https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95445
--- Comment #4 from Florian Weimer <fw at gcc dot gnu.org> --- Patch posted: [PATCH] c: Implement -Wdeprecated-non-prototype <https://inbox.sourceware.org/gcc-patches/87plmwyue3....@oldenburg.str.redhat.com/> This is what the new warning produces for the input from the description: t.c: In function ‘f0’: t.c:5:10: warning: ISO C23 does not allow arguments for function ‘strchr’ declared without parameters [-Wdeprecated-non-prototype] 5 | return strchr (s, 'x'); // no warning (okay) | ^~~~~~ t.c:1:7: note: declared here 1 | char* strchr (); | ^~~~~~ t.c: In function ‘f1’: t.c:10:10: warning: ISO C23 does not allow arguments for function ‘strchr’ declared without parameters [-Wdeprecated-non-prototype] 10 | return strchr (s, "y"); // warning (good) | ^~~~~~ t.c:1:7: note: declared here 1 | char* strchr (); | ^~~~~~ t.c:10:21: error: passing argument 2 of ‘strchr’ makes integer from pointer without a cast [-Wint-conversion] 10 | return strchr (s, "y"); // warning (good) | ^~~ | | | char * t.c:1:7: note: expected ‘int’ but argument is of type ‘char *’ 1 | char* strchr (); | ^~~~~~ t.c: In function ‘h’: t.c:17:3: warning: ISO C23 does not allow arguments for function ‘g’ declared without parameters [-Wdeprecated-non-prototype] 17 | g (1); // (presumably) okay, f's type is 'void (int)' | ^ t.c:13:6: note: declared here 13 | void g (); | ^ t.c:18:3: warning: ISO C23 does not allow arguments for function ‘g’ declared without parameters [-Wdeprecated-non-prototype] 18 | g ("foo"); // should be diagnosed | ^ t.c:13:6: note: declared here 13 | void g (); | ^ t.c:19:3: warning: ISO C23 does not allow arguments for function ‘g’ declared without parameters [-Wdeprecated-non-prototype] 19 | g (1, "bar"); // ditto | ^ t.c:13:6: note: declared here 13 | void g (); | ^
