https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112463
Bug ID: 112463 Summary: ternary operator / -Wsign-compare inconsistency Product: gcc Version: 13.2.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: c Assignee: unassigned at gcc dot gnu.org Reporter: vincent-gcc at vinc17 dot net Target Milestone: --- -Wsign-compare is described in the man page as follows: -Wsign-compare Warn when a comparison between signed and unsigned values could produce an incorrect result when the signed value is converted to unsigned. In C++, this warning is also enabled by -Wall. In C, it is also enabled by -Wextra. But it can emit a warning even in the absence of comparisons between signed and unsigned values. For instance, it can appear due to the 2nd and 3rd operands of the ternary operator (these operands are not compared, just selected from the value of the first operand). This affects the warning output by -Wextra. Consider the following C code: #include <stdio.h> int main (void) { for (int c = -1; c <= 1; c++) { long long i = c == 0 ? 0LL : (c >= 0 ? 1U : -1), j = c >= 0 ? (c == 0 ? 0LL : 1U) : -1; printf ("i = %lld\nj = %lld\n", i, j); } return 0; } (which shows that the ternary operator is not associative due to type conversions). With -Wextra, I get: ternary-op.c: In function ‘main’: ternary-op.c:7:43: warning: operand of ‘?:’ changes signedness from ‘int’ to ‘unsigned int’ due to unsignedness of other operand [-Wsign-compare] 7 | i = c == 0 ? 0LL : (c >= 0 ? 1U : -1), | ^~ But the "-Wsign-compare" is incorrect as there are no comparisons between signed and unsigned values. Only -Wsign-conversion should trigger a warning.