{"id":7644,"date":"2026-06-27T00:01:03","date_gmt":"2026-06-27T07:01:03","guid":{"rendered":"https:\/\/c-for-dummies.com\/blog\/?p=7644"},"modified":"2026-06-20T11:37:49","modified_gmt":"2026-06-20T18:37:49","slug":"ctype-function-isxdigit","status":"publish","type":"post","link":"https:\/\/c-for-dummies.com\/blog\/?p=7644","title":{"rendered":"Ctype Function: isxdigit()<\/em>"},"content":{"rendered":"

\"\"
\nThe ctype isxdigit()<\/em> function returns TRUE for any digit you find in a hexadecimal number. I suppose this function has a role to play, most likely in detecting hexadecimal characters in a string. Regardless, this post wraps up my exploration of the ctype functions<\/a>.
\n
\nHexadecimal values include numbers zero through 9 plus the letters A through F, both upper- and lowercase, to represent values 0 through 15. This counting base (16 or hexadecimal) is common in computerdom as it provides a quick way to reference bits, which are typically arranged in groups of four:<\/p>\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n
Bits<\/td>\nHex<\/td>\nDecimal<\/td>\n<\/tr>\n
0000<\/td>\n0<\/td>\n0<\/td>\n<\/tr>\n
0001<\/td>\n1<\/td>\n1<\/td>\n<\/tr>\n
0010<\/td>\n2<\/td>\n2<\/td>\n<\/tr>\n
0011<\/td>\n3<\/td>\n3<\/td>\n<\/tr>\n
0100<\/td>\n4<\/td>\n4<\/td>\n<\/tr>\n
0101<\/td>\n5<\/td>\n5<\/td>\n<\/tr>\n
0110<\/td>\n6<\/td>\n6<\/td>\n<\/tr>\n
0111<\/td>\n7<\/td>\n7<\/td>\n<\/tr>\n
1000<\/td>\n8<\/td>\n8<\/td>\n<\/tr>\n
1001<\/td>\n9<\/td>\n9<\/td>\n<\/tr>\n
1010<\/td>\nA<\/td>\n10<\/td>\n<\/tr>\n
1011<\/td>\nB<\/td>\n11<\/td>\n<\/tr>\n
1100<\/td>\nC<\/td>\n12<\/td>\n<\/tr>\n
1101<\/td>\nD<\/td>\n13<\/td>\n<\/tr>\n
1110<\/td>\nE<\/td>\n14<\/td>\n<\/tr>\n
1111<\/td>\nF<\/td>\n15<\/td>\n<\/tr>\n<\/table>\n

Truly, you can’t consider yourself a nerd until you know how to count in hex, or can quickly translate hex values such as 0x20 and 0x41 into their decimal equivalents and vice-versa.<\/p>\n

I went to a restaurant where the waiter wore a shirt with a series of hex values. I don’t need to tell you that I was only customer ever to read the text those codes represented. (I forget what it said, specifically.) #nerd<\/p><\/blockquote>\n

The isxdigit()<\/em> function returns TRUE if the character examined is a number, 0 through 9, uppercase letter, A through Z, or lowercase letter, a through z.<\/p>\n

Here is sample code that plows through the printable ASCII code values and plucks out hex digits:<\/p>\n

2026_06_27-Lesson-a.c<\/a><\/h3>\n
\r\n#include <stdio.h>\r\n#include <ctype.h>\r\n\r\nint main()\r\n{\r\n    int ch;\r\n\r\n    puts(\"X Digits:\");\r\n    \/* ASCII character range *\/<\/span>\r\n    for( ch=' '; ch<='~'; ch++ )\r\n        if( isxdigit(ch) )\r\n            putchar(ch);\r\n    putchar('\\n');\r\n\r\n    return 0;\r\n}<\/pre>\n
The for<\/em> loop runs the gamut of ASCII codes from space through tilde. I could have used the isprint()<\/em> function<\/a> here, but didn’t want to stack up too many custom ctype functions in my version of the code (below).<\/p>\n
In the if<\/em> test, the isxdigit()<\/em> function returns TRUE for a hexadecimal digit, which is output as shown in this sample run:<\/p>\n
X Digits:\r\n0123456789ABCDEFabcdef<\/pre>\n
To emulate the isxdigit()<\/em> function, I use a series of if<\/em> tests to weed out the three ranges of ASCII characters found in a hexadecimal value: 0 to 9, A to Z, and a to z:<\/p>\n
2026_06_27-Lesson-b.c<\/a><\/h3>\n
\r\n#include <stdio.h>\r\n#include <stdbool.h>\r\n\r\nint isxdigit(int c)\r\n{\r\n    if( c>='0' && c<='9' )\r\n        return true;\r\n    if( c>='A' && c<='F' )\r\n        return true;\r\n    if( c>='a' && c<='f' )\r\n        return true;\r\n\r\n    return false;\r\n}\r\n\r\nint main()\r\n{\r\n    int ch;\r\n\r\n    puts(\"X Digits:\");\r\n    \/* ASCII character range *\/<\/span>\r\n    for( ch=' '; ch<='~'; ch++ )\r\n        if( isxdigit(ch) )\r\n            putchar(ch);\r\n    putchar('\\n');\r\n\r\n    return 0;\r\n}<\/pre>\n
The program’s output is the same.<\/p>\n
To conclude this series, I would comment that the ctype functions don’t really carry a lot of weight in the Unicode era. It would be nice to see extended ctype functions available that truly understand different locales. Then again, with a knowledge of a programming language like C, you can always code your own functions. Heck, draw up a library! Anything is possible.<\/p>\n","protected":false},"excerpt":{"rendered":"
No, the isxdigit<\/em> function doesn’t identify former digit characters. The “x” here refers to hexadecimal. 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-7644","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\/7644","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=7644"}],"version-history":[{"count":7,"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=\/wp\/v2\/posts\/7644\/revisions"}],"predecessor-version":[{"id":7659,"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=\/wp\/v2\/posts\/7644\/revisions\/7659"}],"wp:attachment":[{"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=7644"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=7644"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=7644"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}