FGETS(3) BSD Programmer's Manual FGETS(3)NAME
fgets, gets - get a line from a stream
SYNOPSIS
#include <stdio.h>
char *
fgets(char *str, int size, FILE *stream);
char *
gets(char *str);
DESCRIPTION
The fgets() function reads at most one less than the number of characters
specified by size from the given stream and stores them in the string
str. Reading stops when a newline character is found, at end-of-file, or
on error. The newline, if any, is retained. In any case, a '\0' character
is appended to end the string.
The gets() function is equivalent to fgets() with an infinite size and a
stream of stdin, except that the newline character (if any) is not stored
in the string. It is the caller's responsibility to ensure that the input
line, if any, is sufficiently short to fit in the string.
RETURN VALUES
Upon successful completion, fgets() and gets() return a pointer to the
string. If end-of-file or an error occurs before any characters are read,
they return NULL. The fgets() and gets() functions do not distinguish
between end-of-file and error, and callers must use feof(3) and ferror(3)
to determine which occurred. Whether fgets() can possibly fail with a
size argument of 1 is implementation-dependent. On MirOS, fgets() will
never return NULL when size is 1.
ERRORS
[EBADF] The given stream is not a readable stream.
The function fgets() may also fail and set errno for any of the errors
specified for the routines fflush(3), fstat(2), read(2), or malloc(3).
The function gets() may also fail and set errno for any of the errors
specified for the routine getchar(3).
SEE ALSOfeof(3), ferror(3), fgetln(3)STANDARDS
The functions fgets() and gets() conform to ANSI X3.159-1989 ("ANSI C").
CAVEATS
The following bit of code illustrates a case where the programmer assumes
a string is too long if it does not contain a newline:
char buf[1024], *p;
while (fgets(buf, sizeof(buf), fp) != NULL) {
if ((p = strchr(buf, '\n')) == NULL) {
fprintf(stderr, "input line too long.\n");
exit(1);
}
*p = '\0';
printf("%s\n", buf);
}
While the error would be true if a line > 1023 characters were read, it
would be false in two other cases:
1. If the last line in a file does not contain a newline, the
string returned by fgets() will not contain a newline either.
Thus strchr() will return NULL and the program will terminate,
even if the line was valid.
2. All C string functions, including strchr(), correctly assume
the end of the string is represented by a NUL ('\0') charac-
ter. If the first character of a line returned by fgets() were
null, strchr() would immediately return without considering
the rest of the returned text which may indeed include a new-
line.
Consider using fgetln(3) instead when dealing with untrusted input.
BUGS
Since it is usually impossible to ensure that the next input line is less
than some arbitrary length, and because overflowing the input buffer is
almost invariably a security violation, programs should NEVER use gets().
The gets() function exists purely to conform to ANSI X3.159-1989 ("ANSI
C").
MirOS BSD #10-current June 4, 1993 1
