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getline, getwline, getdelim, getwdelim

From cppreference.com
< c‎ | experimental‎ | dynamic
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.

Contents

[edit] 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

[edit] 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.

[edit] Notes

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

[edit] Example

#define __STDC_WANT_LIB_EXT2__ 1
#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() 
{
    get_y_or_n();
}

Output:

Continue? [y] n:

[edit] See also

gets a character string from a file stream
(function) [edit]
(until C11)(since C11)
reads a character string from stdin
(function) [edit]
(C95)
gets a wide string from a file stream
(function) [edit]
allocates memory
(function) [edit]