https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69229
Bug ID: 69229
Summary: missing type information in diagnostics about type
mismatch in conditional expressions
Product: gcc
Version: 6.0
Status: UNCONFIRMED
Severity: minor
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: msebor at gcc dot gnu.org
Target Milestone: ---
The C front end issues diagnostics for invalid implicit conversions in various
contexts, such as in the conditional expressions below. However, since the
diagnostic doesn't mention the types of the incompatible operands, it can be
non-trivial to determine what exactly is causing the incompatibility and what
the most appropriate way to resolve it is when the operands are declared far
from the expression (such in a header), the result of a computation, or hidden
behind layers of macros. (Depending on their types, it might be appropriate to
explicitly cast one operand to the type of the other, or both to some other
type.)
It would be useful if the C front end mentioned the types of the operands in
these diagnostics, similar to how other compilers do it.
$ cat a.c && ~/bin/gcc-5.1.0/bin/gcc -std=c11 -S -o/dev/null a.c
void* foo (int *p, float *q) {
return 1 ? p : q;
}
void* bar (int *p, int i) {
return 1 ? p : i;
}
struct S { int i; };
void* baz (int i, struct S s) {
return 1 ? i : s;
}
a.c: In function ‘foo’:
a.c:2:18: warning: pointer type mismatch in conditional expression
return 1 ? p : q;
^
a.c: In function ‘bar’:
a.c:6:18: warning: pointer/integer type mismatch in conditional expression
return 1 ? p : i;
^
a.c: In function ‘baz’:
a.c:11:18: error: type mismatch in conditional expression
return 1 ? i : s;
^
For example, g++ issues the following:
a.c: In function ‘void* foo(int*, float*)’:
a.c:2:20: error: conditional expression between distinct pointer types ‘int*’
and ‘float*’ lacks a cast [-fpermissive]
return 1 ? p : q;
^
a.c: In function ‘void* bar(int*, int)’:
a.c:6:14: error: operands to ?: have different types ‘int*’ and ‘int’
return 1 ? p : i;
~~^~~~~~~
a.c: In function ‘void* baz(int, S)’:
a.c:11:14: error: operands to ?: have different types ‘int’ and ‘S’
return 1 ? i : s;
~~^~~~~~~
And Clang (in C mode):
a.c:2:14: warning: pointer type mismatch ('int *' and 'float *')
[-Wpointer-type-mismatch]
return 1 ? p : q;
^ ~ ~
a.c:6:14: warning: pointer/integer type mismatch in conditional expression
('int *' and 'int') [-Wconditional-type-mismatch]
return 1 ? p : i;
^ ~ ~
a.c:11:14: error: incompatible operand types ('int' and 'struct S')
return 1 ? i : s;
^ ~ ~
2 warnings and 1 error generated.
