{"id":4711,"date":"2021-04-24T00:01:16","date_gmt":"2021-04-24T07:01:16","guid":{"rendered":"https:\/\/c-for-dummies.com\/blog\/?p=4711"},"modified":"2021-04-16T15:55:33","modified_gmt":"2021-04-16T22:55:33","slug":"how-big-is-your-bufsiz","status":"publish","type":"post","link":"https:\/\/c-for-dummies.com\/blog\/?p=4711","title":{"rendered":"How Big is Your BUFSIZ?"},"content":{"rendered":"

When my code requires a random odd buffer, I generally assign it a given size in some holy computer value: 16, 32, 64, and so on. But a defined constant exists, BUFSIZ<\/code>, that can also be used to set a buffer size safely and consistently on all C compilers.
\n
\nJust to get it out of the way, it vexes me to no end that the BUFSIZ<\/code> constant lacks an E<\/code> in its name. Seriously.<\/p>\n

The BUFSIZ<\/code> defined constant is declared in the stdio.h<\/code> header file as a default buffer size. Specifically, it’s the size of the buffer used by the setbuf()<\/em> function, which was covered in this blog post<\/a>. Here is the code from the post:<\/p>\n

2021_04_24-Lesson-a.c<\/a><\/h3>\n
\r\n#include <stdio.h>\r\n\r\nint main()\r\n{\r\n    char buffer[BUFSIZ];\r\n\r\n    \/* setup the buffer *\/<\/span>\r\n    setbuf(stdout,buffer);\r\n\r\n    puts(\"Hold it!\");\r\n    puts(\"Hold it!\");\r\n    puts(\"Go!\");\r\n    getchar();\r\n    puts(\"Thank you.\");\r\n\r\n    return(0);\r\n}<\/pre>\n
Streaming C functions use BUFSIZ<\/code> for their operations, as does setbuf()<\/em> shown above. The code changes output streaming, holding it in buffer[]<\/code> until input is received from the getchar()<\/em> function at Line 13. The program’s output then appears all at once. Refer to the earlier post for more details, but my purpose here is to discuss BUFSIZ<\/code>.<\/p>\n
You can borrow the BUFSIZ<\/code> defined constant for use in declaring your code’s buffer size, especially when working with input and output. Still, curiosity gets the best of me: How big is BUFSIZ<\/code>? What is its defined value?<\/p>\n
You could plow through stdio.h<\/code> (and all its included header files) to locate the BUFSIZ<\/code> declaration, but instead just run the following code:<\/p>\n
2021_04_24-Lesson-b.c<\/a><\/h3>\n
\r\n#include <stdio.h>\r\n\r\nint main()\r\n{\r\n    printf(\"On this machine, the BUFSIZ buffer is set to %d bytes\\n\",\r\n            BUFSIZ\r\n          );\r\n\r\n    return(0);\r\n}<\/pre>\n
Because BUFSIZ<\/code> is assigned an int<\/em>, I use the %d<\/code> placeholder in the printf()<\/em> statement to output the value.<\/p>\n
Here’s what appears on my Mac: <\/p>\n
On this machine, the BUFSIZ buffer is set to 1024 bytes<\/code><\/p>\n
A 1K buffer seems nice, but here’s the output for Ubuntu Linux:<\/p>\n
On this machine, the BUFSIZ buffer is set to 8192 bytes<\/code><\/p>\n
My Linux distro sets a buffer size of 8K, or 8,192 bytes. Interesting — and I don’t know why.<\/p>\n
Here’s the output from MinGW using Code::Blocks in Windows:<\/p>\n
On this machine, the BUFSIZ buffer is set to 512 bytes<\/code><\/p>\n
Whoa.<\/p>\n
While no consistent value seems to be set for the various compilers, the point is that BUFSIZ<\/code> is available and ready for use when you quickly need a buffer for streaming input and output. Whether it be large or small, it’s what the compiler designers felt would be adequate for the given environment.<\/p>\n
Another point!<\/p>\n
This Lesson demonstrates the value of defined constants: The name BUFSIZ<\/code> is consistent and available to all compilers, yet each compiler sets a different value. The same concept applies to typedefs<\/em>, providing cross-platform consistency without the programmer (you) needing to worry about or research the specifics.<\/p>\n","protected":false},"excerpt":{"rendered":"
The BUFSIZ<\/code> defined constant provides a handy way to create a buffer of a given size. But what’s the size? 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-4711","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\/4711","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=4711"}],"version-history":[{"count":9,"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=\/wp\/v2\/posts\/4711\/revisions"}],"predecessor-version":[{"id":4735,"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=\/wp\/v2\/posts\/4711\/revisions\/4735"}],"wp:attachment":[{"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=4711"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=4711"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=4711"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}