fgets

Name

fgets, gets
- input of characters and strings

Library

libc.lib

Synopsis

#include <stdio.h>

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

char * gets (char *str);

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 feof and ferror to determine which occurred.

Detailed 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.

Examples

/****************** this program shows reading characters from a file using fgets **************/
/****************** consider input.txt has the following content: ******************************/
/****************** abcdefghijklmn **********************************************************************/
/****************** fdsfdsafsdabcdefghijklmn*************************************************************/
#include <stdio.h>
int main(void)
{
        char buf[20];
        FILE* fp = fopen("c:\\input.txt", "w");
        fprintf(fp, "%s", "abcdefghijklmn");
        fprintf(fp, "%c", "\n");
        fprintf(fp, "%s", "fdsfdsafsdabcdefghijklmn");
        fclose(fp);
                
        fp = fopen("C:\\input.txt","r");
        if(fp == NULL)
                {
                printf("fopen failed\n");
                return -1;
                }
        if(fgets(buf,18,fp) != NULL)
                printf("%s", buf);
        else
                printf("Buffer is empty\n");
        
        buf[0] = '\0';
        if(fgets(buf,2,fp) != NULL)
                printf("%s\n", buf);
        else
                printf("Buffer is empty\n");
        fclose(fp);     
        return 0;
}

Output

abcdefghijklmn
fdsfdsafsdabcdefghijklmn

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, fstat, read, or malloc.

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

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.