{"id":2877,"date":"2017-12-30T00:01:53","date_gmt":"2017-12-30T08:01:53","guid":{"rendered":"http:\/\/c-for-dummies.com\/blog\/?p=2877"},"modified":"2017-12-23T09:48:59","modified_gmt":"2017-12-23T17:48:59","slug":"the-size_t-variable-type","status":"publish","type":"post","link":"https:\/\/c-for-dummies.com\/blog\/?p=2877","title":{"rendered":"The size_t<\/em> Variable Type"},"content":{"rendered":"

The C language has its basic variable types: char<\/em>, int<\/em>, float<\/em>, double<\/em>, struct<\/em>, and that oddball newbie _Bool<\/em>. Anything else you see as a “variable” is probably a convenient shortcut manufactured by using a typedef<\/em> statement. Some of these typedef<\/em> variables are faily standard, including the most common one, size_t<\/em>.
\n
\nThe typedef<\/em> operator creates a convenient shortcut for a variable type. It’s similar to the #define<\/code> preprocessor directive in that it’s valid only in the code where it’s used.<\/p>\n

Most frequently, typedef<\/em> creates shortcuts for structure variables, but many header files use typedef<\/em> to create special names for specific variable types, such as size_t<\/em>. Specifically, the size_t<\/em> variable type is related to the sizeof<\/em> operator, which returns the size of a memory object in bytes.<\/p>\n

In the original K&R book, a byte<\/em> is defined as the size of a char<\/em> variable: One byte of memory equals one char<\/em>-sized value. When the sizeof<\/em> operator returns 4, you know that the object occupies 4 bytes (char<\/em>s) of memory.<\/p>\n

When Drs. Kernighan and Ritchie updated their book to cover ANSI C, they introduced the size_t<\/em> variable as the type of value returned from the sizeof<\/em> operator. It’s defined, or typedef<\/em>‘d, as an unsigned int<\/em> value, usually an unsigned long<\/em>. The value represents the size (in bytes) of a chunk of memory. So, whenever you see the size_t<\/em> variable in a function prototype, it means that the function somehow deals with a chunk of memory.<\/p>\n

For example, the malloc()<\/em> function uses a size_t<\/em> argument to set aside a chunk of memory:<\/p>\n

void * malloc(size_t size);<\/code><\/p>\n

The size_t<\/em> value also appears in some string function prototypes:<\/p>\n

size_t strlen(const char *s);<\/code><\/p>\n

The strlen()<\/em> function returns the length of a string, which is really a value describing (almost) how many bytes (char<\/em>s) of storage the string occupies. (The value returned from strlen()<\/em> doesn’t account for the null character at the end of the string.)<\/p>\n

It’s common practice to use an int<\/em> variable when a size_t<\/em> value is specified, though this approach isn’t best. First, size_t<\/em> is an unsigned<\/em> value; you can’t have negative memory storage. Second, you must use the proper variable type with a function, lest you get into trouble.<\/p>\n

When a function calls for a size_t<\/em> variable, I recommend declaring any associated variables as size_t<\/em> values, not an int<\/em>, unsigned long<\/em>, or unsigned int<\/em>:<\/p>\n

size_t msize,mnew,and,so,on;<\/code><\/p>\n

The variables defined above are created as size_t<\/em> types.<\/p>\n

Another good practices is to use the proper placeholder in a printf()<\/em> statement to display a size_t<\/em> value. Remember, the value isn’t an int<\/em>: When you use the %d<\/code> placeholder, the compiler whines at you. That’s because the %d<\/code> placeholder represents a signed<\/em> value.<\/p>\n

In my code, I use %lu<\/code> (long unsigned<\/em>):<\/p>\n

\r\n#include <stdio.h>\r\n  \r\nint main()\r\n{\r\n    printf(\"An int uses %lu bytes of storage.\\n\",\r\n            sizeof(int)\r\n          );\r\n\r\n    return(0);\r\n}<\/pre>\n
The C99 standard established the %z<\/code> placeholder prefix for size_t<\/em> values. You postfix the %z<\/code> with a d<\/code> or u<\/code>, as in %zu<\/code> or %zd<\/code>, to properly display a size_t<\/em> value.<\/p>\n
Other typedef<\/em> values are used in various C language functions, such as the time_t<\/em> values found in time.h<\/code> functions. As with size_t<\/em>, ensure that you create time_t<\/em> variables for use with these functions. Using unsigned int<\/em> values is okay, and I’ve done so in my code, but setting the proper variable type reduces the potential for errors.<\/p>\n","protected":false},"excerpt":{"rendered":"
It’s not an official C language variable type, but it could be. 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-2877","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\/2877","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=2877"}],"version-history":[{"count":6,"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=\/wp\/v2\/posts\/2877\/revisions"}],"predecessor-version":[{"id":2892,"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=\/wp\/v2\/posts\/2877\/revisions\/2892"}],"wp:attachment":[{"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=2877"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=2877"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=2877"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}