How to use sscanf correctly and safely

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The scanf family of function cannot be used safely, especially when dealing with integers. The first case you mentioned is particularly troublesome. The standard says this:

If this object does not have an appropriate type, or if the result of
the conversion cannot be represented in the object, the behavior is
undeļ¬ned.

Plain and simple. You might think of %5d tricks and such but you’ll find they’re not reliable. Or maybe someone will think of errno. The scanf functions aren’t required to set errno.

Follow this fun little page: they end up ditching scanf altogether.

So go back to your C professor and ask them: how exactly does C99 mandate that sscanf will report errors ?

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