program does not read string with the defined length in fgets()

Question

I found when I use the fgets function like so:

#include <stdio.h> #include <stdlib.h> int main(void) { char str[10]; fgets(str, 5, stdin); printf("%s", str); system("PAUSE"); return 0; }

If I input a 123456789, it will output a 1234. That's 4 characters - not the 5 I have defined in the function. What is happening to the fifth character?

edit: title updated

fifth character is null character. strings end with null termination in C language — saygins
– saygins, Commented Nov 13, 2016 at 21:20
@saygins sorry for discarding your edit, but I had a concurrent substantial edit in the works at the same time. and NULL (the preprocessor macro for the null pointer) is not the same as NUL (the null character): stackoverflow.com/questions/2911089/null-terminating-a-string — Jean-François Fabre
– Jean-François Fabre ♦, Commented Nov 13, 2016 at 21:22
see fgets (Reads at most count - 1 characters from the given file stream) — BLUEPIXY
– BLUEPIXY, Commented Nov 14, 2016 at 0:30

Jean-François Fabre · Accepted Answer · 2016-11-13 21:20:22Z

that's because since C-strings are NUL terminated, fgets takes the string terminator (\0) into account, so if you pass a 5-char buffer, it is safe.

In your code, you should do:

fgets(str, sizeof(str), stdin);

since str is an array with known size.

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