https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111421
Bug ID: 111421
Summary: constexpr not working with array subscript
Product: gcc
Version: 13.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: malekwryyy at gmail dot com
Target Milestone: ---
Created attachment 55903
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=55903&action=edit
the c program that results in the error
compiled with: -std=c2x -Wall -Wextra
When trying to subscript a constexpr array, the compiler says the expression is
not constant.
I would expect if the index is an integer literal (or a constexpr integer) then
the resulting expression should still be constant.
I tried this with -std=c2x and -std=gnu2x
// program start
typedef struct S { int i; } S;
constexpr int a = (constexpr S){.i = 3}.i; // works as expected
constexpr int b = ( &(constexpr S){.i = 3} )->i; // works as expected
constexpr int y = (constexpr int[]){3}[0]; // doesn't work. Compiler says
expression not constant
int main()
{
return 0;
}
// program end
the compiler error I get is:
<source>:7:19: error: initializer element is not constant
7 | constexpr int y = (constexpr int[]){3}[0]; // doesn't work. Compiler
says expression not constant
| ^
<source>:7:15: warning: 'y' defined but not used [-Wunused-const-variable=]
7 | constexpr int y = (constexpr int[]){3}[0]; // doesn't work. Compiler
says expression not constant
| ^
<source>:5:15: warning: 'b' defined but not used [-Wunused-const-variable=]
5 | constexpr int b = ( &(constexpr S){.i = 3} )->i; // works as expected
| ^
<source>:3:15: warning: 'a' defined but not used [-Wunused-const-variable=]
3 | constexpr int a = (constexpr S){.i = 3}.i; // works as expected
| ^
Compiler returned: 1
