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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.)
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- that function cannot fail.
- its return value is inconsequential; that is, it does not indicate an error.
- it is one of a handful of functions whose return values are not traditionally checked.
These functions are listed in the following table:
Functions for which Return Values Need Not Be Checked
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The return value of a call to fprintf() or one of its variants (vfprintf(), wfprintf(), vwfprintf()) or one of the file output functions fputc(), fputwc(), fputs(), fputws() may may be ignored if the output is being directed to stdout or stderr . Otherwise, the return value must be checked.
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| [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] |
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