{"id":1216,"date":"2015-02-21T00:01:19","date_gmt":"2015-02-21T08:01:19","guid":{"rendered":"http:\/\/c-for-dummies.com\/blog\/?p=1216"},"modified":"2015-02-14T10:35:29","modified_gmt":"2015-02-14T18:35:29","slug":"finding-the-path_max","status":"publish","type":"post","link":"https:\/\/c-for-dummies.com\/blog\/?p=1216","title":{"rendered":"Finding the PATH_MAX"},"content":{"rendered":"

Your code may be compiled on a PC, Mac, Linux system, or even some microcontroller. In each case, it helps to know the environment before you code. You can guess, but it’s better to use the defined constants — if they’re available to you.
\n
\nWhat do you do when a constant isn’t available? Actually, what’s more important is being able to check whether or not a constant exists. To manage that feat, you use the preprocessor directives: #ifdef<\/code>, #else<\/code>, and #endif<\/code>.<\/p>\n

If you’re just starting out with C coding, you probably haven’t used preprocessor directives beyond #include<\/code> and the occasional #define<\/code>. The if-else<\/em> series of directives are easy to understand, providing you have a general concept of the if-else<\/em> programming thing.<\/p>\n

As a real-life example, consider the constant PATH_MAX<\/code>. It’s determines how many characters are allowed in a full pathname. The value differs between the various operating systems, so it’s best to use PATH_MAX<\/code> to set the buffer size for pathnames, as opposed to just guessing.<\/p>\n

To confirm that the PATH_MAX<\/code> constant is defined, use the #ifdef<\/code> directive:<\/p>\n

#ifdef PATH_MAX<\/code><\/pre>\n
When PATH_MAX<\/code> is defined, the statements following #ifdef<\/code> are compiled.<\/p>\n
When PATH_MAX<\/code> isn’t defined, the #else<\/code> directive takes over. The statements following #else<\/code> are compiled when PATH_MAX<\/code> is undefined.<\/p>\n
The #endif<\/code> directive closes the decisions structure. It’s traditionally followed by a comment identifying the constant.<\/p>\n
The following code represents a real-life example of testing for the PATH_MAX<\/code> constant, which should be defined in the limits.h<\/code> header file:<\/p>\n
\r\n#include <stdio.h>\r\n#include <limits.h>\r\n\r\nint main()\r\n{\r\n\r\n#ifdef PATH_MAX\r\n    printf(\"PATH_MAX is defined as %d.\\n\",PATH_MAX);\r\n#else\r\n    printf(\"PATH_MAX isn't defined on this system.\\n\");\r\n#endif \/* PATH_MAX *\/<\/span>\r\n\r\n    return(0);\r\n}<\/pre>\n
When the PATH_MAX<\/code> variable is defined, the first printf()<\/em> statement is compiled, otherwise the second one is compiled. Remember, preprocessor directives don’t execute when the program runs; they simply tell the compiler which part of the code to include in the final program.<\/p>\n
Here’s the output for my Macintosh:<\/p>\n
PATH_MAX is defined as 1024.<\/code><\/pre>\n
Here’s the output on my PC:<\/p>\n
PATH_MAX is defined as 260.<\/code><\/pre>\n
The differing values justify why using a constant like PATH_MAX<\/code> is important. The alternative would be to guess and specify a “safe” value for the constant. That’s a valid option only when you’ve tried testing for a constant as shown in this Lesson’s sample code.<\/p>\n","protected":false},"excerpt":{"rendered":"
And how to deal with the situation when a constant isn’t defined. Continue reading →<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[2],"tags":[],"class_list":["post-1216","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\/1216","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=1216"}],"version-history":[{"count":3,"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=\/wp\/v2\/posts\/1216\/revisions"}],"predecessor-version":[{"id":1224,"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=\/wp\/v2\/posts\/1216\/revisions\/1224"}],"wp:attachment":[{"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=1216"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=1216"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=1216"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}