Bug 23700 – ImportC: Missing examples of ImportC leveraging CTFE

When compiling the test with `gcc -std=c11 -fsyntax-only` compilable/test22842.c:64:24: error: expression in static assertion is not constant 64 | _Static_assert(mint1() == -1, "1"); | ~~~~~~~~^~~~~ compilable/test22842.c: In function ‘mint3’: compilable/test22842.c:80:18: warning: cast from pointer to integer of different size [-Wpointer-to-int-cast] 80 | unsigned x = (unsigned)(p) & 1; | ^ Test content: ``` // https://issues.dlang.org/show_bug.cgi?id=22876 int mint1() { int a = 0; // dmd gives 1, other compilers -1 // bug disappears if the parentheses around (a) are removed return - (a) - 1; } _Static_assert(mint1() == -1, "1"); ```

Another failing test: compilable/test23031.c:9:25: error: expression in static assertion is not constant 9 | _Static_assert("\x1"[0] == 1, "5"); | ~~~~~~~~~^~~~ compilable/test23031.c:10:26: error: expression in static assertion is not constant 10 | _Static_assert("\x20"[0] == 0x20, "6"); | ~~~~~~~~~~^~~~~~~ compilable/test23031.c:11:27: error: expression in static assertion is not constant 11 | _Static_assert("\x020"[0] == 0x20, "7"); | ~~~~~~~~~~~^~~~~~~ compilable/test23031.c:12:28: error: expression in static assertion is not constant 12 | _Static_assert("\x0020"[0] == 0x20, "8"); | ~~~~~~~~~~~~^~~~~~~ compilable/test23054.c:23:25: error: expression in static assertion is not constant 23 | _Static_assert(test1(1) == 2, "1"); | ~~~~~~~~~^~~~ compilable/test23054.c:24:25: error: expression in static assertion is not constant 24 | _Static_assert(test2(1) == 0, "2"); | ~~~~~~~~~^~~~ ``` /* https://issues.dlang.org/show_bug.cgi?id=23031 */ _Static_assert(sizeof("\x1") == 2, "1"); _Static_assert(sizeof("\x20") == 2, "2"); _Static_assert(sizeof("\x020") == 2, "3"); _Static_assert(sizeof("\x0020") == 2, "4"); _Static_assert("\x1"[0] == 1, "5"); _Static_assert("\x20"[0] == 0x20, "6"); _Static_assert("\x020"[0] == 0x20, "7"); _Static_assert("\x0020"[0] == 0x20, "8"); ```

Many more _Static_assert tests that fail with gcc, but pass with dmd. compilable/testcstuff1.c:113:25: error: expression in static assertion is not constant 113 | _Static_assert(f1(4, 2) == 7, "ok"); | ~~~~~~~~~^~~~ compilable/testcstuff1.c:131:22: error: expression in static assertion is not constant 131 | _Static_assert(s1(3) == 10, "s1(3) == 10"); | ~~~~~~^~~~~ compilable/testcstuff1.c:139:22: error: expression in static assertion is not constant 139 | _Static_assert(s2(3) == 10, "s2(3) == 10"); | ~~~~~~^~~~~ compilable/testcstuff1.c:150:22: error: expression in static assertion is not constant 150 | _Static_assert(s3(3) == 10, "s3(3) == 10"); | ~~~~~~^~~~~ compilable/testcstuff1.c:163:22: error: expression in static assertion is not constant 163 | _Static_assert(s4(1) == 1, "s4(1) == 1"); | ~~~~~~^~~~~ compilable/testcstuff1.c:164:22: error: expression in static assertion is not constant 164 | _Static_assert(s4(3) == 10, "s4(3) == 10"); | ~~~~~~^~~~~ compilable/testcstuff1.c:165:22: error: expression in static assertion is not constant 165 | _Static_assert(s4(5) == 11, "s4(5) == 11"); | ~~~~~~^~~~~ compilable/testcstuff1.c:175:22: error: expression in static assertion is not constant 175 | _Static_assert(s5(3) == 4, "s5(3) == 4"); | ~~~~~~^~~~ compilable/testcstuff1.c:176:22: error: expression in static assertion is not constant 176 | _Static_assert(s5(4) == 5, "s5(4) == 5"); | ~~~~~~^~~~

This is somewhat documented on https://dlang.org/spec/importc.html#ctfe Perhaps some examples of what ImportC can do vs. GCC.

Indeed, CTFE is an ImportC extension. It's very useful for writing test cases like these.

(In reply to Walter Bright from comment #4) > Indeed, CTFE is an ImportC extension. It's very useful for writing test > cases like these. Updated title, the page really should give some quick examples.

*** This issue has been marked as a duplicate of issue 23694 ***