When a file is passed to gcc through stdin, gcc won't print any diagnostics carets for the passed file. Example: // test.c int main(int argc, char **argv) { return 0; } When test.c is passed to gcc through stdin, the following is printed: $ cat test.c | gcc -Wall -Wextra -xc - <stdin>: In function ‘main’: <stdin>:1:14: warning: unused parameter ‘argc’ [-Wunused-parameter] <stdin>:1:27: warning: unused parameter ‘argv’ [-Wunused-parameter] (Note that forcing the -fdiagnostics-show-caret option doesn't change anything) I would have expected the same output as when the file is passed to gcc as an argument: $ gcc -Wall -Wextra test.c test.c: In function ‘main’: test.c:1:14: warning: unused parameter ‘argc’ [-Wunused-parameter] 1 | int main(int argc, char **argv) | ~~~~^~~~ test.c:1:27: warning: unused parameter ‘argv’ [-Wunused-parameter] 1 | int main(int argc, char **argv) | ~~~~~~~^~~~
This is done on purpose. It is based on the original file, rather than the preprocessed source or otherwise. With stdin, there is no original file being referenced.
That's too bad. For my use case it would be more efficient if I passed the file directly to gcc through stdin. There is really no way to change this, maybe through an option? With clang this works as expected. The same diagnostics are printed independent of whether the file was passed through stdin or as a command-line argument.
In my opinion the current behavior is somehow inconsistent since the carets are displayed for included files. Example: // test.cpp #include <coroutine> int main(int argc, char **argv) { return 0; } $ cat test.cpp | g++ -Wall -Wextra -xc++ - In file included from <stdin>:1: /usr/lib/gcc/x86_64-pc-linux-gnu/10.2.0/include/g++-v10/coroutine:295:2: error: #error "the coroutine header requires -fcoroutines" 295 | #error "the coroutine header requires -fcoroutines" | ^~~~~ <stdin>: In function ‘int main(int, char**)’: <stdin>:3:14: warning: unused parameter ‘argc’ [-Wunused-parameter] <stdin>:3:27: warning: unused parameter ‘argv’ [-Wunused-parameter]