CODEWITHSUNDEEP
cfgets
potato
potato

Reputation: 179

How does fgets treat enter key press?

What I am seeing is that while accepting a string - fgets takes the string till an enter key is pressed, and in the end it DOES NOT replace the enter key with \0 - rather appends \0 to the string including enter key. In comparison, gets_s takes the string till enter key is pressed and in the end - replaces the last enter key with \0.

Is this correct. Please add, correct, confirm. Also does this mean. my string handling operations that operate character by character till they encounter a \0 - will now - with fgets - operate on a newline character as well ?

#include <stdio.h>
#include <conio.h>

int main()
{

    char i[32];

    printf("Enter a string of size 32 or less characters \n");
    gets_s(i, sizeof(i));
    //fgets(i, sizeof(i), stdin);

    printf("With right justification, field width = 32 and precision = 10 -> i = ||%32.10s||\n", i);
    printf("With left justification, field width = 32 and precision = 10 -> i = ||%-32.10s||\n", i);
    printf("With right justification, field width = 10 and precision = 32 -> i = ||%10.32s||\n", i);
    printf("With left justification, field width = 10 and precision = 32 -> i = ||%-10.32s||\n", i);


    _getch();
    return 0;
}

Upvotes: 0

Views: 5557

Answers (1)

chux
chux

Reputation: 153348

How does fgets treat enter key press?

Just like any other key, other than it is 1 of 4 reasons to stop reading more.

" fgets takes the string till an enter key is pressed, " is a causal explanation.

Let us go deeper

char *fgets(char *s, int n, FILE *stream); does not read a string as C defines a string (characters up to and including the null character). fgets() reads a line of characters (characters up to and including the '\n'). It reads them up to a certain point - leaving the rest for later.

  1. A '\n' is read (and saved).
  2. The input buffer is nearly full. (all but 1)
  3. End of file occurs.
  4. Rare input error occurs.

In cases 1, 2 and 3 (if at least something was read), a null character is appended to the input. Now the input is certainly a string and the function return s. In other cases the function returns (char *) NULL.

Note the if fgets() reads null characters, they are treated like any other non-'\n'.

Enter causes '\n': That is a character too.

The '\n' might need to be discarded for later processing. In that case simply lop it off. Since the input might not contain '\n', robust code does not rely on its presence. Nor does robust code assume the first character is not a null character.

size_t len = strlen(s);
if (len > 0 && s[len-1] == '\n') {
  s[--len] = '\0';
}

// OR

s[strcspsn(s, "\n")] = '\0';

OP's explanation of gets_s() has similar detail missing in OP's desciption: special functionality on buffer full, end-of-file and error.

Upvotes: 2

Related Questions