getline, getwline, getdelim, getwdelim

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C
Technical Specifications
Dynamic memory extensions
Defined in header <stdio.h>
ssize_t getline ( char ** lineptr, size_t * n, FILE * stream ) ;
(1) (dynamic memory TR)
ssize_t getwline ( wchar_t ** lineptr, size_t * n, FILE * stream ) ;
(2) (dynamic memory TR)
ssize_t getdelim ( char ** restrict lineptr, size_t * restrict n,
int delimiter, FILE * stream ) ;
(3) (dynamic memory TR)
ssize_t getwdelim ( wchar_t ** restrict lineptr, size_t * restrict n,
wint_t delimiter, FILE * stream ) ;
(4) (dynamic memory TR)
1) Behaves like getdelim ( lineptr, n, ' \n ' , stream )
2) Behaves like getwdelim ( lineptr, n, L ' \n ' , stream )
3) Reads from the stream stream as if by fgetc , until delimiter is encountered, storing the characters in the buffer of size *n pointed to by *lineptr , automatically increasing its size as if by realloc to fit the entire input, including the delimiter, and adding a null terminator. *lineptr may be null, in which case *n is ignored and getline allocates a new buffer as if by malloc . The behavior is undefined if delimiter has a value that is outside the range of unsigned char or EOF .
4) Same as (3) , except the characters are read as if by fgetwc and that delimiter must be a valid wchar_t or WEOF .

If *lineptr is not null, the behavior is undefined if *lineptr is not a pointer that can be passed to free or if *n is less than the size of the allocated memory pointed to by *lineptr

As all functions from Dynamic Memory TR, getline is only guaranteed to be available if __STDC_ALLOC_LIB__ is defined by the implementation and if the user defines __STDC_WANT_LIB_EXT2__ to the integer constant 1 before including stdio.h .

Parameters

lineptr - pointer to a pointer to the initial buffer or to a null pointer
n - pointer to the size of the initial buffer
delimiter - the delimiter character
stream - valid input stream, opened by fopen

Return value

The number of characters stored in the buffer, including the delimiter, but excluding the null terminator.

On error, returns - 1 and sets feof or ferror on stream .

Notes

These functions are identical to their POSIX versions except that it is allowed, but not required to set errno on error.

Example

Run this code 
#ifdef __STDC_ALLOC_LIB__
#define __STDC_WANT_LIB_EXT2__ 1
#else
#define _POSIX_C_SOURCE 200809L
#endif
 
#include <stdio.h>
#include <stdlib.h>
void get_y_or_n(void)
{
    char *response = NULL;
    size_t len;
    printf("Continue? [y] n: ");
    if((getline(&response, &len, stdin) < 0) || (len && response[0] == 'n')) {
        free(response);
        exit(0);
    }
    free(response);
    return;
}
int main(void) 
{
    get_y_or_n();
}

Output: 

Continue? [y] n:

See also

gets a character string from a file stream
(function)
(removed in C11) (C11)
reads a character string from stdin
(function)
(C95)
gets a wide string from a file stream
(function)
allocates memory
(function)
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