{"id":1221,"date":"2015-02-28T00:01:32","date_gmt":"2015-02-28T08:01:32","guid":{"rendered":"http:\/\/c-for-dummies.com\/blog\/?p=1221"},"modified":"2015-03-07T08:03:34","modified_gmt":"2015-03-07T16:03:34","slug":"fetching-the-current-path","status":"publish","type":"post","link":"https:\/\/c-for-dummies.com\/blog\/?p=1221","title":{"rendered":"Fetching the Current Path"},"content":{"rendered":"

The C library hosts many file and directory management functions. They’re all pretty standard, no matter which operating system you use. What isn’t standard, however, is the size of a pathname. That value plays an important role if you’re to properly allocate memory to store directory information.
\n
\nIn my book, Beginning Programming with C For Dummies<\/em>, I did not properly allocate memory for a path. Nope, I just guessed. In Exercises 23-5<\/a> and 23-6<\/a> I use the immediate value 255 for a buffer to hold the current directory.<\/p>\n

An option better than just guessing is to use the PATH_MAX<\/code> constant. It’s defined in the limits.h<\/code> header file.<\/p>\n

One of the reasons I didn’t use PATH_MAX<\/code> in my book is that it’s not available on all systems, which would require further explanation and a solution similar to what’s presented in this Lesson.<\/p><\/blockquote>\n

In the following code, PATH_MAX<\/code> is used to create storage for the current working directory. The code uses preprocessor directives (covered in last week’s Lesson<\/a>) to determine whether PATH_MAX<\/code> exists. If so, its value is used, otherwise the pulled-it-out-of-thin-air value of 255 is set.<\/p>\n

\r\n#include <stdio.h>\r\n#include <stdlib.h>\r\n#include <limits.h>\r\n#include <unistd.h>\r\n\r\n#ifndef PATH_MAX\r\n#define PATH_MAX 255\r\n#endif \/* PATH_MAX *\/<\/span>\r\n\r\nint main()\r\n{\r\n    char *path;\r\n\r\n\/* Allocate memory for the current path *\/<\/span>\r\n    path = (char *)malloc(PATH_MAX);\r\n    if( path == NULL)\r\n    {\r\n        perror(\"Unable to allocate memory\");\r\n        exit(1);\r\n    }\r\n\r\n\/* Fetch and display directory pathname *\/<\/span>\r\n    getcwd(path,PATH_MAX);\r\n    printf(\"Current directory is '%s'\\n\",path);\r\n\r\n    return(0);\r\n}<\/pre>\n
This code uses malloc()<\/em> to allocate storage for the current working directory’s path. That way an overflow won’t occur and I’m not wasting more space than is necessary.<\/p>\n
Here’s sample output:<\/p>\n
Current directory is '\/Users\/dang\/prog\/c\/blog'<\/code><\/pre>\n
Seeing how ancient the C language is getting, it’s easy to understand that PATH_MAX<\/code> isn’t the only constant available to check how large the current path buffer can be. Another constant, MAXPATHLEN<\/code>, is available. It’s defined in the sys\/param.h<\/code> header file.<\/p>\n
In next week’s Lesson<\/a>, I’ll compare the PATH_MAX<\/code> and MAXPATHLEN<\/code> constants to see whether they differ. I’ll also present an alternative to this Lesson’s code that uses only one statement to perform the same task.<\/p>\n","protected":false},"excerpt":{"rendered":"
Which directory is the program using? 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-1221","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\/1221","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=1221"}],"version-history":[{"count":7,"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=\/wp\/v2\/posts\/1221\/revisions"}],"predecessor-version":[{"id":1261,"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=\/wp\/v2\/posts\/1221\/revisions\/1261"}],"wp:attachment":[{"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=1221"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=1221"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=1221"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}