Question

I have a buffer and I don’t want the user to enter more characters than the buffer can hold (to avoid a buffer overrun).

I am using scanf and have done like this:

char buffer[30] = {'\0'};
scanf("%30s", buffer);

However, I know I am protected if the user enters more than 30. However, if the user enters more than 30, will the buffer be null terminated?

Answer 1

scanf() with a “%s” conversion specifier adds a terminating null character to the buffer.

But, you’re asking for 30 characters, which really means 31 and only have space for 30. You should use a maximum field width of 29.

char buffer[30] = {'\0'};
scanf("%29s", buffer);

Also note that the conversion specifier "%c" works pretty much like "%s", but does not add the terminating null character and does not discard space from the input. Depending on what you expect, it might be better than using “%s”.

char buffer[30] = {'\0'};
scanf("%29c", buffer);
buffer[29] = '\0';