What does fgets do?

问题:

It is not equal:

fgets (answer, 256, stdin);

if (strncmp(answer, "sta", 4) == 0)
  printf("omg, it's equal"); 

This code is:

fgets (answer, 4, stdin);

if (strncmp(answer, "sta", 4) == 0)
  printf("omg, it's equal"); 

Why? It is because in the first, answer doesn't have \0 at the 4th place I guess (if I change it to 3 instead of 4 it works). But what does fgets do? String answer in the first is str \whitespace*253\0"? And in the second it is str\0? Thank you.

回答1:

fgets (unlike gets) includes the trailing \n corresponding to the return pressed at the end of the line. If you put 3 as the limit it truncates the string, discarding the \n.

From the manpage:

fgets() reads in at most one less than size characters from stream and stores them into the buffer pointed to by s. Reading stops after an EOF or a newline. If a newline is read, it is stored into the buffer. A terminating null byte ('\0') is stored after the last character in the buffer.