{"id":5711,"date":"2023-01-21T00:01:44","date_gmt":"2023-01-21T08:01:44","guid":{"rendered":"https:\/\/c-for-dummies.com\/blog\/?p=5711"},"modified":"2023-01-07T11:11:53","modified_gmt":"2023-01-07T19:11:53","slug":"not-every-compiler-likes-your-code","status":"publish","type":"post","link":"https:\/\/c-for-dummies.com\/blog\/?p=5711","title":{"rendered":"Not Every Compiler Likes Your Code"},"content":{"rendered":"

You would think that the various C compilers deal with C code in the same manner. After all, they adhere to the same C standards, right? This compatibility makes it possible to compile and cleanly build C programs regardless of which compiler you use, right? Well, maybe not.
\n
\nI recently discovered that I technique I use for my C programs works well in the LLVM clang<\/em> compiler, but really ticks off gcc<\/em> in Linux. Here is the code:<\/p>\n

2022_01_21-Lesson.c<\/a><\/h3>\n
\r\n#include <stdio.h>\r\n\r\nint main()\r\n{\r\n    const int size = 5;\r\n    int data[size] = {\r\n        5, 8, 2, 6, 9\r\n    };\r\n    int x = 0;\r\n\r\n    while( x<size )\r\n        printf(\"%d\\n\",data[x++]);\r\n\r\n    return(0);\r\n}<\/pre>\n
At Line 5, I set variable size<\/code> as a constant to be used throughout the code. It represents the number of elements in the data[]<\/code> array. I could just declare the array without a size value, in which case the compiler figures out the number of elements. But I use the element count as the while<\/em> loop’s condition at Line 11. This approach is more readable, plus it avoids having a “magic number” in the code that other programmers may not readily recognize.<\/p>\n
The clang<\/em> compiler has no issues with my using a constant to declare the data[]<\/code> array’s size.<\/p>\n
On the Macintosh, the gcc<\/em> compiler (which is probably aliased to clang<\/em>) has no issues either.<\/p>\n
In Linux, however, the gcc<\/em> compiler is hostile toward this approach. It spews out this error:<\/p>\n
error: variable-sized object may not be initialized<\/code><\/p>\n
I use this “variable-sized object” initialization in a lot of my code. Imagine how annoyed I was when I was using an alien system with only gcc<\/em> available and this error puked all over my screen. (The error message is followed by a series of warnings, one for each array element.)<\/p>\n
My frustration with this “error” is not only do other compilers not think it’s an issue, but that gcc<\/em> also lets you declare an array with a variable size. The key is not to initialize it. So the following statement is okee-doke:<\/p>\n
int data[size];<\/code><\/p>\n
You can then manually assign all the element values.<\/p>\n
Some of the feedback I’ve read on the Internet states that it works, but not on a variable-length array (VLA). But data[]<\/code> isn’t a VLA. In fact, even if I declare the array const<\/em>, gcc<\/em> gets angry with the same intensity.<\/p>\n
I’m at a loss.<\/p>\n
I suppose for compatibility’s sake, I must stop using a constant to initialize an array. I feel the construction is less readable, especially because the constant (for the array’s size) is used elsewhere in the function, but if I strive to write code compatible with the major compilers, it’s a sacrifice I must make.<\/p>\n","protected":false},"excerpt":{"rendered":"
Imagine my horror at discovering that the clang<\/em> compiler lets me do something that the gcc<\/em> compiler finds offensive. 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-5711","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\/5711","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=5711"}],"version-history":[{"count":4,"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=\/wp\/v2\/posts\/5711\/revisions"}],"predecessor-version":[{"id":5719,"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=\/wp\/v2\/posts\/5711\/revisions\/5719"}],"wp:attachment":[{"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=5711"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=5711"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=5711"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}