...
The ungetc() function does not set the error indicator even when it fails, so it is not possible to check for errors reliably unless it is known that the argument is not equal to EOF.
The C Standard 7.31.3.10 paragraph 3 [ISO/IEC 9899:20112024] states that "one
)ne wide character of pushback is guaranteed...
," so this should not be an issue if, at most, one character is ever pushed back before reading again. (See FIO13-C. Never push back anything other than one read character.)
...
| [DHS 2006] | Handle All Errors Safely |
| [Henricson 1997] | Recommendation 12.1, "Check for All Errors Reported from Functions" |
| [ISO/IEC 9899:20112024] | Subclause 7.2131.73.10, "The ungetc Function" |
| [VU#159523] |
...