The C23 standard is only partially implemented on a few compilers. To ensure that you can build C23 programs, you must obtain the latest compiler version from your distro’s package manager. Even then, not all the C23 capabilities may be available.
\n
\nTwo things are required to test for C23 compatibility.<\/p>\n
First, the compiler standard switch, also called the flavor<\/em>, must be set to C23. This switch is All C compilers have a default configuration. For most of today’s compilers, it’s the C17 standard. To use another standard, such as C99, you must compile with the switch I’m using clang<\/em> as my compiler above, though you can use gcc<\/em> or whichever compiler you prefer; the switch is identical. The file The Second, you must test the C version number held in the The following code outputs the The printf()<\/em> statement outputs the value of the Here’s a sample run when compiled under clang<\/em> without the If I use the I find this output questionable, as this same configuration is unable to build the sample code from last week’s Lesson<\/a>.<\/p>\n Here is the output under clang-15<\/em> without the Here is the output under clang-15<\/em> with the In this configuration, the C23 test program from last week’s Lesson builds with no errors.<\/p>\n For the purposes of moving forward, ensure that you not only have a C compiler that not only accepts the In next week’s Lesson<\/a>, I cover the way C23 deals with binary integers.<\/p>\n","protected":false},"excerpt":{"rendered":" The C23 standard is only partially implemented on a few compilers. To ensure that you can build C23 programs, you must obtain the latest compiler version from your distro’s package manager. Even then, not all the C23 capabilities may be … Continue reading ‑std=nnn<\/em><\/code> where nnn<\/em> is the C standard to use for compiling.<\/p>\n‑std=c99<\/code>. For C23, here is the command line format:<\/p>\nclang -std=c99 source.c<\/code><\/p>\nsource.c<\/code> is built adhering to only the C99 standard. A programmer may want to assert this standard for compatibility with an older system.<\/p>\n-std=c2x<\/code> switch implements the C23 standard. Don’t use -std=c23<\/code> (c23<\/code> instead of c2x<\/code>), which isn’t recognized — yet.<\/p>\n__STDC_VERSION__<\/code> defined constant<\/a>. See those double underscores? They’re used internally to flag special defined constants.<\/p>\n__STDC_VERSION__<\/code> value and tests for C23 compatibility.<\/p>\n2023_12_23-Lesson.c<\/a><\/h3>\n
\r\n#include <stdio.h>\r\n\r\nint main()\r\n{\r\n printf(\"C version %ld\\n\",__STDC_VERSION__);\r\n if( __STDC_VERSION__ >= 202000 )\r\n puts(\"C23 features available\");\r\n else\r\n puts(\"C23 features unavailable\");\r\n\r\n return 0;\r\n}<\/pre>\n__STDC_VERSION__<\/code> defined constant. The if<\/em> test compares this value with 202000, which seems to be the current value for C23 implementation across various compilers.<\/p>\n-std=c2x<\/code> switch:<\/p>\nC version 201710
\nC23 features unavailable<\/code><\/p>\n-std=c2x<\/code> switch on the regular clang<\/em> compiler, I get this output:<\/p>\nC version 202000
\nC23 features available<\/code><\/p>\n-std=c2x<\/code> switch:<\/p>\nC version 201710
\nC23 features unavailable<\/code><\/p>\n-std=c2x<\/code> switch:<\/p>\nC version 201710
\nC23 features available<\/code><\/p>\n-std=c2x<\/code> switch, but can build C23 code. Apparently the value of __STDC_VERSION__<\/code> isn’t reliable. I’m unaware of any other tests, other than just running C23 code to see whether it builds without any errors.<\/p>\n