fgets

Get a line from a stream

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Contents

Interface
Description
Return Values
Errors
Security Considerations
See Also
Standards
Page Comments

Interface

#include <stdio.h>char  fgets (char * restrict str, int size, FILE * restrict 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 error. The newline, if any, is retained. If any characters are read and there is no error, 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.

Example:

Example - Get a line from a stream

Workings

#include <stdio.h>
int main()
{
  // open the text file "fred.txt" for writing
  FILE *out = fopen("fred.txt", "wt");
  // write some text to the file
  fprintf(out, "Hello Fred!\n");
  // close the stream, so all changes to the file are saved
  fclose(out);
  // open the file "fred.txt" for reading
  FILE *in = fopen("fred.txt", "rt");
  // read the first line from the file
  char buffer[100];
  fgets(buffer, 20, in);
  // display what we've just read
  printf("first line of \"fred.txt\": %s\n", buffer);
  // close the stream
  fclose(in);
  return 0;
}

Solution

Output:

first line of "fred.txt": Hello Fred!

Return Values

Upon successful completion, fgets and gets return a pointer to the string. If end-of-file occurs before any characters are read, they return NULL and the buffer contents remain unchanged. If an error occurs, they return NULL and the buffer contents are indeterminate. The fgets and gets functions do not distinguish between end-of-file and error, and callers must use reference:ferror to determine which occurred.

Errors

EBADF

The given \c stream is not a readable stream.

The function fgets may also fail and set errno for any of the errors specified for the routines reference:fflush or reference:malloc (3) .

The function gets may also fail and set errno for any of the errors specified for the routine.

Security Considerations

The gets function cannot be used securely. Because of its lack of bounds checking, and the inability for the calling program to reliably determine the length of the next incoming line, the use of this function enables malicious users to arbitrarily change a running program's functionality through a buffer overflow attack. It is strongly suggested that the fgets function be used in all cases. (See the FSA.)

Standards

The functions fgets and gets conform to ISO/IEC 9899:1999 ("ISO C99").

char	`fgets` (char * restrict str, int size, FILE * restrict stream)
char	`gets` (char *str)