{"id":5213,"date":"2022-02-26T00:01:57","date_gmt":"2022-02-26T08:01:57","guid":{"rendered":"https:\/\/c-for-dummies.com\/blog\/?p=5213"},"modified":"2022-02-19T10:53:50","modified_gmt":"2022-02-19T18:53:50","slug":"how-many-characters-output","status":"publish","type":"post","link":"https:\/\/c-for-dummies.com\/blog\/?p=5213","title":{"rendered":"How Many Characters Output?"},"content":{"rendered":"

I don’t think I’ve ever used the return value from a printf()<\/em> statement. Yes, the function has an int<\/em> return value, which is the number of characters output. This value can be difficult to guess.
\n
\nHere’s your sample code, which I use throughout this Lesson:<\/p>\n

2022_02_26-Lesson.c<\/a><\/h3>\n
\r\n#include <stdio.h>\r\n\r\nint main()\r\n{\r\n    int r;\r\n\r\n    r = printf(\"Goodbye, cruel world!\\n\");\r\n\r\n    printf(\"%d characters output\\n\",r);\r\n\r\n    return(0);\r\n}<\/pre>\n
The program outputs a string, then the number of characters output:<\/p>\n
Goodbye, cruel world!
\n22 characters output<\/code><\/p>\n
The string \"Goodbye, cruel world!\\n\"<\/code> contains 23 characters when you count the \\n<\/code> escape sequence as two characters. But the compiler sees it as a single character (the newline), which is what’s output. The printf()<\/em> function accurately returns the number of characters output.<\/p>\n
Now change Line 7 in the code to read:<\/p>\n
r = printf(\"%d * %d = %d\\n\",400,500,400*500);<\/code><\/p>\n
The format string contains 14 characters, of which 13 are single characters (remember that \\n<\/code> is one character). The output, however, is longer:<\/p>\n
400 * 500 = 200000
\n19 characters output<\/code><\/p>\n
A diversion C programming nerds like to play on each other is to guess the printf()<\/em> statement’s return value. The format string can get quite complex, which thrills the nerds to no end:<\/p>\n
r = printf(\"%*s\\n\",34,\"Wow!\");<\/code><\/p>\n
The above printf()<\/em> statement uses the *<\/code> variable width item<\/a> in the %s<\/code> placeholder. The output is based on the second argument 34. So the string \"Wow!\"<\/code> is output within a chunk of spaces 34 characters wide, right-justified. Then comes the newline.<\/p>\n
Can you guess the value of variable r<\/code> after the above statement executes?<\/p>\n
[tick-tock…]<\/em><\/p>\n
My first guess — impulsive and irrational — was 38. Wrong. I figured 34 spaces plus \"Wow!\"<\/code> and I missed the newline. But this incorrect and hasty assumption forgot how the *<\/code> wildcard works. Regardless, run the code to view the correct answer:<\/p>\n
                              Wow!
\n35 characters output<\/code><\/p>\n
If the *<\/code> width is 34, the string output is always 34 characters long, plus one for the newline. The return value confirms the number of characters output.<\/p>\n
As I wrote earlier, I don’t recall ever using the printf()<\/em> return value in my code. I’ve never had a practical reason for its application. After all, it seems a bit tardy: If you’re concerned about outputting characters of a given width, the value returned from printf()<\/em> is available only after the text is output.<\/p>\n
The man<\/em> page explains that most printf()<\/em> family functions return the number of characters output, minus the trailing null character, \\0<\/code>. The snprintf()<\/em> and vsnprintf()<\/em> functions are different: They return the number of characters that would be output if the output size weren’t restricted.<\/p>\n
While its return value offers the exact number of characters output, another feature of the printf()<\/em> function allows you to monitor the number of characters output at a given position within the format string. This oddball is the %n<\/code> conversion character — the use of which is fraught with danger and intrigue. I write more about this placeholder in next week’s Lesson.<\/p>\n","protected":false},"excerpt":{"rendered":"
Though it’s seldom used, the printf()<\/em> function has a return value. 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-5213","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\/5213","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=5213"}],"version-history":[{"count":5,"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=\/wp\/v2\/posts\/5213\/revisions"}],"predecessor-version":[{"id":5225,"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=\/wp\/v2\/posts\/5213\/revisions\/5225"}],"wp:attachment":[{"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=5213"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=5213"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=5213"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}