casaroli commented on issue #21467:
URL: https://github.com/apache/nuttx/issues/21467#issuecomment-6649291313
@anchao The cases we listed are not programmer errors. They are all valid C:
the format and the arguments agree, as in your first Rust example.
```c
char buf[301];
sprintf(buf, "%300d", 1); /* the width fits the buffer, and 556
bytes are written */
printf("%a|%s\n", 1.0, "x"); /* %a is in C99 and takes a double; %s
gets a wrong pointer on arm64 */
printf("%Lf|%s\n", 1.5L, "x"); /* %Lf takes a long double, and it is
read as a double */
```
The compiler will not solve these, because there is nothing wrong in the
code. GCC 13.2 with `-Wall -Wextra -Wformat=2 -Wformat-overflow=2` and Clang 22
with `-Wall -Wextra -Wformat=2` compile them with no warning. The bug is in
`printf`, and no developer, experienced or not, can avoid it without knowing
the code of `printf`.
We agree on the rest. A wrong type for a conversion, an unknown conversion
and a truncated format are programmer errors, and the same compilers warn about
them with `-Wall`. We spend no flash on the wrong types, and the other two move
behind an option.
So this is the boundary: if the compiler accepts the call, it is correct
usage and `printf` must handle it. If the compiler warns, it is wrong usage.
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