| Issue |
181747
|
| Summary |
-Wconstant-conversion missing out-of-range integral constant in NTTP and template initialization
|
| Labels |
new issue
|
| Assignees |
|
| Reporter |
Stee-T
|
**Description**
`-Wconstant-conversion` does not emit a diagnostic when an integer constant outside the representable range of an integral is used as a non-type template parameter (NTTP) value.
This includes both default template arguments and explicit template arguments.
Although the program is well-formed C++ (the value is reduced modulo the destination type), the same conversion *does* trigger a diagnostic in normal variable initialization. This suggests inconsistent diagnostic handling for identical constant conversions.
**1. Default non-type template parameter**
```cpp
#include <cstdint>
template < uint8_t N = 400 >
struct TOk {};
```
**Actual behavior**
No diagnostic is emitted with ```-Wconstant-conversion```
**Expected behavior**
A diagnostic indicating that the constant value cannot be represented in `uint8_t` (even though the program remains well-formed and the value is reduced modulo the type).
**2. Explicit template argument**
```cpp
template<unsigned char N>
struct S {};
S<400> s; // no warning
```
**3. Control example — equivalent initialization does warn**
```cpp
unsigned char x = 400; // warning emitted here
```
This shows the same constant conversion is diagnosed in a normal initialization context but not when performed as part of template argument checking.
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