Why gets function gives a warning every time you compile a c program?

Answer 1

It is unsafe. In order to use gets() safely, you need to know how many characters you will be reading to ensure your character buffer is large enough:

char buffer[10];

while (gets (buffer) != 0) { ...process buffer... }

The above code has undefined behaviour when the number of characters read is 10 or more (you need one character for the null-terminator). This is because the character buffer, str, decays to a pointer (referencing &str[0]) and the function, gets(), cannot determine the number of characters in a buffer by its pointer alone.

The gets() function was dropped from the C standard in 2011, however some implementations still include it. To avoid the warning, use the fgets() function instead. This allows you to specify the length of your buffer and (when used correctly) prevents buffer overflow.

char buffer[10];

while (fgets (buffer, 10, stdin) != 0) { ...process buffer... }