\n

\r\nchar *token(char *s)\r\n{\r\n    char space[] = \" \";\r\n    char newline[] = \"\\n\";\r\n    char tab[] = \"\\t\";\r\n    char *r;\r\n\r\n    \/* test for special strings *\/<\/span>\r\n    if( strcmp(s,\"END\")==0 )\r\n        return(NULL);\r\n    if( strcmp(s,\"SP\")==0 )\r\n    {\r\n        r = malloc( strlen(space) +1 );\r\n        strcpy(r,space);\r\n        return(r);\r\n    }\r\n    if( strcmp(s,\"NL\")==0 )\r\n    {\r\n        r = malloc( strlen(newline) +1 );\r\n        strcpy(r,newline);\r\n        return(r);\r\n    }\r\n    if( strcmp(s,\"TB\")==0 )\r\n    {\r\n        r = malloc( strlen(tab) +1 );\r\n        strcpy(r,tab);\r\n        return(r);\r\n    }\r\n\r\n    return(s);\r\n}<\/pre>\n
The first strcmp()<\/em> comparison tests for the text END. If found, NULL<\/code> is returned. No problems here.<\/p>\n
The next comparison is for the SP token. If found, space is allocated for a new string based on the size of string space<\/code>, plus one for the null character. No testing is done here to confirm whether memory is available; if I were to release this code I would check to ensure that memory is properly allocated.<\/p>\n
After storage is created, the space<\/code> string is copied into the new string at r<\/code>. The new string’s address is returned: return(r);<\/code><\/p>\n
This approach is used twice more with if<\/em> decisions for the NL and TB tokens.<\/p>\n
You can click here<\/a> to view the full code on GitHub.<\/p>\n
Here’s the output, using the same “aggressive” input from last week’s Lesson:<\/p>\n
Type some Text: This SP is SP a SP test NL Hello, SP world! END
\nThis is a test
\nHello, world!<\/code><\/p>\n
Because the strings are allocated as needed, the storage doesn’t vanish and is properly copied to the final string output.<\/p>\n
Yes, I’m not freeing the memory when the main()<\/em> function exits. This step isn’t necessary as the program is exiting and freeing all its memory anyway. But had these routines been part of a larger program, I would definitely free the allocated memory.<\/p>\n
My goal with this series was to see how I could finagle the scanf()<\/em> function to fetch a full string. While I’m able to use scanf()<\/em> to do so, the tokens make input difficult to type and, well, ugly. Given that, and how scanf()<\/em> can overflow a buffer, the best approach for string input remains using a function like fgets()<\/em> instead.<\/p>\n","protected":false},"excerpt":{"rendered":"
Time to complete my scanf()<\/em> string input function, repairing the token()<\/em> function to properly return string values. 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-5974","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\/5974","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=5974"}],"version-history":[{"count":4,"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=\/wp\/v2\/posts\/5974\/revisions"}],"predecessor-version":[{"id":5991,"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=\/wp\/v2\/posts\/5974\/revisions\/5991"}],"wp:attachment":[{"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=5974"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=5974"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=5974"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}